Rover 4.6L EFI - to GEM or Thor

[GT8MX]

I am an old noob to this forum.  I'm retired but this is my first post.  

I have decided to install a Rover 4.6L rather than the BOP 215 I have.  I want EFI, so I'm trying to decide between:

1- Rover "GEMS" system
2 - Rover Bosch Motronic "Thor" system

My concern is not power - either yields enough - but hood clearance.  I am stuffing the engine into a Spitfire GT6.  I was worried about clearing the intake+carb+air cleaner stack, but I can't find measurement specs on either GEMS or Thor systems to determine if EFI has better hood clearnace.  I am staying away from the earlier hotwire sysytem in a blind attempt at staying with newer technology in spite of Glen Towery's excellent article "How Glen Towery Installs Rover EFI on MGB V8 Conversions",  The British V8 Newsletter, Volume XV Issue 1.  

Height being equal I would go with GEMS because it is newer and I like the look of the Motronic intake runners rather than the GEMS plenum.  Under the GEMS plenum is a realy neat set of horns, ala Hilborn only shorter,  but they get hidden!

I am intrigued by the EDIS + MegaSquirt  (due to the discussions in thread "Which ECU's will run a 1998 4.6 Range Rover engine?" and talk while fielding a LeMons car  brakingwindracing.com) but I think that is independent of the Induction decision.

I have been reseraching this within the BritishV8 Forum with no luck.  Any info or pointers to info?

Thanks,
Bill
http://spitfiremx8.com/wordpress/

[mgb260]

Another even lower alternative is factory 215 4 barrel intake or Edelbrock Performer intake with injection bosses and 4 barrel throttle body. Could adapt GM,Ford or Megasquirt for ECU.

http://www.mgexp.com/phorum/read.php?40,2495927,2495927#msg-2495927

[Moderator]

I don't know where to get dimensions, but I expect you'll find the Thor system is larger in both height and width. That's a pity, because it looks cool and because its longer runners ought to be advantageous. I considered making a custom plenum to sit atop a Thor lower manifold. At the gasket between upper and lower manifold, the runners have the same round cross-section as earlier Rover systems, as shown here: http://forum.britishv8.org/read.php?11,40102,40373  So... you could use the trumpets from an earlier Rover plenum with the Thor lower manifold. The main reason I went with an earlier manifold and fuel rail is that the Thor fuel rail is of the more modern "returnless" type. (GEMS and earlier Rover systems use a fuel pressure regulator on the fuel rail.) Though I admired the Thor system's handsome stainless fuel rail, adding a regulator to it looked problematic. I also didn't care for the Thor water neck and thermostat installations. I don't know if there's much reason to prefer one injector over another. (GEMS uses Lucas injectors and Thor uses Bosch, right?)

[GT8MX]

I found dimensions for the GEMS EFI from three sources and the heights agree +/- 3/8in.  The sources are http://www.super7thheaven.co.uk/blog/rover-v8-dimensions-a73.html, http://www.locostbuilders.co.uk/photos.php?action=showphoto&photo=v8dimensions.jpg, http://www.v8engines.com/engine-4.htm.

The average height (from the measurements I found) from the lowest point on the stock oil pan to the top of the GEMS plenum is 27-13/16"  The distance from the bottom of the block to the top of the GEMS plenum is then 21-13/16", since the BOP215 stock oil pan I have has a dimension of ~6" from it lowest point to the block mating face.  

That gives me an interference of maybe 3/8" between the top of the plenum and the underside of the hood, but the GT6 hood has a power bulge on the center line, so I might be in good shape with the GEMS induction, provided the power bulge is wide enough to span the GEMS plenum.  At worst, I can mill the bottom plenum like Glen Towery suggest in his article "How Glen Towery Installs Rover EFI on MGB V8 Conversions", The British V8 Newsletter, Volume XV Issue 1 and gain ~7/8".

So I should be OK with the GEMS EFI.

Haven't gotten hard data on the Motronic Thor EFI...

