I was just thinking that you could take a 302 and make it a 327 by using a 400 block, and get a lot more power. Does any company make a kit for this? Has anyone done this?

 

That "kit" would be spacer main bearings, a 400 crank, and short rods or rods and pistons for the 3-3/4" stroke. Unfortunately, the combination you suggest would net 377 cubic inches, not 327, and it is a fairly common non-factory conversion.

 

This is going to seem so obvious that it's apparently easy to overlook.

You don't "get more power" by taking a big motor and making it smaller. You get more power y taking a small motor and making it bigger.

Therefore:
If you started out with a 302 and added 1/8" its bore by replacing the block, you wold get more power. On the other hand, if you started out with a 400 and made it smaller by removing stroke (or bore), you would get less power.

The only reason to do this sort of thing is if you are racing in a class where you are CID limited. In such a situation you might get slightly more power from one bore/stroke combo that produces the spec CID than from some other combos that result in the same CID.

Many people have done that sort of thing. They always come out with less power than they old if they had built a 400.

The above post is completely wrong. You don't use bearing spacers to put a 3.75" stroke crank into a 400 block; you just use a stock 400 crank to do that, and of course you come up with a 400. You would use bearing spacers to put a shorter stroke crank into a 400 block. If you did that with either of the remaining large-journal 302 cranks, you'd come out with a 321. This would of course make far less power than a 400; more than a 302 though. It would be a waste of a good block and a highly valuable crank.

 

I'm not sure what Merlin's reply means. (Edit: And RB beat me to the response.)

A 302 has a 3" stroke. The main bearings are a smaller diameter, so bearing spacers would be needed, true. But, with an assumed .030"-overbore, the displacement comes out to 325 cubic inches. 6" rods would be easy to do with 302/305/350 journal sizes, but of course special pistons would be required.

It's been done. It would make approximately 6% more power than a .030"-over 302 would. But, if you have a 400 engine that needs a .030"-overbore and the crank turned no more than .030" undersize, you'd have a 406, which will make a lot more power than a 325; ~25% more. Even if the crank had to be turned down to 350 journal sizes (which is how the whole 383 thing got started in the first place), you could use the above-mentioned bearing spacers & 350-journal-size rods, still have a 406, and make that same 25% more power than a 325. Or, if the 400 crank is completely trash, you could put a 305 or 350 crank in it and have a 377, which would be about 23% more powerful than a rebuilt 302.

There is really no reason to de-stroke a 400 if you don't have to. You won't make more power by decreasing displacement; you can't make it up just because it will "rev to the sky" (which you can make a 406 do, anyway); physics just don't work that way.

 

wow.

i found a thread where theres some fact and some mis-info in every reply.






:lala:

 

if you want a 327, i have one for sale.

 

Build the biggest engine you can afford.

 

the 302 used a 4" bore with a 3" stroke...in 67-68 they had small journal mains and in 69 they had large..all 302's were 4bolt main..never made a 4 bolt main 327...the 400 is unlike any of the above the 400 has a large main journal..larger than the 69 up SBC...and it used steam holes in the block.. a 4.125 bore and 3" stroke would be a very high fast reving engine but would make low torque...why bother tq gives ET hp gives MPH

 

I have a 352 chevy sitting in the garage on a stand where we can pre run engines(made out of the botom of a grocery cart..haha). Hooked a radiator and a baterry tray, along with 2 guages and power and start button.....

its a 400 block (.030 over) and a 327 crank yeilding 352 ci Chevy. It uses J&E pistons, 6.125" Eagle H-beams, Eagle 215cc heads Compcams 255 dur @.50 with .575 lift on a 110.....

It revs like crazy!!! throttle reponce in a destroked motor is Phenominal! I should find a digital cam and record it....whats a good site to host movies?? Ill post a pic for sure and try to find a digi cam with a bigger memory card....mine only has 8mb =(

 

'68-up are large journal.

Not true.

 

What is it with people wanting to de-stroke an engine???

Even the Honduh guys don't do that.

Then there's the "but you get better MPG with a smaller motor"
Not true if you want the same power output.

Case in point...

My wife drive's a 1993 MX6 with 2.5L V6 with a 5spd. It's rated at 164 HP @ ~ 6500 RPM. My 5.0L V8 makes 6 more HP at half the RPM.

Her car get's ~23 mpg city/highway combined and mine gets ~22 combined. WHY? Because my car cruises 70 MPH @ ~2000 RPM. Her car revs about 3600 RPM @ 70.

The best part... Her car ran an ET of 16.8. My car ran an ET 16.5.

Do you think it would be a good idea if I took a 3.25" crank out of a 307 and put it in a 267 block (3.5" bore) to make 250 CID engine???

Maybe if I put it in a Honduh..... :lala:

 

RB is correct. I had that one completely screwed up. It gets pretty cloudy at 3-something A.M., so I probably shouldn't even be posting (or surfing).

I knew there were some petential crank main journal size issues between 2.45" and 2.65", and had the bores and strokes all screwed up. The other problem that I hinted at was the rod length differences and piston pin heights. Using a 302 could result in some main journal problems, depending on whether the 302 was a "true" 302 or a 283 crank home conversion, as so many were.

Using Vader's engine calculator, the combination yields 320.7 CID. Still not 327, but not 377 either. I was thinking about the old .030-over 400/350 crank combination, or at least thought I was... Then there's the 350/400 no-bore conversion good for 377, oh, never mind...

Sorry for the misinformation

 

And I never said my calaculator was 100%, either. It rounds some of the values, but is usually close enough for argument's sake.

