BritishV8 Forum

The engine is "adequate" with the 3.4" stroke, even with the 2bbl intake. The 3.85" stroke makes it better. Good heads make it better. Light pistons and rods make it better. A roller cam makes it better.  A blower makes it better. TBI and mappable dizzy make it better. It's mostly a question of budget and how carefully you can spend it.

I sort of understand you de-stroker guys a little bit, but it's really going too far in the other direction. A stroker 300 with light rods, pistons, wrist pins, and aluminum flywheel will rev faster than is really comfortable on the street and a 7K redline is as easily achieved as with the short stroke. So what are you gaining? Because it isn't economy.

Here's the thing. You say you want a fast revving engine but it still has to move the car. With any given load and at any given engine speed assuming gear ratios and tire sizes are the same the engine with more power will accelerate the car faster. At any given rpm and assuming equal builds the engine with more displacement will produce more power. So the bigger engine will rev faster. Until you get significantly over 7000 rpm you really aren't going to change that and the 3.850" stroke SBB is quite capable of redlining at 7 grand if it's built right. De-strokers have their place but it is usually in racing where rules restrictions artificially influence natural progression such as F1. On the street things are a bit different. And yes, we all loved the SBC 302, but that was a very special engine built specifically for racing. Again, Rules.

Jim

Back to the heads, big difference between the two 300 heads, too much really for just using a different flow bench it seems. Something there doesn't quite add up.

Jim

Art, I hear what you're saying.  But as Jim says, it's a question of budget.  I think, to a certain extent, those TA heads are probably not necessary (and money that I can use elsewhere--such as having EFI, which will make the car way more drivable).  Without them, I still think I can get to the high 300s in horsepower, which along with the torque curve that engine should have, should make it fun, but not scary.  On the other hand, we haven't been discussing gearing either.  I wonder how much can be gained in having a balanced driving experience by having the right gear ratios.  I am thinking that my rear axle ratio might be around 3.55, to keep me from burning up a set of tires too fast.

Went back and did some more on piston options for the 300 heads.  This one looks very promising.

Eric, What piston is this? What pin size?

Jim,

It's a Chevy forged racing piston:  https://www.summitracing.com/parts/dms-1-2803-3780  It has .927 pins, so a bit of honing/reaming and rebushing will be required on my rods, but from what I can tell, it should still leave plenty of material at the small end.  And while they are more expensive than many of the pistons I've been looking at, at $537 they are not unreasonable.

"At any given rpm and assuming equal builds the engine with more displacement will produce more power. So the bigger engine will rev faster."

I don't follow that logic.


" I am thinking that my rear axle ratio might be around 3.55, to keep me from burning up a set of tires too fast."

I think the engine on your drawing board is going to eat up the tires even with that 3:55 gear, Eric.  May want to look into a 3:08.  

Good advice Carl.  I was wondering about that.  I actually might be in luck--I think it's possible that my rear end has a 3:08 gear.  Haven't looked at it in quite awhile, I need to dig it out.

3.08 vs recapture rates.  In other words, pavement velocity vs tire velocity. If you break loose 3.08's in a smoking way, that much harder to recover versus higher numerical ratios.

'Cept 3.55, 3,9, 4.11, etc are easier to smoke.  

Sort of depends on your transmission ratios, particularly 1st and OD.

I think my OD ratio is around .8 and with a 3.54 axle ratio I found I wanted a tall tire. I'm currently running a 26.5" diameter and it's just within the edge of the comfort range but off the line performance is exceptional. I think my 1st gear ratio is probably the 2.95 one or close. Running the larger tires is the equivalent of having a 3.18 axle ratio. If running the .67 OD things would be different and if 1st was over 3.0 with these gears that wouldn't be much fun. A 3.08 could work with the 2.95 1st of course, giving just over 9:1 in 1st but the .67 with the 3.08 gives a 2.06 final ratio and means a big jump from 4th to 5th. I think the 3.08 is a good ratio, just at the opposite edge of the comfort range. Based on the performance of the Roadmaster with it's 2.88 and .67 OD I'd say that's fairly accurate. With a smaller engine you'd find yourself downshifting more often. Luckily you can fine tune things with the tire size to some extent.

Carl, knowing you as I do I do not expect you to agree but if attempting to accelerate a given mass against a standardized resistance, more power is always going to reduce the time needed and increase the acceleration rate. Simple physics there. That's step one. Step two is that a larger displacement engine of a given build type is going to produce more power. Admittedly there's some wiggle room here but not really enough to overcome the displacement advantage unless there are some very radical differences in the build. If it's the same engine, the bigger one will make more power. (Displacement is King) Therefore, more displacement equals faster acceleration. Those monster Hemi's are king of the dragstrip for a reason and you don't see any of them being destroked. I'm not sure how to be any clearer about it, but as we all know opinions will vary and we can believe anything we like. I prefer it that way actually. And of course 600 gram pistons and rods, 100 gram wrist pins, and an 11lb flywheel make all the difference in the world. So much so that I feel the aluminum flywheel is completely unnecessary on the street. But of course there may be some builds where it would seem right. Apparently such is the case with some of the more extreme B series builds.

