cam option

[Dan Jones]

> basically as much lift as you can get the better your engine will perform
> through the whole rev range regardless of cc's,

That assumes the high lift lobe shape lends itself to the maximum RPM
you are after.  Most cam grinders typically have two primary families
of lobe shapes (along with a host of others for specialized applications
like racing classes with lift limitations or stock lifter requirements,
etc.).  The first family of lobe shapes are optimized for shorter rocker
ratios or lower RPM when used with longer rocker ratios.  These are
sometimes referred to as high torque grinds.  The second family of lobes
are ones designed for higher RPM and/or longer rocker arm ratios (1.7:1
to 1.8+:1).

> the Rover head flows it most cfm when the valve is something like 700
> thou from is seat

Not on any Rover or Buick 215/300 head I've ever had on the flow bench.
Stock Rover heads plateau by 0.5" lift and even my ported Buick 300
heads with 1.775" intake valve peaked at 0.550" lift.  This is largely
a consequence of the valve diameter.  That said, a cam with higher lift
means more time spent near (or above) the heads peak flow.

> lift is related to duration, you cant have lots of lift with little duration
> as the valve will be being opened so quick that the cam follower will just
> dig into the side of the cam profile and break, so with a 600 though lift
> you are going to need 320 deg of duration, what you now have is a full
> circuit race cam that will only make power from 5000 rpm upwards!

That's lobe lift.  Valve lift is lobe lift times the rocker arm ratio
so you can get greater lift from the same cam by increasing rocker arm
ratio.  Unfortunately, the stock Rover ratio is 1.6:1 and no larger
ratios are easily (read affordable) available.  On another engine I'm
currently working on, the stock ratio is 1.73:1 with 1.8:1 optional.
For that engine (351C Ford stroker), I had to go to shorter rocker
arm ratios (1.7:1 intake and 1.6:1 exhaust) to keep lift under 0.620"
(the limit the BBC beehive valve springs can tolerate), even with a
street cam (hydraulic roller).

For flat tappet cams, the maximum lobe lift slope is determined by the
diameter of the lifter.  Unfortunately, the Rover diameter is 0.842"
(same as other GM V8's such as the small block and big block Chevys,
Pontiac and Buick V8's).  Small and big block Ford V8's use a larger
0.875" diameter and Chrysler and AMC V8's use an even larger diameter
of 0.904".  One way around the lifter diameter limitation is to use
mushroom tappets which have a face that is larger than the lifter
diameter.  The downside is the lifters have to go in from the bottom
side of the block, before the crankshaft goes in.

> Duration is the time the valve is lifted of its seat, to little you will have
> no power too much the car will drive like a pig, However duration, LCA "lobe
> center angle, and overlap are all related, its not so much the duration that
> kills drivability its the overlap, just 10 deg can make or break the engine!

Overlap is much more important than duration.  Overlap is the period when
both intake and exhaust valve are open.

> The LCA is the angle between full lift on the inlet and full lift on the
> exhaust lobe, by making this wider you can tame the cam for the same given
> duration

Because you've decreased the overlap.  Overlap is the combination of duration
and LCA.  The best approach is to pick the total overlap to set your desired
RPM range, choose the optimal LCA for your particular engine and then duration
will fall out of the equation.

> however what will happen is the cam with the wider LCA will idle
> better drive smoother make more bhp and have a wider torque curve,

A wider LCA does not necessarily make better peak or average HP.

> the cam with the smaller LCA will only have a benefit in the mid range,
> around peak torque.

In many engines, particularly Rover storker engines, tighter lobe centers
will make better power across the rev range.

> so in my honest opinion for a road cam I like to go for around 285-290 deg
> of duration with a wide LCA around 114, this to make a good road sports cam,
> you can drive it down the shops with no hunting and use it on a track day
> as well,
>
> the same cam on a 108 LCA will make it more peaky in the mid range, but
> you will have to keep changing gears in slow traffic and it will drop off
> the cam quicker too, peak power will be around the same but where the 114
> will still be making good power at say 6500 rpm the 108 will be dead and
> buried and need a gear change,

That's not a apples-to-apples comparison.  For a valid comparison, you
need to have equivalent overlap.  In the above example, the 108 LCA cam
has far great overlap so tunes in at a higher RPM.  If 108 is the optimal
lobe center, then reducing the duration so the overlap is equivalent will
yield a cam that makes much better average power under the curve than the
114 LCA cam.

