With the same setup, as far as h/c and such take it, the larger motor should be faster bcuz of what was said earlier about power under the curve. The hp/ci effeciency is going to drop with a bigger engine all with the same setup, but the largest should go the fastest bcuz of power under the curve. Guys with a 350 LT1 making 400rwhp are in the 360-385rwtq range, one guy I saw uped that displacement to 360 cu in and suddenly he was at 400rwtq with a smilar setup as a 350 but without loseing hp. Sure his hp/ci went down, but does that mean the car will be slower? NO, it should be faster.

If I was looking at effeciency, I would be looking at tq/ci, I would think that would give you a better idea of what the motor is capilable of.

 

For a larger motor to make as much hp, you have to remove the restriction..... in other words, the bigger stroker is gonna need alot of cylinder head and an intake that doesn't cost you in airflow. That's why alot of race engine guys stick to some of the smaller displacements... so they can get enough cylinder head on the motor to turn more revs.
Tq/L is all cool and fine but there's only so much torque you can make anyways. Let's say its 1.55 lbs-ft per cid. So you have the choice to make your 1.55 lbs-ft/cid at 4500 rpm or make it at 5500 rpm..... one will make quite a bit more hp than the other. One will also be quicker at the track than the other and it aint the lower reving (lower hp) one. So you make as much torque as you can but to be the fastest at the track, you place that peak higher in the rev range and gear the car accordingly.

-Mindgame

 

Well said Mindgame!

 

Then a better effiecency would be avg hp/ci wouldnt you think?

Yes a larger engine should make more power given larger heads and/or cam, but given everything the same they should all make roughly the same hp except that the larger motors will make more tq. Larger engines just have more potential to be "unlocked" with larger h/c.

 

Avg Hp/Ci would be good but with the same set of heads that equations goes down the more cubes you add. Well at least there is a point of diminishing returns like every curve.

Say 1.5 ft lbs per cube and 1.75 HP per cube. That's 530 ft lbs and 610HP on a 350. Then a 383 is 575 ft lbs and 670 HP. You need alot more cylinder head for that. 610hp is nothing to sneeze at but 675hp doesn't just happen because of the cubes. It's possible to do both but they are entirely different engines.

Mindgames point is good, but remember that RPM cost $. A 6K engine is easy but a 8K engine is going to cost some money if you want it to live. RPM kills things in the engine. A cube class all depends upon the engine designer. Smaller cubes and max power are going to cost you the same as a big cube engine making alot of power and tq, but the small cueb engine might be better because of things like weight. It all comes down to Lb per HP and traction. If you give me the same heads and less weight I'll take the smaller cubes, because of RPM potential and Lb per HP.

Most of you guys aren't talking about a max effort drag engine though. Nobody wants a 10,000rpm engine that you have to change the valve springs in every run and makes over 2.6 HP per cube, well at least on the street.

Guys, cubes are cheap to a point. On a LT1 a 383 is cheap and is never going to be overstressed on a street/strip application so why go to a 7500rpm 355 when you can have a stronger engine that's a 383? It's all going to cost you some cash anyways.

Bret

 

Not to mention the fact that on the street, torque is key. Your car will be fastest if you build your motor to be strongest in the RPM range where the motor will spend most of it's time during a run. So on a street car, I would say building a car with over 6000 RPM peak power is probably not necessary.

 

It is really cool to see my thread alive and well over 6 months after it started. It seems like we have struck a chord here.

A little update on my engine progress. I originally posted this topic starting in late Sept last year. On the first Saturday of October our car club had a dyno day where we all ran to see how the summer mods had improved our cars. My car is a bone stock long block! That includes the 120,000 mile stock cam. I dynoed 343 rwhp/ 356 rwtrq. Not bad for a stock 350/m6.

Now for the fun part. On the same dyno three 383s (2 LT1s and one carbed) pulled much worse #s.

The best one was 360hp, the next best was 318hp, and the saddest was 275ish hp.

Both the LT1s were cammed (the 360hp had the cc305).

What was the difference between my engine and their strokers? I believe they were seriously undercammed and needed much more head work. I did some serious home porting over the summer that totally woke up my combo. Their heads obviously were not up to the task of filling up a stroker.

I am more convinced that unless you go with very well built top end parts you can't extract power potential out of a stroker like you should. Plus for those of us limited to factory intakes, there is ounly so much cfm that you can get them to flow without boost.

I also am leery of building too much torque. Too much torque = no traction. No traction = no acceleration. I would rather sacrifice a little torque down low for additional midrange torque and high end hp. It give me a better top end charge and better control/consistency on launch.

BBB

 

Hey Jordan and Mindgame I agree with you guys that there are hyd rollers turning 7500 rpm, but the original question stated that he wanted to keep his CC306 cam right, so I don't think he'll make 7000 + rpm without a hydra rev kit or something. Especially in a 383 or 396 without a big head like AFR 220 or 227 fully ported and then the stock intake or 306 would probably become the restriction.

 

speak for yourself

 

I don't know where you get your definition of efficient either. Used car salesman trying to sell you a Metro

In most automotive circles, you know the SAE types, efficiency refers to specific output. In other words, HP per liter/cid.
On the other hand, since you brought up gas mileage, sounds like you're thinking of economy.

Thanks for the opportunity to help clarify your confusion

 

 

Efficiency is output/Input... Right???

If both cars weigh the same and to do the same one needs less fuel than the other to have the same HP which is more efficient????

The S2000 could be more efficient per CI, but that is it...

 

I think you've been reading too many of Trey's posts


That was my point exactly. Read my original post again. You basically disagreed with something we agreed on in the first place.

 

Thanks; that's what I thought you'd say.

 

Yes, Mindgame has a good point and although it seems to be more geared towards racers, much the same is true on the street.

"Torque is king"

Where have I heard that before?
Of course it's "king" but the question is, torque where? You have to look at more than the engine for that answer. If you want torque off idle, for pulling boats, small houses, whatever. Then stay with short period camshafts or build engines with as many cid as you can afford. Even then you are giving up potential horsepower for a small degree of durability.

If you are building a street engine that peaks at 6000 rpm then you are giving up some 1000 rpm of potential power. 7000 rpm is a reasonable rpm limit for any street engine given the correct valetrain componentry and attention to buildup tolerances. The 434 in my 4th gen revs to 7000 makes over 700 bhp, idles like a well tuned CC306 LT1 (350 cid) and is minimal maintanence... I check the valve lash every other oil change.

So, build the biggest engine you can afford and know what your goals are before you get started.

Take care