ABeasst

iTrader: (5)

has anyone in here done a turbo 302ci LS1? I figure you can rev it higher and use say a 76R or ITS80R with awesome reults. Any thoughts on this?

v8bug

for a 302 I would imagin you would have to start with a 4.8l since it has the shorter stroke.

Now here is the problem, the stock 4.8 rods would only work to a point, so if it is a serious build you would want better rods. Problem is no aftermarket manufacturer that I know of makes a rod long enough (factory is 6.276) So you would have to go with 6.1 or 6.125 rods. But now where are you going to get pistons that would work with that stroke and a shorter rod? I don't know either?

The other problem would be the piston bore. I have looked and looked to see if anyone makes forged pistons for a gen III around the stock 4.8/5.3 bore of 3.780, and found nothing, nata. so you would have to bore it to around 3.898 or something, which will take you over 300ci.

If anyone has any ideas I would love to here some!, I think it would be killer to have a high reving turbo monster. I mean I am sure it can be done, although it would probibly cost a ton of $.

By the way, Is there anyone out there that makes forged pistons around the 4.8/5.3 bore of 3.780? or do those motors pretty much have to go to the ls1 bore for better pistons?

Pro Stock John

iTrader: (34)

I once toyed with the idea of a such an engine, I would have used the 4.8 crank and a 6.200 or 6.250 rod. In the end, there is no advantage to having this little engine.

ABeasst

iTrader: (5)

you could turn the **** out of it and run a smaller faster spooling turbo to make some serious power.

Pro Stock John

iTrader: (34)

Don't get mad at my response... But your post is vague. Why would a 302ci make more power than a 346ci LS1? Heck, is a 346ci LS1 even the best 'small' engine to run with a a turbo setup? They are just numbers. First off if you rev a 302ci, what rpm would you take it to, 8000? You would need solid roller parts or some semi-fancy hydraulic stuff. Seems like the cost would be higher then for the smaller engine.

Now it's true that with turbos, you have run into backpressure issues, where the exhaust can't handle the pressure from the engine. That's one of the reasons that some of the Supra folks have gone to GT55 hybrids. They are running these bigger turbos because they are seeing huge backpressure. They are boosting 40psi.

I'm not overly concerned about engine size, I would be more concerned about the rpm limits of the valve train you are proposing.

My hydraulic 346 could probably take 7500, but I know it can safely take 7200.

ABeasst

iTrader: (5)

I'm not mad

Pro Stock John

iTrader: (34)

No I meant I didn't want you to get upset at my view.

KraZy

iTrader: (4)

There was a lot of discussion from V8 DSM guy. It was a very interesting read, but over my head.

Pro Stock John

iTrader: (34)

I don't have the link for it, but there was a good thread where folks discussed the 302 stuff. But in the end, the 302's were built for homologation reasons, for a racing class.

So my challenge to you is, what does a combo like this accomplish? Why is it better to have a combo that has to run higher rpms? Seems like higher rpms just lead to valvetrain parts failures.

I think if you create an example, ie. goal of hitting 800rwhp, which combo works best?

You'd have to decide what the parameters were, like the gas.

If you assumed 93 pump gas, I would do a big stroker. If you assume 104 unleaded, I would do the cheapest combo that would work.

A 302ci example would not have an advantage over a stroker or a stock style 346ci.

GrahamHill

iTrader: (6)

Why would you want to take away the torque in an engine intended for a generally heavy car?

ABeasst

iTrader: (5)

the goal is to be able to use a smaller turbo so you wont have the lag of a T88 for say 900rwhp. a 302 w/ a T76GTS should be able to make 900 and spool a little quicker than a T88. I prolly wouldnt do this setup but it just popped in my head over easter.

KraZy

iTrader: (4)

Would the faster rev's offset the turbo's like for load?

y2khawk

iTrader: (5)

A small motor does have it's advantages. You can get away with a smaller turbo in some cases, IE one that has a tall/narrow compressor map. small displacement gets you high PR for given flow, and you can use that to your advantage.

Small motor, high rpm also reduces BMEP. The "bomb" is simply smaller, so you don't get the cylinder pressures a large bore motor would have. Spin it to make the HP, and your headgakets will like you

For an all out racecar, it might be an interesting exercise. But for a street/strip car, you just beat up your valvetrain trying to get there. I'm talking 8's or quicker range BTW.

just remember 5.0 mustangs are 302's plenty of those around that are "fast"

my .02

Whistler

iTrader: (46)

What's BMEP?

97blkz

iTrader: (1)

I've seen the destroke to 327 with FI and they made good numbers with +7K rpms!

Pro Stock John

iTrader: (34)

For completeness, the definition of BMEP is: the average (mean) pressure which, if imposed on the pistons uniformly from the top to the bottom of each power stroke, would produce the measured (brake) power output.

Note that BMEP is purely theoretical and has little to do with actual cylinder pressures. It is simply an effective comparison tool.

If you work through the arithmetic, you find that BMEP is simply a multiple of the torque per cubic inch of displacement. A torque output of 1.0 lb-ft per cubic inch of displacement equals a BMEP of 150.8 psi. So a very practical way to calculate BMEP is:

BMEP = 150.8 x TORQUE (lb-ft) / DISPLACEMENT (ci)

y2khawk

iTrader: (5)

Wow, John knows how to google

http://www.epi-eng.com/ET-BMEP.htm

Brake Mean Effective Pressure, and the above about sums it up.

But, it's got more connection to cylinder pressures than you'd think.

FUroundeye

iTrader: (6)

See, that's what I don't get about a short stroke motor in a boosted application. It seems like it would be a disadvantage b/c A) the loss of displacement means you would have to spin it higher to spool the turbo (which I guess is sorta offset by the fact that you can extend the rpm range, so maybe you would see full boost over the same total rpm range that you would in a longer stroke/larger displacement motor), and B) I'd think you'd almost have to run higher cylinder pressures to achieve the same power levels. A longer stroke allows you to delay the point at which you make peak cylinder pressure, which means you can make more power off that same pressure. I'm really a novice when it comes to all this, so take that for what it's worth. I'm sure the higher RPM help in other ways that I'm not fully aware of, but it seems like the trade-offs mostly offset each other.

andereck

Cylinder heads appear larger to a smaller displacement engine allowing the smaller engine to produce its power at a higher rpm. Smaller engines are generally also more fuel efficient when under cruise as they don't take as much to feed. The big tradeoff is that to produce power on par or better than the larger engine you will have to rev it higher and or compress the air more. Higher air compression, or boost, will cause the temperature to rise above that of the larger lower boost engine which may and probably will cause it to detonate or spark knock sooner even though the mass airflow rate of the two engines may be the same. This wouldn't be a case for a smaller compressor section of the turbo as you will need to move the same amount of air.
Small cubic inch engines are for fuel economy first. When racing is the issue build the largest one you can to get the job done reliably.

QWKSLVR

Helluva copy/paster too!!