In "Be the Camshaft Expert" (July 2006 issue of Popular Hot Rodding),
David Vizard presented some rules of thumb for selecting cam specs based
upon what he's learned in developing a cam selection program.  An online
version of that article can be found here:

 http://www.popularhotrodding.com/tech/0607phr_camshaft_basics/index.html

The program was reportedly 18 years in the making and uses data gathered
from several thousand cam tests.  The basic idea is that cam overlap sets
the RPM range in which an engine will best operate and the total overlap
is a function of the cam duration and lobe center angle (LCA).  If you
know the ideal LCA and the RPM range you wish to operate in, the duration
will fall out.  In the article, Vizard presents graphs of cubic inch
displacement (CID) per cylinder per inch of valve diameter versus ideal LCA.
The graphs are for inline valve heads with compression ratios between 9:1
and 11:1.  If canted valve heads are used, the ideal LCA is 2 degrees less.
The optimal LCA is also adjusted for compression ratios outside the assumed
range.  Once ideal LCA is known, you pick your desired overlap via
application:

 1. Street towing       10 to 40 degrees
 2. Regular street      30 to 60 degrees
 3. Street Performance  50 to 75 degrees
 4. Street/Strip        70 to 90 degrees
 5. Amateur Race        85 to 100 degrees
 6. Professional Race   95 to 115 degrees

Overlap is the period when both intake and exhaust valves are open and serves
to set the RPM range over which the cam will be best suited.  More overlap
means a rougher idle and poorer low end response due to reversion of the
exhaust charge into the intake plenum as well as loss of "effective"
compression ratio (compression is literally blown out the exhaust port at
low RPM).  Where you fall in the overlap range is a function of valve size
per cubic inch.  Big valves on a 302 use the low end, a 350 with typical size
valves use the mid-point, big inch small block or big block, use the right
hand side.  Given the small valve size of the Rover/Buick aluminum V8's,
we'd typically use the larger overlap value (right hand side).  Once LCA and
overlap are known, duration falls out of the equation.  Lift is determined
by the intake valve diameter.

In the article, Vizard presented the results of a test demonstrating the
importance of picking the right LCA:

 http://www.popularhotrodding.com/tech/0607phr_camshaft_basics/photo_09.html
 http://www.bacomatic.org/gallery2/v/hidden/dan/dan-cars/album10/album15/LCA_comparison.jpg.html

Ideal LCA for that engine was 108 degrees.  Narrowing to 105 degrees made
similar power but had noticeably worse idle and low speed characteristics.
Widening to 111 degrees lost power.  Another LCA test was performed on a
302 Small-Block Ford and repeated on a stroked (347 CID) version of the same
engine:

 http://www.popularhotrodding.com/tech/0607phr_camshaft_basics/photo_12.html

 "When used in the 302, the 276/280 roller hydraulic cam on a 110 LCA proved
 optimal, as even a 1 degree change either way produced worse results. Using
 a SCAT stroker kit, this engine was stretched to 347 inches and re-tested
 with the original 110 LCA cam. The stroker kit really helped both power and
 torque. When the 110 LCA was replaced with a more appropriate 108 LCA cam,
 the output made a further jump to the tune of some 20 lb-ft and 20 hp.  The
 108 cam in the 347 gave as much in terms of idle and vacuum as did the 110
 LCA in the 302. Dozens of tests such as this show conclusively that the
 overlap and LCA--not the duration--are the first steps toward generating a
 cam spec."

