Destroking an Engine

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MuuMuu101

MuuMuu101

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I was just curious if there were any potential benefits or disadvantages of destroking an engine. I know by destroking an engine you give up some of your lower power for more top end. Does it also increase your rpm limit? Do you think it will have any effects on driving fuel efficiency? Is there a way to do it to our mopar small blocks? Thanks for your knowledge.
 
not many oppertunties to destroke a small block chrysler...certainly with oem cranks....putting a 3.31 crank in a 360..is a option...but with the cost of spacers and line boring the mains...the cost gets stupid...

unless you need a certain specific cubic inch engine for a class...do not anything gained...to get the shorter stroke the same deck height block...you will need a longer rod or piston with larger compression height with increase the weight of the rotating assembly...
 
The only reason to ever destroke an engine is for some sort of class racing limitation. Less stroke does not automatically = more RPM, and not sure why you'd want that.

The lower the RPM you can make power is just that much easier on "blowed up parts."
 
What is the objective? Fuel mileage in an A-Body?

318 with some sort of proper quench heads, quite mild cam which operates perfectly at the rpm range based on your driving speed vs. rpm, heat cross-over operational on a performer intake, small diameter tube headers, quadrajet or TQ, 4 speed OD with 3.23 rear end gears. Lighten the car where possible, lower it to reduce wind drag, run narrow tires to reduce rolling resistance, drive 20 foot behind a semi tractor trailer at all times.

What engine and trans and rear end gear ratio are you working with now?
 
There are instances where it works for certain racing classes. The most successful would be the old DZ302 Z28 Camaros. Those things flew for their time. Ford sort of did it with their Boss 302s. The Mopar 383 winds up super fast. (at least that's been my experience compared to my 440s).

Didn't the AARs and TAs run destroked 340s?
 
There are some minor advantages to running a higher rod ratio engine dealing with less bore wear and a slight increase in mechanical advantage. Although Mopar LA engines are already high rod/stroke ratio engines.
 
Rice Nuker said:
What is the objective? Fuel mileage in an A-Body?

318 with some sort of proper quench heads, quite mild cam which operates perfectly at the rpm range based on your driving speed vs. rpm, heat cross-over operational on a performer intake, small diameter tube headers, quadrajet or TQ, 4 speed OD with 3.23 rear end gears. Lighten the car where possible, lower it to reduce wind drag, run narrow tires to reduce rolling resistance, drive 20 foot behind a semi tractor trailer at all times.

What engine and trans and rear end gear ratio are you working with now?
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It was totally a theoretical question. I was thought maybe a smaller stroke would give you better fuel economy on day to day driving and then when you'd want to really have fun you'd crank it up to 6000+ hp if needed be (possibly adding a turbo to work on the higher end). But if it makes a difference, I've currently got a 273 that has low compression in one cylinder (may need some head work if I didn't destroy anything else, yet), a 904 transmission that seems to be fine, and a 7 1/4 rear end with open 2.94 gears.

This summer, my plan is to build up my 8 3/4 in the garage (Dr. Diff, bbp, new carrier with an Eaton TrueTrac, bearings, etc.), install bbp discs on all four corners, and install my Hotchkis TVS. However, this will make my engine the weakest link and most likely to blow up first.
 
Revhendo said:
There are instances where it works for certain racing classes. The most successful would be the old DZ302 Z28 Camaros. Those things flew for their time. Ford sort of did it with their Boss 302s. The Mopar 383 winds up super fast. (at least that's been my experience compared to my 440s).

Didn't the AARs and TAs run destroked 340s?
Click to expand...

Chevy 302s were not "destroked" they were simply a 283 punched to 301 ----as we called them---done by many a "back yard" hotrodder before Chevy did it out of the box.

The reason the Mopar TAs were destroked was for the reason I already mentioned----that race class, at the time, had a CID limit (was it 305?), and Ma had nothing to compete, otherwise, unless they re-worked the 273.

-----Which brings up the question----why'n 'ell did whoever write the T/A rules pick the CID limit, anyhow?

Also, this nonsense about an "engine revving faster" is just that. The thing that makes an engine rev is the HP it produces and the gearing it's against. If you put a (short stroke) 265-283-302 into something that was geared high, and heavy, the damn thing won't rev, put a trailer behind it!!!!

The big big thing (other than optimum crank angle 'n fancy stuff) is that long stroke engines generate high piston speed, so that is a limiting factor.

It might be "cool" to have something rev to 8500 but if the long stroke guy producing more HP blows by you at 5500 you haven't gained a thing.
 
Well said. Mopar engineers were miles ahead of the other manufacturers when it comes to engine design. Don't try to over engineer a build. It has all been tried before and if it was a great idea everybody would be doing it. Take a look at the stroker program. Someone figured the combo and it worked. everyone is doing it with great success. The destroked program only worked because it had to, in certain classes of racing that limited cubes. The power band was raised by a couple thousand rpm. The combo didn't make more horsepower and usually less torque. Efficiency and RPM doesn't go hand in hand. It requires a combo of select components to make it work correctly. tmm
 