[GT8MX]

Regarding Jim Nichols' earlier post regarding the stock BOP 215 with an EFI throttle body in place of the carb....I would still have an intake + throttle body + air cleaner stack wouldn't I?  The stack is what I am trying to avoid.  Besides, I want EFI.  

[GT8MX]

Regarding Curtis Jacobson's ealier post...

So the GEMS lower manifold is lower than the Thor lower manifold?

What did you want to avoid with the Thor "returnless" fuel supply?  I thought that would be preferrable - one less fuel line, less energy pumping fuel not needed, less chance for a leak - less is more for reliability.

I don't know about the GEMS injectors being Lucas, but I know the Thor injectors are Bosch from the factory.  I suspect any number of maufacturers are now available for non-OEM installations.

[Moderator]

The average height (from the measurements I found) from the lowest point on the stock oil pan to the top of the GEMS plenum is 27-13/16" The distance from the bottom of the block to the top of the GEMS plenum is then 21-13/16", since the BOP215 stock oil pan I have has a dimension of ~6" from it lowest point to the block mating face.

I haven't measured one, but I think you'll find Rover 4.0/4.6 oil pans are significantly deeper than Buick 215 oil pans as shown here: http://forum.britishv8.org/read.php?11,2321

[Moderator]

So the GEMS lower manifold is lower than the Thor lower manifold?

AFAIK 14cux, GEMS, and Thor lower manifolds are all the same height. I'd already decided to make my own plenum. You might possibly want to consider that too... (Snapshots of my results appear here: http://www.britishv8.org/MG/CurtisJacobson.htm)  

What did you want to avoid with the Thor "returnless" fuel supply? I thought that would be preferable - one less fuel line, less energy pumping fuel not needed, less chance for a leak - less is more for reliability.

Maybe, but it's not a free lunch. You still need to regulate fuel pressure AND you need to avoid overheating fuel. This thread might be a good place to start reading on the subject: http://www.msextra.com/forums/viewtopic.php?f=71&t=42907

I suspect any number of manufacturers are now available for non-OEM installations.

Having injectors cleaned and flow tested is a LOT cheaper than buying new injectors.

[mgb260]

On the 4 barrel throttle body there is no stack. Air filter sits on throttle body. As low as you can be. Stock carb intake is lower than fuel injection  manifolds plus no top manifold.  You have to add fuel injector bungs for the injectors.

[Dan Jones]

I think you'll find the long runner Thor manifolds will seriously limit upper RPM performance.  They were designed to increase low RPM power for heavy Range Rovers fitted with automatic tranmissons.  Not the best solution for sports car swap.

Dan Jones

[GT8MX]

Wow.  Great inputs, guys!

So here's the fusion of what I've learned from your inputs:

1 - The lower manifold is the same on GEMS and Thor.
2 - The Thor upper manifold,  while looking cool and generating more low RPM torque, is taller than the GEMS plenum, and limits upper RPM performance (both bad in my application)
3 - I can use my dual-plane factory BOP 4-BBL intake manifold with the low riser throttle body and Megasquirt as Jim Nichols suggest http://www.mgexp.com/phorum/read.php?40,2495927,2495927#msg-2495927.
4 - I can use a GEMS, and fabricate a custom upper manifold to get the clearance I need and incorporate some sort of cold air system ala http://www.britishv8.org/MG/CurtisJacobson.htm

I'm leaning towards #3, but I would fabricate a cold air system because I'm not a fan of the dinner-plate-air-cleaner perched on a throttle body.

But I have a concern...#3 uses a manifold for a carburetor that smooths out the induction pulses through the venturis, but one doesn't have venturis to worry about with EFI.  Instead, with EFI I always see long equal length runners to even out the air flow pulses and maximize the air momentum in the runners.  Plus I often see hotrodders get additional power out of their engines by putting a 1-2" spacer between the carb and the manifold, which would defeat the low profile I'm seeking.

Jim:  

Have you ever seen any dyno runs on the low-pro throttle body +  carb intake manifold (or sims similar to what Dan Jones posted http://forum.britishv8.org/read.php?6,42479 )?

Bill

[Moderator]

1 - The lower manifold is the same on GEMS and Thor.