At low speed, lots of overlap is bad as it hurts low end but overlap helps
as the RPM increases.  To a degree, you can offset overlap with static
compression.  Another point raised in the article is that, for most V8's with
reasonable heads, the ability to raise low speed torque with compression
increase holds to around 285 to 290 degrees (at lash point) of cam duration.
After that, drop off is faster than an increase in compression can recover.
In another article ("Compression Comprehension") about running up to 12:1
compression on pump gas, Vizard presented the results of a compression test:

 http://www.bacomatic.org/gallery2/v/hidden/dan/dan-cars/album10/album15/CR_vs_low_speed_output.jpg.html

"When used in conjunction with a bigger cam, increased compression can
 work wonders for the entire curve. When a 265-degree cam (gray curve)
 was substituted for a 285-degree cam (blue curve), a substantial drop
 in low-speed output was seen. Raising the CR from 9:1 to 12:1 recovered
 almost all the lost low end and gave a further increase in top-end
 output"

I wrote a little computer program based upon the article.  The required
inputs for the simplified program are:

 bore diameter (in inches)
 crankshaft stroke (in inches)
 intake valve diameter (in inches)
 static compression ratio
 canted or inline valve heads
 desired overlap (picked from the ranges listed above)

Some results for various Rover/Buick combos are presented below.  Vizard's
cam selection program is not available to the general public but I know for
a fact it takes much more into consideration than the simplified rules
presented above.  A friend has run his program and it uses actual head flow
data, port size (length and cross-sectional areas), valve diameters, rocker
ratios, desired idle vacuum, compression, bore, stroke, fuel octane,
thermostat temperature, rod length and more.  Basically, it attempts to feed
the "air pump" in the most efficient manner, given the parameters entered.
What it doesn't do is tell you what ramp rates you need.  The recommendation
is to use the most aggressive ramp you can tolerate for your application.
However, more aggressive lobe shapes are noisier, wear more quickly and are
harder on valvetrain parts so that needs to be taken into consideration as
well.

The simplified program assumes you'll use the same lobe profile for intake
and exhaust.  There's an implicit assumption that the exhaust flow is
reasonable compared to the intake.  Vizard also suggests the rocker ratio
on exhaust is best kept 0.1 to 0.2 of a ratio lower than the intake ratio.
The exhaust is under higher pressure and blows down early in the lift cycle
plus the exhaust is less sensitive to valve acceleration than the intake but
is sensitive to duration.  I noticed in last year's Engine Masters Competition,
most of the entries were using shorter rocker ratios.  If an existing cam's
LCA is too wide, higher ratio rockers may increase output.  For rocker ratios
between 1.5 to 1.9, each 0.1 ratio increase on the intake, the LCA needs to
be spread by 0.75 to 1.  Be aware there are cases where the ideal lobe center
may be too narrow for acceptable street manners.  For instance, when stroking
an engine (keeping all other variables constant), Vizard suggests tightening
the LCA up by a degree for something like every 16 cubic inches increase in
displacement.  That will lead to very tight lobe centers which may not be
acceptable for certain applications.  For instance, an engine equipped with
mass-air EFI (which will measure reversion flow as if it were induction flow)
might not be too happy with 104 degree lobe centers.   Vizard's full-up
program allows you to specify idle vacuum to get around problems like that
but the simplified program doesn't have that sort of flexibility.

Another thing to be aware of is that narrow lobe separation angles require
an efficient exhaust with minimal back-pressure.  If you have a bunch of
back-pressure (from things like restrictive mufflers or headers that turn
down sharply at the exhaust port exit) it will hurt a narrow lobe separation
angle engine more than a wide one.  A quote from the article drives home this
point home:

 "Let's make one thing clear here: Big (but not excessive) overlap is a prime
  key to big power numbers, but only if your exhaust system sucks. Literally.
  If you have ever heard that an engine needs a little backpressure, you might
  want to ask yourself why an engine would want an exhaust system that literally
  pushes exhaust back into the combustion chamber rather than sucking it out.
  The simple answer is, it doesn't. If a big-overlap, big-cam engine has an
  exhaust system with any measurable backpressure, the price paid is a big drop
  in output."

If your exhaust system is restrictive, it may be wise to err on the side of
a wider LCA or shorter duration.

Since large valve heads tend to increase flow through high lift levels,
the lift recommended by Vizard's rules may be excessive for heads equipped
with large valves.  The recommendation is to use a lift consistent with your
reliability goal (higher lift wears valves, guides and seats more quickly).
However, for small valve heads, like our little Rover/Buick aluminum V8's,
the maximum lift is reasonable.  In the range of 2 valve pushrod V8's, our
Rovers are at the small valve diameter (per displacement) end of the spectrum
but, based upon my limited experience, the simplified program seems to give
pretty reasonable trends.  As a starting point, you could do worse.  Woody
Cooper has had a lot of experience with custom cams in Rovers of various
displacements and I believe his experience parallels Vizard's predictions.

