Engine and Transmission Tech

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.



Edited 1 time(s). Last edit at 11/24/2022 12:06AM by MGBV8.

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: [www.summitracing.com], 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!



Edited 1 time(s). Last edit at 02/20/2024 11:59AM by Airwreckc.

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.

[www.wallaceracing.com]

[www.wallaceracing.com]



Edited 2 time(s). Last edit at 02/20/2024 02:00PM by mgb260.

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.
[dssracing.com]



Edited 3 time(s). Last edit at 02/20/2024 02:41PM by mgb260.

"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: [www.summitracing.com]

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.



Edited 3 time(s). Last edit at 02/21/2024 10:36AM by Airwreckc.

And I found an old post from Jim B (to me). suggesting that opening up the TA heads is the wrong idea. So, it may be custom pistons after all.

"My opinion is that opening up the combustion chambers is the wrong way to go, and for a couple of very good reasons. It may cost you a few hundred more to do but if you are considering the purchase of TA heads you can afford the alternative. And it eliminates probably over 20 hours of labor so if your time is worth more than say $20/hr it is worth it.

If you open up the chambers you lose any squish area the TA heads give you, reducing fuel efficiency and making the engine more prone to "ping" etc. Might just as well sit the pistons down further in the hole, the effect is much the same and is much easier to do.

You would also basically be destroying what are originally a great set of heads. Some may disagree, but really the heads are not the issue and neither is the combustion chamber. The real issue is the pistons. And if you are considering heads that will cost a bare minimum of $1600 even without valves and springs, it only makes sense to pony up the bucks for good pistons. If you do that the manufacturer will make the dish whatever you want it to be so why mess around with counter-productive work on your biggest investment in the engine? My last two sets of custom pistons from Wiseco, bought this year cost me $1100 a set and that was through my local machine shop. You may find cast pistons that won't work for as little as $200 a set but they won't be right for the heads and the engine. You may find forged pistons in the $400-600 range but to match bore, pin size, compression height and dish volume to what you need is going to be very difficult, time consuming, and likely ultimately unsuccessful. You can easily spend enough time on the quest to make the Wiseco pistons look like a very attractive option.

Now, if you've gotten this far, especially if you have the 350 crank and the ex-nascar rods, the next thing is the roller cam. From TA that's going to cost somewhere around $500. The lifters can be aftermarket Chevy at about $400 a set and you'll need a cam stop, so figure that as a $1000 option. By this point the engine cost is approaching $5K if you do most of the work yourself and you should be somewhat adverse to screwing up that size of an investment. So in terms of head work try to be a little more conventional. Sure, if you like, fit nice valves and springs and clean up the bowl areas a little. But remember what this engine is going in, a sub 2500lb car. You can be quite conservative and still have extremely good performance. There is no need to go all-out unless you will be racing it against similarly equipped cars and for the most part the guys in this group have nothing there left to prove. With that combo and a mild cam you should still be comfortably over 300hp, well into the muscle car range.

Which is why I mentioned starting out with the 4.0/4.6L heads. I just grabbed a set from the local pick-n-pull for $150 and the engine was pretty clean inside and had only a quite small ridge in the cylinders. I expect that with new seals I could use them as they are. I plan to use them on my 340 when it goes back together. It means I have to cut the piston dishes deeper but they are thick enough to do that. Then if I later feel a need to bolt on the TA heads it is a simple swap. The set of 300 heads can then go on the stock 300 (mule) and I'll have a set of low mileage iron heads that the Buick guys will likely be interested in.

Yes, you would be correct in thinking that this means I have 3 engines for my car, which does seem a little like overkill even for me and eventually I may let one or even two of them go. OTOH, once I've finished playing around with them the spares won't be eating anything and if I go out and abuse the engine in the car as I am somewhat inclined to do occasionally I won't need to be too concerned about it if there's another on the stand ready to take it's place. The other thing is that this whole scenario is evolving. The 340(350cid) Eaton blower equipped long rod engine was great. With the TA heads it would be even better, but I've retired that intake because it is too tall and won't work with the 300. The next intake will be built for the 300, specifically with the blower dropped down into the lifter valley but I've only just started on that. And nobody knows how long the flat tappet cam in the mule will last. So the 340 will go back together with the Rover heads and a stock (iron) 4bbl intake that will accept the intake system currently on the mule. That gives me more time to build the intake and blower/accessory drive. I do like having a spare available at a moment's notice and also having an engine available for development work. It's really the only way this works out that will allow me to always keep the car driveable."



Edited 1 time(s). Last edit at 02/21/2024 10:53AM by Airwreckc.

Eric, I used 29cc for the Rover head in my calculation. Corrected to 37cc I get 10.43 with a 30cc dish.. DSS wants $629 for their standard forged pistons. I wonder how much more for custom?



Edited 3 time(s). Last edit at 02/21/2024 12:04PM by mgb260.

DSS already have a piston with 29cc dish, they would just have to change pin height to 1.29 and pin diameter to .912, if you went 3.8. Might not charge too much extra for that. Be nice to go down to 3.78 bore size.



Edited 1 time(s). Last edit at 02/21/2024 12:05PM by mgb260.

Thanks Jim. I just emailed them with that very question. I'll report back when I hear something.

As an aside, I did my calculation at 1.295 pin height, 35cc for the CC and 35cc dish, resulting in about 10 CR.