Jim

Yes. more power will get one down the quarter mile faster (if it hooks up).  Does not always equate to revving faster.  Although, in your case, with lighter reciprocating assembly, it does.  A run of the mill, stock components Buick 300, don't think so.  Compare it to a short stroke Chevy DZ 302.

>Yes. more power will get one down the quarter mile faster (if it hooks up). Does not always equate to revving faster.

Well, see I have a bit of an issue with that statement. It seems to me that less elapsed time is the same thing as accelerating faster.

A given car/engine combo will within reasonable limits turn a rather standard range of engine revolutions in traveling the 1/4 mile, say something in the range of maybe 2000 revolutions given variations in gear ratios, tire size, tire slippage and driver launch characteristics. ( 24" tires=~800rev/mi x axle and transmission ratios / .25 etc, it can be calculated rather more exactly) That being the case, and engine rpm at terminal speed being dependent on elapsed time ie, vehicle speed at the finish line, the more powerful engine not only reaches a higher rpm but does it quicker. How is that not faster acceleration, and likewise how is that not quicker revving?

Inquiring minds want to know.

Jim

I don't equate how quick an engine can get down the drag strip to how quick it can rev or get from zero to redline.  A drag car stays near redline the whole trip.  I have a pneumatic drill that can go from zero to redline pretty damn fast.  Not so quick in the 1/4 mile.  

"A given car/engine combo will within reasonable limits turn a rather standard range of engine revolutions in traveling the 1/4 mile, say something in the range of maybe 2000 revolutions"

BTW, a Top Fuel dragster turns a smidge over just one forth of that.

Yep. Well, like I said, fortunately we can believe whatever we like. I do like a peppy engine. And it's not like we are pushing any hard limits here, just have to pay attention to the weight of the internals. Those parts are considerably heavier than they have any need to be.

Jim

Revisiting this discussion.  After a lot of hand wringing, I decided to pull the trigger on getting the TA heads.  Of course, with those heads (and my 6.32" Ford-style connecting rods), that drives a different choice of pistons.  I am still trying to avoid custom pistons, but after a lot of searching, I came across these Mopar V6 pistons: https://www.summitracing.com/parts/uem-3245c-std, which have a 3.78" diameter (in the standard size for these pistons), 1.283" compression height, and are flat top (no dish or crown).  They are *about* $275 for a set of eight.  My initial calculations with this piston and head combination gives the following result:  12.5 compression ratio (with a thin 29 thousands head gasket), 41 thousands quench, and a 1.64 rod ratio.  Anyone have any thoughts on these?  I do know I'll have to re-bush the connecting rods for the slightly smaller Mopar size. And is 12.5 compression too high?  I know there are more variables, such as cam, intake, and exhaust, but trying to establish a baseline for the other variables.  Thanks!

Eric, Way too high! You don't want over 10.5.  What is the ideal pin height, Maybe 1.26? Most figure .020 for steel shim and .040 for composite gaskets. For zero deck with the small chamber heads you can't use a flat top you need a substantial dish. I'll do some calculations and try to find something.

Eric, this first calculator shows ideal pin height for zero deck as 1.295. the second calculator shows ideal dish cc at 37.5 for 10.5 compression. Both for 3.85 stroke and 9.540 deck height and 3.78 bore.

http://www.wallaceracing.com/Calc-Deck-Height-rod-length-new.php

http://www.wallaceracing.com/cr_test2.php

Thanks Jim, I figured you guys would have a better perspective than me.  I'll definitely check out what you sent over.

Eric give these guys a call for custom pistons. We lucked out with Chris's build with off the shelf pistons. Specify 1.29 pin height, 38cc dish and .912 pin. If they can't do 3.78 bore you may have to go 3.8.
https://dssracing.com/

"Eric, Way too high! You don't want over 10.5. "

And you will still be running on 93 octane.

I am hoping I can switch to 87 with about 9.5:1 & an all aluminum engine.

Jim and Carl,

Thanks.  I should be able to get it down to under 10.5.  I actually *may* have found an off the shelf LS piston that may work, although I'm going to look into the link that Jim sent along.

I appreciate the help, as always.

GM 4.8L or 5.3L, no doubt.

IIRC the TA heads have about a 35cc chamber. At zero deck with a composite head gasket that means a 35cc dish gives you right at 10.5:1 compression.

Jim

Carl, you're correct.  GM 5.3.  The OEM LS pistons don't seem to have anything close to the correct configuration, but I found an aftermarket forged piston that gets closer to what Jim N. suggested:  https://www.summitracing.com/parts/dms-1803-3780

The compression height is a bit higher at 1.305" and dish is less at 15cc, but I calculated 10.43 CR and .033 quench with a .040 gasket.  Jim B. mentioned 35cc, but I've seen mention of opening up the TA heads to a volume of 54 cc, but not sure if that's correct.  As GM pistons, the pin size is different from the Ford rods I have, so I need to figure if it's OK to hone the existing wrist pin bushings a bit (from .912 to .927).  Also, if I calculate with a thicker .050 gasket, CR drops a to 10.2 with quench at .043.

With rings and pins, this set runs about $725.

As an aside, IF it's possible to open up the combustion chambers, I'm wondering what would seem to be better--a larger chamber with less dish, or a smaller chamber with more dish.  Either way, there's likely cost (either custom pistons or work on the heads), so it would be interesting to consider what I might get with the two approaches.