Cam specs for Rover/Buick street performance assuming 75 degrees overlap
and 9:1 to 11:1 compression ratio:

 CID Bore x Stroke Intake   duration / LCA / Lift
                   Valve
                   Diameter
                   
 215 (3.50 x 2.  1.5      298 / 112 / 0.45 to 0.52
 219 (3.52 x 2.  1.5      298 / 111 / 0.45 to 0.52
 215 (3.50 x 2.  1.625    298 / 112 / 0.48 to 0.56
 266 (3.53 x 3.4)  1.5      288 / 107 / 0.45 to 0.52
 266 (3.53 x 3.4)  1.625    292 / 109 / 0.48 to 0.56
 292 (3.70 x 3.4)  1.625    288 / 107 / 0.48 to 0.56
 292 (3.70 x 3.4)  1.775    292 / 109 / 0.53 to 0.62
 297 (3.73 x 3.4)  1.775    292 / 108 / 0.53 to 0.62

Note that the durations used here are seat-to-seat duration (similar to
advertised or SAE duration, not duration at 0.050").

Okay, so that's the theory. Here's some of the practice side from an
engine builder friend of mine...

If you set up a cam on blocks or centers and use a lifter jig, or plot
it out on paper, it quickly becomes apparent that the range of actual
lobe profiles is sharply limited. For flat tappet cams, the diameter of
the lifter or the length and curvature of the finger follower defines
the limits of possible profiles. Once your pressure line gets to the
edge of the follower, there's no more to be had. For rollers, the
diameter of the roller is your limiting factor. Eventually the pressure
line reaches the height of the axle, and spits the roller off to the side.

That's geometry. It does make a difference; that's why flat tappet
racing lobes are specified by lifter diameter, and why rollers go to
inverted flanks.

Then you need ramps to take up the slack on opening, and to keep from
pounding things on closing. That further restricts allowable profiles.

Then you come to the big real-world part - wear. For a flat tappet,
wear is pretty much a function of load at the pressure line. That's why
Detroit cams are all so wimpy. They had to last 75,000 or more miles
without wearing to the point where they had to be replaced. For
hydraulic rollers, oil viscosity and pressure are your main limits,
where leakdown starts to change the valve motion significantly from the
lobe motion. And remember, that's assuming a 10 year old car that still
has the oil it left the factory with, in a worst-case service condition,
like pulling a camping trailer in New Mexico in the summer.

For a "performance" cam, longevity is sacrificed first. You can load
the cam more heavily, and shorten the ramps, and pick up lots of "free"
power by kicking the valves open faster and closing them sooner.
Competition Cams is infamous for this; some of their more aggressive
street cams seldom saw more than 20,000 miles before rounding off lobes
or hollowing lifter bases. They *did* perform as advertised. Note
that Comp recommends armor-faced lifters for flat tappet lobes that
require heavy spring rates.

For "street" cams, you have to assume the stock valve springs are being
used, because a largish fraction of your customers *will* insist on
running them. Getting more area under the curve with stock springs is
a damned good trick; you can whack it off the seat, but you have to stop
lifting early and carefully to keep the valvetrain together at max lift,
and you have to set the valve down carefully to keep it from bouncing.

Drag cams are quite specialized now, which is why you see the lobes
separated from circle track stuff. Longevity on a cutting-edge drag cam
is often less than a dozen runs for a flat tappet. For solid rollers,
lifter failure happens first.

Power is cheap. Longevity is what costs the big money.

Crane and Isky like to talk about stepped lobes to handle harmonic
motion of the valvetrain bits, and other crap like that. It's just
marketing; on the dial indicator, it's all a smooth curve.

What's creepy is to mike a brand new cam, and find .005" difference in
lobe height from smallest to largest. Kind of makes me laugh at Crane,
which claims accuracy down to *millionths* when tossing cams into the
grinder...

Extended exhaust duration only adds overlap, with its attendant idle
and emissions problems. All-out racers use long exhaust durations for
scavenging, but that ruins your fuel economy on the street. It's primarily
a drag race trick to keep the power from dropping off quickly after power
peak. On the street, a symmetrical profile or even a short exhaust will
run just as well and with a lot more tractability. On the street, extended
exhaust profiles date back to the 15-psi-backpressure old-style catalytic
convertor days; they are obsolete.

