https://www.thirdgen.org/forums/engi...t-fiction.html

That thread really doesn't answer this question. I also did a search, but... I am hoping I can get a STRAIGHT FACTS ANSWER on this. I don't want to hear about seat of the pants, what "feels" better, or how many you have or used to have. Just straight facts.

Ok, Assume I build 4 identical engines in the 300-325 HP Range with the only difference being the crank/stroke: 302, 327, 350, 383. What would be different between them?

Max HP, Max Torque, RPM range. HP/Torque curves?

 

All things being equal, camshaft, heads, intake, carb, compression ratio etc. Bore makes more HP. Stroke makes more torque. Bigger engines however will want more cam, head etc so they're generally make more power.

All those engines use the same 4" bore except the 383 which has a slight overbore. Each increase in stroke will make more torque. HP increase will be minimal with the displacement increase if all other factors remain the same. A camshaft that makes good power in a 302 will be very mild when put into a 383. The same camshaft will still make the same amount of HP but the increased stroke will let it make more torque.

 

Awesome!! This is exactly what I was looking for. Thanx!!!

 

For the past decade or so my thoughts have been if the main caps / crank comes out ... It becomes a stroker (383/+) ... Not much $$$ vs the gains on a FULL rebuild.

 

You can't fairly compare the gains of the stroker crank versus the recovered loss of power from a rebuild. Fresh to fresh, the stroke should always add 40 ft-lbs. I've seen it add more, all the way through the powerband. I've also seen a TPI 350 beat a built carb'd 383, and a TPI 383 beat a built carb'd 454. But stroking is cheaper and easier than converting to TPI. 325 HP 302 SBC vs 325 HP 383 SBC? The 383 will make more average HP, but peak at a lower RPM. Gear both to do 100 MPH in the 1/4-mile at the RPM of peak HP, there won't be much difference, because the stroker loses to taller gearing, and it loses to internal friction. Build both with the same heads, cam, intake, and headers, assuming a typical street build like Vortecs with an XE268H, the 383 will totally annihilate the 302.

 

Again, Thank You!!! These are the type of answers I was looking for!!

 

I think we are saying the same thing ... BUILD a stroker ! With parts matched to the c.i. ... Nobody puts the same cam into a 350 & a 383 unless they want to leave HP & TQ On the table

IF you plan on running a TPI setup instead of a old school dual plane w/ carb ... Prepare to be dissapointed above 4800~ rpm, unless you go with an aftermarket type of "TPI " (Super Ram / etc.)

 

Most certainly the 383 is going to have a lower broader torque curve given a cam to compliment the stroker and a cam that in a 350 that would be radical would be more accepting in the larger 383 engine.

 

With all things NOT being equal, any engine should be able to produce 1 HP per CID if proper components are used. The 383 should be able to produce 81 more HP than the 302.

 

Not sure if it was mentioned but same cam heads intake may produce same power on all those motors with same bores just different strokes, but the rpm it peaks at will drop as stroke increases.

Xe268 cam may peak in the 6500 rpm range on a 302, but same cam in 383 will peak by 5500. Theres alot more torque available and thus you dont need to rev up as high so you use less gear and converter. Thats the "driveability" thing but thats a topic of much debate.

383 with more cubes has potential to make more hp than all of them but needs more head and cam to feed it compared to the rest. It always makes sense to take cubes when you can for street builds. The torquey power curve has its advantages.

But theoretically, if you have same car and swapped 302 that made 350 hp with the vortecs and 268 cam, and also had the 383 making 350 hp with vortecs and 268 cam, then both would run same times IF you geared and stalled them right because the 302 doesnt have power in the low end so it requires more gear and stall.

 

I do think a consideration for this thread should be made for over square engines:

http://en.wikipedia.org/wiki/Oversquare

 

Too much stroke could be a bad thing. Piston speeds and ring packages on short piston heights would be a concern. Rod stroke ratios too.

I know a guy with a 4.03"/4" bore stroke motor that ran hard for many yrs on spray no issue but id never consider putting 4" stroke in a 350 block. Great for tpi motors looking for torque tho. Low rpms keeps things safer as far as piston speeds go.

 

They all share the same bore, with the 383 being a 0.030" overbore from the stock 4.00".

302: 3" stroke
327: 3.25" stroke
350: 3.48" stroke
383: 3.75" stroke

And two other stroked 350 variants:
396: 3.875" stroke
409: 4.00" stroke

If you are going to assume 325hp, each one would have a different TQ reading, TQ peak, HP peak, RPM range, and "area under the curve".

As an example, a 325hp 350 might peak at 5000rpm; a 325hp 383 will be lower at say 4500rpm; a 325 hp 302 may peak at 5800rpm, and a 325hp may peak at 5400rpm.

Then you have the TQ curves, which in the 302 is going to peak at a much higher rpm and be of lower total value than the 350 or 383. You might have a 4500rpm TQ peak in the 302 and the 383 might be at 3000rpm. Obviously we all know that hp is TQ * RPM, so you can see that the power curves in the larger motors start quicker and taper off more quickly.

I want to point out that the smaller motors have the advantage of using a longer rod than the longer stroked ones, a 302 can use a 3.25" rod and get a rod/stroke ration above 2.0, where a 350 with a 6" rod is around 1.72. Nothing realized in a 325hp motor, but in a high RPM screamer, it is an advantage.

As other have mentioned, each sized motor will have an optimal cam profile and may also require a different head. I would not want to put a 200cc low velocity head on a 302, where a 383 might work best with it. Volumetric efficiency is another thing to think about - a smaller motor can possibly generate a better efficiency at a given HP level as there may be a "bump" due to the higher RPM (a guess).

 

But what creeps into decisions on which engine is the logic of dollars and cents. A smaller engine to gain the same output as a lager one is going to cost more or equal to the larger one. It then become a question if a class racing requires the smaller engine. We know that a well equipped parts wise 383 costs the same as a 496 BBC and a LS engine. That the 496 BBC has only a wt greater of 75 lbs.(aluminum head).

We need to recognize the natural attributes of each size engine and build off that. A example of that is a 383 with a big fat middle torque curve which is a prime candidate for a nitrous shot as long as it is built to handle it.

 

My engine is slightly over square with a 4.625" bore and a 4.375" stroke. That puts it at 1.057, A 383 is 1.066 which is more over square than my BBC yet people still keep building them.

 

Practical results nearly always must outweigh theoretical issues. 383 isn't ideal on paper, but the ease, the availability, the affordability and the power per dollar means the 383 will remain popular for several years yet. Let me take another angle: If the goal is 500 HP, at the lowest final cost, there's a stronger case to be made for a turbo EFI 305 than any 383 with no boost. The 305 will cost less to build, the cost is the fuel system and the Chinese hairdryer. But the MPG will be better, the driveability will be better, and the emissions will be cleaner. The only thing going for the 383 is that it's easier to figure out and package.