Similar height, but different in many other ways.

I share your concern about option 3...  

To cloud the issue even more, you could divide "3" into sub-options. There are multiple aftermarket 4-barrel manifolds to consider in lieu of the Buick design. This article shows six of them: http://www.britishv8.org/Articles/IntakeManifolds.htm

[BlownMGB-V8]

You could use short stacks and improve the upper RPM a bit. That would also let you go with a shorter plenum cover if you made your own. Might want to look at the two EFI intakes and see which one has the largest diameter and shortest runners and use that one all else being more or less equal.

Jim

[mgb260]

On alternative #3. You only need a spacer for more top end power. You will gain 20-30 HP on the stock intake by opening the 4 holes into 2 oval openings similar to the Performer intake.  You may have to weld a little if you expose the water jacket under the carb base. You don't want a single plane intake unless you plan on racing. The dual plane stock intake is the lowest profile followed by the Offy, with the Performer the tallest. You should port match any of them. I've seen dyno graphs averaging 30-50 more HP than carbs with same intake.

[GT8MX]

To cloud the issue even more, you could divide "3" into sub-options. There are multiple aftermarket 4-barrel manifolds to consider in lieu of the Buick design. This article shows six of them: [www.britishv8.org]

This article leads me to the dual-plane since I'm not building a race car or track car.  The car will see track time, but it will see a lot more street time.  At least the factory BOP 215 dual-plane intake is one of the lowest.  That's what I am after.

You could use short stacks and improve the upper RPM a bit. That would also let you go with a shorter plenum cover if you made your own. Might want to look at the two EFI intakes and see which one has the largest diameter and shortest runners and use that one all else being more or less equal.

That's what the article by Glen Towery also suggests - lowering the upper manifold - and that may have the least collateral damage.  By lowering the manifold, the plenum is lower, but nothing else has to be changed, except the runners are a little shorter.

I Googled around a bit and found several reviews of the throttle body EFI replacements for a carburetor, and they performed as well as the carb without all the hassles of a carb, but I didn't find a comparison of a long-runner EFI versus the throttle-body EFI, although I remember reading a test several summers ago where HotRod or Popular Hotrodding magazine did just that and got marginally better power from the long-runner EFI..

[BlownMGB-V8]

Am I mistaken in thinking Glen's article deals with cutting down the cover and base plate of the plenum? What I was suggesting might be a little more dramatic. If you removed everything from the short stacks but the bell how long would it be? Less than an inch? The taller ones would be longer of course but this might let you get significantly more than just cutting down the cover and base plate would. In fact I did see one article where the owner cut trumpets into the base plate itself. I have no idea how that worked out, the length of the runners would have been different. But in practical terms the OEM Buick intake is really pretty good. I was running a 7000rpm screamer with one. That and the short 4bbl throttle body and a low profile air cleaner will keep things pretty low.

Jim

[Moderator]

Jim wrote:

Might want to look at the two EFI intakes...

Here they are, side by side:  (with Thor on the left)





I set a couple unmodified trumpets on the manifolds for grins. Thor didn't originally use steel trumpets. 14CUX and GEMS both used trumpets 100mm long.  

Incidentally... I need to clean out my garage. If you want some Rover aluminum to play with, make me an offer.

Bill, you haven't described where you want your torque curve to peak. I'm not sure radically shortening the stacks is a clever idea for a street car. (You could possibly do the Helmholtz resonance calculations to optimize for a specific rpm.) You'll pretty much inevitably end up with shorter overall runner length than stock. My approach was to equalize runner volume, but leave the trumpets as long as I could while doing so.

With regard to modifying four barrel manifolds... if you're going to be milling and TIG welding anyhow, I wonder if you might just as well start with a Buick two barrel manifold? Their advantage is you can pick them up for free (or close to free).