Overlap creates a lot of internal EGR during cruise which is great for fuel
economy if the spark is advanced enough. In the BMW world, intake and
exhaust cam profiles are either the same, or the intake gets the bigger cam.
Independent runner intake manifold can withstand a lot more overlap without
trashing the low speed torque and tractability than a standard plenum carb
intake.

Dan Jones

[Moderator]

One of these days I'm gonna succeed in convincing Dan to write articles for BritishV8 instead of (or in-addition-to) putting so much effort and information into message-board posts. They'd be such a valuable reference and they'd probably reach so many more people. (Tables and charts would also be easier to integrate.)

Awesome and thought provoking information!

A bit overwhelming though, for non-motorheads like me...

[NixVegaGT]

An interesting feature I wanted to also mention is the lobe lift at .34 is just about as big as it looked like you could make it without making the camshaft weak. As it is, the back side of the lobe is almost even with the main shaft of the cam and in some places looks like it is at the diameter of the main shaft.

I'm starting to reconsider running E85 again. Do you think there is any difference in cams for that? Probably not but interesting to thing about. I think after I CC the heads and get a clear understanding of my actual CR I'll decide. I figure if I'm under 11:1 gasoline. If I'm over that I might consider E85 again. I initially threw out the idea because of the expense in converting a carb for it but the are getting less expensive now.

Just tossing in wrenches. LOL!

[BlownMGB-V8]

Good stuff Dan. It's really great to have someone around who ponders and really understands these things. But what happens when you add boost? I mean just from reading your post and having not yet followed the links...(I will, count on that) it would almost sound like I'd be better off to just stick with a stock cam. Here I am thinking that it'd be an advantage to help the exhaust side since the intake is getting a boost (literally) and you up and say extended duration on the exhaust ain't all that great shakes.

But I'm looking for the practical solution. Something to let me take advantage of the Scat rods, Venolia pistons, CC springs and Eaton blower but keep the economy and driveability of the 10 to 11:1 CR. But I don't want to make a study of it, just want to find a decent bump stick.

340 Buick, stock '64 300 heads.

Jim

[NixVegaGT]

Jim I would try calling Woody: 1-508-880-5448 OR email him:  Woody@TheWedgeshop.com

He's got a lot of practical cam experience since the late sixties. He might have a good thought or two on it or he may know a good resource.

Whatever your findings, post'em. I'd be really interested in knowing. Not for my project but I just love to know why things work the way they do.

Thanks for staying in the thread.

[Dan Jones]

> One of these days I'm gonna succeed in convincing Dan to
> write articles for BritishV8 instead of (or in-addition-to)
> putting so much effort and information into message-board
> posts. They'd be such a valuable reference and they'd
> probably reach so many more people. (Tables and charts
> would also be easier to integrate.)

One of these days I'll get around to finishing one of those
articles but things are very busy at the moment.  Outfitting
the new shop and running the dyno program are taking up
most of my free time.

Dan Jones

[BlownMGB-V8]

I emailed Woody and he is going to see what he can come up with. He feels the challenge might be to get 7 grand out of the stock alloy 300 heads.

Incidentally Nick, have you checked your rod to cam clearance? I'm out of space. I'll have to grind the shoulders of the rods to keep from hitting the cam lobes, they just graze with the stock cam. I think that's going to limit my lift to very near stock. I don't think Woody will be happy. Wonder how much clearance you need? I'd think about .020" would do it.

Jim

[NixVegaGT]

Interesting! I am about to start assembling the bottom end. I will be careful and post what I find. I figure I'm about three weeks away from that.

Thanks Jim!

[BlownMGB-V8]

Glad to help.
I wish I had some input on what is considered adequate clearance between the cam and the rods. I'm thinking .020-.030" would do it.

I could get that by reducing the base circle of my cam and get a more performance oriented grind in the process. Currently I have a 1.175" base circle, 1.020" minor diameter and 1,425" lobe for .250" lift (.400 at the valve) so if I reduced the lobe height by .030" to get clearance and then reduced the base circle to get lift back it would seem I could go as high as .490" at the valves and possibly even get a little more duration. Does this make sense?