IOncidentally, a 400 SBC does use a 2.650" main journal, while other SBCs used a 2.300" (early) and 2.450" (later) main journal. A 400 crank is going to have a helluva time squeezing into a smaller case, so you'd better have a really good torque wrench. A 400 would require spacer bearings with any other SBC crank (except aftermarket). The SBC-III engines are halfway better with 2.559" (65 mm), and the LT5s got it right with 2.76" mains.

 

Destroking an engine is desirable when high RPMs are favorable to your driving(drag racing)

Stroking a motor brings the usable rpms down, while destroking (larger bore/smaller stroke) moves the powerband up to the top end...

Strokers= Lower HP/more Torque motor good to about 6500 RPM
Destrokers= Lower torque and more HP when you get up over 6500 RPM.

Ive been in a 302 that does 8500-9000 RPM. Its insane....

 

WHAT?!?!?!?!

I give up...

 

does this help???

Assuming were drag racing....

Stroking will get you off the line fast using lots of torque, and run out of uuumph at higher speeds

Destroking will get you off the line slightly slower because of lost torque(but can even get off line faster bc less chance of losing traction) but will be a lot faster once you get the car over 6500RPM..

or maybe this will be better...

Stroking can kind of be like running a stock TPI to 6500RPM, pointless it stops making power 4000-5000rpm...

destroking is like changing the same motor to a carb and adding duration to the cam......the car is making power in higher RPM, not just spinning the motor fast and making no power)

(and some strokers can run higher RPM, i know. Im just trying explain what the differences between stroking and destroking are

 

I understand why you think this, but it's not correct.

Hypothetically.....

While your busy getting your 302 PAST 6500 RPM, I'll have gotten my 383 up to 6500 [b]3 times[b] and cross the finish line.

 

not a drag racer?

by the time you get your car up to 6500 then shift....4500rpm.... 3 times with slower throttle reponse...

Ill have my destroked motor up to 8000rpm quickly and be shifting and still at 6500 on shifts and still pulling hard and fast...

anyways, not to argue.... I have run both and top end is where I like it.....

and (from earlier) ricers dont destroke because they dont have anything to start with lol they can already turn 7000-9000rpm...

 

OK.....

So what you're saying is if I build a 383 to spin to 8000 RPM, and you build a 302 to spin to 8000 RPM, then you'll win?

I'm gonna stop now. I'm getting a severe headache trying to understand your logic.

And that's NOT a sarcastic statement. I really am getting a headache.

 

No, i would build a 377(or 383 if i went .060 over) I wold start with the biggest bore i could...

oh yeah, NASCAR uses the same setup as I used on my new motor, 400 block, 3.25" cranks(327 size) but .060 over instead of my .030

and so do those pro drag trucks, thinking of the Summit S-10s that run 6's, and leave the line at 8000rpm

I just did it to try it, its not in the car yet, most only destroke the 400 with a 350 crank making a 377...i jsut went one step further with a 327 cranks, and really long 6.125" rods

 

if you want the basics of why the destroked concept is .. different..

when you decrease the stroke you are removing mass from the rotating parts and reducing the amount of travel that the remaining mass has to go through.

when you do this you are reducing the amount of energy in the rotating structure at any given rpm and hence the amount of work to get it there.

simply put you are making the drivetrain rotational mass lighter.

HOwever you are also reducing displacement which would decrease work output per revolution.

I think most of the reason for the small stroke large bore in racing is for reduction of drivetrain mass and reduction in stress levels in the con rods and bearings at the rpms they run (9000 nascar 18000 F1)

 

Wait, wait, wait...destroking reduces mass? How so?

It does decrease piston velocity. Since momentum is 1/2MV^2, reducing that squared velocity has a significant effect on reducing momentum (note that only the velocity is squared, not the mass).

Think about it: at 6000 RPMs the crank is turning 100 times a second. Since each piston has to stop twice per revolution, the rotating assembly has to stop each piston 200 times per second. Momentum makes stopping harder. Overcoming piston momemtum requires using power that you're trying to produce.

THAT's why shorter strokes are favored by sustained high-power users.

To say nothing about the stress factors involved in overcoming that momentum.

 

Wow . I guess I need to read more to stay current. The last tiem I saw NASCAR engine rules, the bore was strictly limitied to 4.000" +/- 0.060", and similar stroke restrictions were in effect, with a baseline stroke of 3.50". Then again, that was well over a month ago.

 

When you are rules-limited, you do what you have to within the bounds of those rules. Carbon-carbon and titanium go a long way in such situations, but I haven't heard many questions on this board about where you can get the best prices on that kind of stuff.

Shoot, the losing teams in that crowd do things most of us have never heard or dreamed of. And spend the kind of money on one engine most of us would be happy to net in a year.

But, you knew all that.

 

well I guess it doesnt have to reduce mass but theoretically your polar moment of inertia of the crank should go down along with the rod and pistons because they are now closer to the center of rotation and hence require less force to rotate them.

 

Minor compared to reducing the speed of the linear mass, or reducing that mass.

 

I never said it was any huge benefit

Stop one upping so early in the morning -- it doesnt become someone with that many posts (or maybe it does)

 

everything i have ever read stated the 302's were all 4 bolt main, with forged crank and only came in Z28's...when was a 2 bolt 302 used ?

 

Just cause I'm a nerd.... Kenetic energy is 1/2*M*V^2
Momentum is M*V

David

 

Does anyone in here speak english?

 

No Hablo Espanol. ^