[BlownMGB-V8]

There you go, look at the length of those stacks. Now while it is true that optimal runner volume should be kept close to cylinder displacement, meaning you'd want to thin out those runner walls from the inside at the same time as shortening the stacks if you can (and my wouldn't that be fun), the resonant frequency is dependent on volume and it being desired to move the powerband upwards anyway, trimming the stacks is the practical way to do that, at the same time allowing the cover to be made shorter. The real question is how much, but the calculations should not be difficult. Measure the current volume and then do a proportion based on the OEM torque/HP curve and if you want to go up 20% reduce the volume by 20% by shortening the stacks. Why wouldn't that work?
Jim

[mgb260]

Curtis, That is an excellent idea on the 2 barrel manifold. I think it could be modified very easily with the Edelbrock divided 1/2" spacer. Probably be almost identical for a much lower price. I think Bill already has a stock 4 barrel manifold but, he may want to pickup a cheap 2 barrel one to modify. You can gas weld the intake with aluminum rod similar to brazing. Even use a small Mapp gas bottle. Here is a picture of the fresh air intake instead of conventional air cleaner.

[DiDueColpi]

What about modifying the 4BBl manifold to take the top hat directly.
Then mount your throttle body in front of the top hat.
It would make for a super low profile intake.
Cheers
Fred

[joe_padavano]

"What about modifying the 4BBl manifold to take the top hat directly.
Then mount your throttle body in front of the top hat.
It would make for a super low profile intake."

Or, just buy one of these:

http://www.edelbrock.com/automotive_new/mc/efi/intake_elbows.shtml

[GT8MX]

Am I mistaken in thinking Glen's article deals with cutting down the cover and base plate of the plenum?

You are not mistaken.  That is correct.

Here they are (Thor and GEMS manifolds) , side by side: (with Thor on the left)

Thanks.  If I were to extend air horns toward the front (like a header in reverse) to a plenum box i make, which is in turn, fed air from the front of the radiator, the GEMS lower manifold would look better, I think.

you haven't described where you want your torque curve to peak

I would like it to be in the 3500 area for street use, not race.

you might just as well start with a Buick two barrel manifold

You can gas weld the intake with aluminum rod similar to brazing.

A great idea made easier.  I can't TIG, but I can braze (and epoxy).  I'll look on eBay.

optimal runner volume should be kept close to cylinder displacement,

A good rule of thumb to remember.  Thanks.

Here is a picture of the fresh air intake instead of conventional air cleaner

Yes.  That's what I was picturing for mounting ontop of the throttle body and 4-BBL manifold.

What about modifying the 4BBl manifold to take the top hat directly.
Then mount your throttle body in front of the top hat.

That's a great idea!  That idea is one of those,"why hadn't I thought of that?" Thanks.

[GT8MX]

A follow-on question that perhaps should be a new thread....

In using EFI, am I heading down a path where I will need catalytic converters?  If so, that will be a problem, because it would be hard to find a space to fit them except behind the axle, which might be full of muffler.  I don't believe I need catalytic coverters to pass safety inpsection because the car is a 1968 Spitfire so there are no emission limits that have to be met.

Relevant questions:

1 - Can Megasquirt work with closed loop O2, but no catalytic converters?
2 - Can GEMS work with no catalytic converters?
3 - Can I put the catalytic converters behind the rear axle, with the downstream O2 sensors still mounted behind the converters?  Is that too much of a lag between the O2 sensors upstream of the converters and the O2 sensors downstream which would cause Megasquirt / GEMS to "hunt"?  Or would the upstream O2 sensors need to be mounted behind the rear axle just ahead of the converter?

Thx,

Bill

[GT8MX]

Or, just buy one of these: (Edelbrock intake elbow)

Cool!

[Moderator]

I think you're going to want to become friendly with one of Houston's many welding shops. Nearly every idea floated in this thread involves welding. (Fuel injector bosses!) Some of these joints are going to be very visible too. IMHO, TIG is the way to go.

The welder I used to know in Greensboro was great. I couldn't afford his daytime rates, but he was happy to work on stuff after 9pm while drinking beer and talking about Harley Davidsons with his buddies. His late night rates were affordable.

Megasquirt doesn't know or care about catalytic converters.

A "wanted" ad in our classified section might help you find a sweetheart deal on a 2bbl Buick manifold.