Jim

[MGBV8]

The Chevy stroker guys say .050". The BIG stroke engines go with .080" due to crankshaft flex. I would use the smaller base circle cam as a last resort.

[BlownMGB-V8]

Thanks Carl, that really helps. I do think we're looking at last resorts here, the only other option is to mill down the shoulders of the rods and with them already finely balanced I just hate to do that, plus there isn't a whole lot to be gained there before getting into the threads. I may end up doing both though.

Disadvantages of a reduced base circle? Can't really be a strength thing since the weak points are the minor diameter and I wouldn't be changing that. It used to be pretty common practice to regrind cams. Even at .050" clearance I think there's still room for .500" lift and I don't expect to need more than that.

Jim

[Dan Jones]

> Here I am thinking that it'd be an advantage to help the exhaust side
> since the intake is getting a boost (literally) and you up and say
> extended duration on the exhaust ain't all that great shakes.

Vizard's cam rules apply to normally aspirated engines.
Different rules apply to supercharged engines.

> But I'm looking for the practical solution. Something to let me take
> advantage of the Scat rods, Venolia pistons, CC springs and Eaton
> blower but keep the economy and driveability of the 10 to 11:1 CR.

You've got some mis-matched parts there that make specifying a cam
difficult.  You're trying to vent a 340 cubic inch engine plus
boost through a 1.3" exhaust valve.  You're limiting lobe lift
bacause of a rod clearance issue and your trying to run boost on
top of high compression on pump gas.  

> Disadvantages of a reduced base circle?

Might be worth a call to Erson (Steve Tanzi) if Woody doesn't have
a call in for you already.  If the cam core has been heat-treated
already, there is a limit to how far you can grind before breaking
through the heat treat.

Dan Jones

[BlownMGB-V8]

I take it you disapprove. I don't mind that, but perhaps it would help a bit if you better understood where I'm coming from. To start with I really don't need more power than I have right now with the 215. I have other goals in mind. But since it *is* a 350 (340 + .050") I might as well bump it up a little. Did I state the power goal? 400hp is not a lot to ask from a 350, even normally aspirated. Why do I want it to turn 7 grand? Because I *like* it. Not because I expect a big power boost above 5000. Why am I putting a blower on it? To overcome the restriction of those small valves you mentioned. Why am I using such small valves? Two reasons, money and money. Gas and machine work. The high compression is also for the first of those two reasons, plus low end torque. The intercooler is for the low octane fuel. (Who said I was going to run regular in it? That would be a switch.) Also, I want a cast iron block, and I want to put a Buick 340 in my MGB.

This car may very well never see another drag strip, but it *will* be taking on the back roads of KY and West By God Virginny. For that I don't need as much power as I have now. Heck even without the blower this engine might blow the doors off the 215.

I do appreciate your comments. I would appreciate them even more if they were more to the point. I know quite well this is a challenging application. Convention has been thrown out the window. I'm on a quest here to get what *I* want and that's a long ways from the mainstream.

Jim

[hoffbug]

FYI..
 Harold Brookshire  former owner of Ultradyne and designer  for Reed, Lunati, and others offered up this cam info.


I have a very reliable solid lifter cam of the following specs:

.020 282/292
.050 248/255
.200 155/162
valve lift, 1.6s
.536"/.551"
LCA as wanted...

This would be a healthy cam in an engine of that size...
It has gone over 100,000 miles in street SBCs, and needs the valves adjusted at least once a year.....
I also have much more aggressive solid lifter cam lobes.
The lowest lifts I have with rollers are about .550" with 1.5s.

Cores for the Buick 215/300/340 are available, but from a supplier.
 It will take 5 to 7 working days to have in the shop.
Mike, who was my shop foreman at UltraDyne for 19 years, and who now is shop foreman and Landis operator at Lunati, reminded me that the cores do not have a lot of meat on them, and the cam will need to be ground straight-up, with no advance.
Costs? Around $220 right now.
If I can help, please let me know......

Harold Brookshire

662-562-4933

[BlownMGB-V8]

Interesting. I don't really want to run a solid lifter cam because I have no provision for lash adjustment. Lift will have to be limited to .500 on a 1.020" base circle to leave .050" rod clearance. The cam used for inspection has a 109* LCA and .250" lift at the lobe. (.400 at the valve).

I would like to keep the intake lobe reasonably mild for good driveability and economy and run an agressive exhaust lobe to allow better evacuation of the cylinder under boost.

Jim

[madmax]

QUESTION:  (esp to Nick)

What have you done to the Heads to improve flow?

The airflow of rover heads needs to be improved before ANY high lift cam makes a difference.   This is why the "stock" cam works so well... it's matched to the head ports.   Bolting a higher lift, longer duration cam into "stock" heads has been shown on the dyno to make little, if any, difference!

I'd make sure the heads can flow for those larger valves.  You'd want something better than 160 cfm (intake) and 130 cfm (exh) for those size valves at that lift. (Those are 28" merc. readings.)  

Just bolting a lot of "bigger" parts on isn't going to make any difference if you haven't changed the flow characteristics of those heads.   They have always been the limiting factor to performance of that motor....

$.02

[Dan Jones]

> What have you done to the Heads to improve flow?
> I'd make sure the heads can flow for those larger valves. You'd want
> something better than 160 cfm (intake) and 130 cfm (exh) for those
> size valves at that lift. (Those are 28" merc. readings.)

Switched to 1964 Buick 300 heads, ported with larger seats and valves.
CFM is just under 200 on the intake and a little over 150 on the exhaust.

> The airflow of rover heads needs to be improved before ANY high lift cam
> makes a difference.  Bolting a higher lift, longer duration cam into
> "stock" heads has been shown on the dyno to make little, if any, difference!

Some dyno results below which do show HP increases.  As with any
engine it's the incremental contributions of the combination that
make power.

> This is why the "stock" cam works so well... it's matched to the head
> ports.

I never found the stock cam to be particularly good.  HP is directly
proportional to RPM.  Cam duration drives RPM.  The stock cam has too
little duration to support much in the way of RPM.

> Just bolting a lot of "bigger" parts on isn't going to make any
> difference if you haven't changed the flow characteristics of those
> heads. They have always been the limiting factor to performance of
> that motor....

Way back in 1961, Hot Rod Magazine presented the results of dyno
testing on both the Olds and Buick 215's.  Starting with a 2 barrel
Buick that dyno'd at 136 HP, they ended up with a high compression
2 x 2 bbl engine that made 233 HP.  Changing from the stock cam to
an Isky E2 cam, it went from 177 to 215 HP (Hedman headers and larger
carbs were installed at the same time).  In the testing sequence
of the Olds, they went from a stock cam to an Isky E-4 and went from
172 to 194 HP.  Head porting on the Buick picked up 7 HP.

More recently, Ted at T.S. Imports provided the results of a dyno test
on a Rover 3.5L and the results were published in a 1995 British Car
article "Improving the TR8 & Buying a TR8", Dave Destler, 1995 British
Car, pp 35, 47-48.  The "V8 on the Dyno" sidebar gives the relevent
information:
 
  conducted by Ted Schumaker of TS Imported
  rebuilt 3.5L Rover V8
  stock bore and stroke
  unmodified cylinder heads
  22 lbs steel flywheel (stock is 32)
  Tri-Y TR8 headers
  10.5:1 compresson cast aluminum pistons
  Isky 264 hydraulic flat tappet camshaft

  Run 1:
  Holley 390 carb, vacuum secondaries, #51 primaries, #58 secondaries, Offy
  JWR dual port manifold, 22 degrees advance, vacuum advance disconnected

   RPM   Torque  HP
   4000   211    161
   4500   210    180
   5000   205    195
   5500   189    198
   5700   189    205
   5900   181    204
  Run 2:
  Holley double pumper 390 carb, mechanical secondaries, #62 secondary jets,
  Offy/JWR dual port manifold, 28 degrees advance, vacuum advance disconnected

   RPM   Torque  HP
   4000   ---    ---
   4500   219    187
   5000   210    200
   5500   197    206
   5700   191    207
   5900   182    204

A later test was run with an Edelbrock Performer Rover intake and and the
results published in the MGB V-8 Newsletter, Issue III, Vol. I:

  Run 3:
  Edelbrock Performer Rover dual plane manifold, 30 degrees advance

   RPM   Torque  HP
   4000   232    177
   4500   230    197
   5000   222    212
   5500   215    226
   5700   217    235
   5900   207    232

Dan Jones

[Dan Jones]

> Head porting on the Buick picked up 7 HP.

I was surprised the head porting didn't pick up more.
I suspect the dual plane intake manifold was at fault.
If the intake manifold is more restictive than the
cylinder, which is usually the case with dual plane
intake manifolds, then you won't realize the cylinder
head's potential.

Dan Jones

[NixVegaGT]

Thanks for picking up the ball on this one, Dan. The answer is yes 300 heads larger valves and porting. Right now I have my heads back in the shop again to have beehive springs from CompCams installed. I'm also considering taking the heads to the next level from a port standpoint. My engine machine shop has a porter with a good machine but it couldn't hurt to toss in a couple pointers on specifics for the porting.

Do you have diagrams for where the most flow yield is to be had from the 300 heads, Dan? Where should I tell my guy to focus?

BTW here's a link to my head mod page:

http://www.cardomain.com/ride/2357894/2

[BlownMGB-V8]

I think the 300 heads have 52 cc chambers as well so a different piston might be needed. Olds 4 bbl and Jetfire heads should be the same as the Buick and Rover, while I think the 300's are close to the same as the 2bbl Olds.

Nick, are those behives going on 300 heads? Since you are using them, could you ask if they will fit the Olds heads also? Lighter retainers should be a plus.

Jim

[NixVegaGT]

OH one more thing. I'm planning on going with the Harcourt single plane. It's got a pretty big plenum. The middle ports are going to have the best access to the carb. I'm also concerned about the fuel ratio imbalance between 7 and 2 because of the firing order. because 5-7 fire in order, fluid dynamic inertia will favor 7 and that has to reverse to get to 2.

What do you think? Do I need to insert dams at 7 or something? Or just let it go? I did find a dyno place that will tune on the engine dyno with wideband at each cylinder...

[NixVegaGT]

I'm not sure what the difference is in the pocket size for the Olds head. I've only worked on the 300 head. From what I understand the springs I used for that setup with a mildly aggressive cam were for a SBC. What is the Pocket dia for the Olds?

The Buick pocket dia. will take 1.260" dia. springs. I'm ordering CompCams #: 26915 for the LS1. It's seat pressure is 105 lbs. and 290ish lbs. open. It's dia. is 1.290" but I'm pretty sure I can have 30 thou machined open. The spring height is 1.7 for my cam choice.

The comparable standard spring would be TA_1436 from TA performance. Here's a link with details.

http://www.taperformance.com/products.asp?cat=408

Sorry I couldn't find any reference to the spring dia for the Olds. Post it if you can, Jim.

[Dan Jones]

> Do you have diagrams for where the most flow yield is to be had from the 300 heads,
> Dan? Where should I tell my guy to focus?

No diagrams but take a look at the close-ups here:

 http://www.bacomatic.org/gallery2/v/hidden/dan/dan-cars/album10/album12/Buick_300_ported_chamber_closeup.jpg.html
 http://www.bacomatic.org/gallery2/v/hidden/dan/dan-cars/album10/album12/Buick_300_ported_intake_port_closeup.jpg.html
 http://www.bacomatic.org/gallery2/v/hidden/dan/dan-cars/album10/album12/Buick_300_ported_exhaust_port_closeup.jpg.html

I'm not sure if you have the option to view the full resolution like I do but try this link:

 http://www.bacomatic.org/gallery2/v/hidden/dan/dan-cars/album10/album12/Buick_300_ported_chamber_closeup.jpg.html?g2_imageViewsIndex=1

If he's ported Buick V6 heads before, the Buick 300 responds to similar work.  The bowl area and short side
radius are the areas to pay the most attention.  I'll compare a stock Buick 300 head to my ported heads
this weekend to see if I can come up with anything more specific.

Dan Jones

[NixVegaGT]

Thanks Dan. I'll pass these on to my porting guy. I'll also mention the info about the Buick v6 heads.

[BlownMGB-V8]

Nick I'm sorry to say I can't answer that question. Heads from the blower motor left today and the only other Olds heads I have have been converted to straight springs. I do know the Buick 215 and 300 can use the same springs and suspect the base of the Olds spring is the same, but I have no way of knowing for sure.

Jim