The concept of "de-stroking" mainly falls into class racing requirements limiting engine displacement. Build a smaller engine to race in a particular class. Chevy did it in the Z/28s by putting a 283 crank in a 327. Whala, 302!
So why not use a smaller bore w/ a longer stroke you might wonder? Engine builders most often prefer an over-square bore to stroke ratio, meaning larger bore than stroke length. A lot of things come into factor here. Piston designs, air flow & ram effect into the cylinders, valve positioning, block preparation, & so on. There are mostly advantages in the higher RPM ranges as its been mentioned. Doesn't necessarily mean it will rev faster, but would produce its peak power at higher RPM. Depending on the intended application that is what they're looking for. Racing is about accelerating through the whole course as fast as possible & being able to maintain the amount of power to produce enough RPM for high MPH at the top end. Whether it be drag racing or at the end of the straight away in Nascar or circle racing. Big bore/ short stroke = higher RPMs & tighter powerband. Now you gotta have gears etc to match. Higher numerical rear end & close ratio transmissions. Not always practical for street driven cars. That's why we like our strokers. They give us lots of torque at lower RPMs & hopefully less broken parts.
 
67Dart273 said:
Chevy 302s were not "destroked" they were simply a 283 punched to 301 ----as we called them---done by many a "back yard" hotrodder before Chevy did it out of the box.
Click to expand...

I know all about them punched 283s, but the wolf has it right. The DZ302 was a destroked 327 (283 crank). They were also nothing similar to the later 305 or 307. Just sayin.
 
Moldex 2.96 crank in a 340 got Mopar 305, enough to slide in under the CID limit. They still show up from time to time on Racingjunk. Dont know what they used for rods or maybe a tall piston? I guess you could call the Boss 302 a destroked 351C but you'd be wrong although they used the same head, and I heard both Chevy and Fords big head 302's would almost stall when the door was opened, cause the dome light would cause enough drag on the alternator to stall the no low end motors. That's a Chevy joke.
 
The 302 was not destroked. The Chev, 302 was a regular production engine (67-69) of 302 cubic inches. People always toss that "DZ" stuff out there but "DZ" was just the code for a 69 302. 67 -68 302s were code "MO", but you never hear anyone say MO302....

The only reason it was ever built was to meet Trans Am requirements. But, it was a 302 from the factory and offered in a production car.

For something to be destroked, it would have had to start life as something bigger. The 302 was never bigger than a 302. Destroking was not allowed in Trans Am until 1970.

Now the 305ci engines ran in the Challenger TA and AAR Cuda (Trans AM race versions), were destroked 340s.
 
the first year chevy 302 was a 2 bolt main ,small journal crank ,like some one else said 327 block/283 crank, the next 2 years they went to 327/350 large main engines with 4 bolt caps, and a special large main crank made with the 283 stroke ground on it. chevy was ahead of every one for the trans am project.
 
teringer said:
the first year chevy 302 was a 2 bolt main ,small journal crank ,like some one else said 327 block/283 crank, the next 2 years they went to 327/350 large main engines with 4 bolt caps, and a special large main crank made with the 283 stroke ground on it. chevy was ahead of every one for the trans am project.
Click to expand...

Chevy produced their 302 and Ford already had their 302. Trans Am really didn't care about Mopar.
 
MuuMuu101 said:
It was totally a theoretical question. I was thought maybe a smaller stroke would give you better fuel economy on day to day driving and then when you'd want to really have fun you'd crank it up to 6000+ hp if needed be (possibly adding a turbo to work on the higher end). But if it makes a difference, I've currently got a 273 that has low compression in one cylinder (may need some head work if I didn't destroy anything else, yet), a 904 transmission that seems to be fine, and a 7 1/4 rear end with open 2.94 gears.

This summer, my plan is to build up my 8 3/4 in the garage (Dr. Diff, bbp, new carrier with an Eaton TrueTrac, bearings, etc.), install bbp discs on all four corners, and install my Hotchkis TVS. However, this will make my engine the weakest link and most likely to blow up first.
Click to expand...

A 273 will hold up fine and you can get great mileage at the same time. Just build it like any other High Performance motor and run a Thermoquad or Quadra-jet carb. No need to destroke it.
 
The 302 Chevy discussion is amusing as the 301 was a bored 283. I do not know the cylinder wall thickness of a 283, but it sounds scary to me. I do know that it was done routinely back in the day. The 302 was a destroked 327. Used to do it all the time, using the factory 283 steel crank in a small journal 327 or the 307 cast crank in a large journal 350 block. It is all semantics. A 302 generally would rev quicker and higher than the 350, assuming the same heads and cam. So your thinking was generally correct, but we don't have the factory cranks, pistons, or rods to destroke Mopar engines economically.
 
I've long wanted to build a de-stroked Ford small block. My thought behind this was fairly simple, Any given port has a max flow rate. Take a medicore flowing head and put it on a smaller displacement and suddenly it's not so mediocre. (BTW this is why I've no interest in a 225, I'm sticking with the 170 slant.) As a bonus you'd gain rod ratio, but that has to be watched as you can go too far. In the case of the SBF the 289 has a 2.87" stroke so I was thinking somewhere in the 2.25"-2.75" stroke range. Use the common as dirt 2V Cleveland heads to build a pseudo "Boss 250" or something. No idea what I'd ever put such an engine in (Locost 7 maybe?), so the idea is still just that.
 
If someone really wanted to destroke an engine, the Chrysler part number for the 2.96" crank is p4452974.
 
They where back in 70's in Modified production class , for a example I had 1966 chevelle that ran ran F/MP and we where only able to have so much cubic inch to weight. I ran 301 cu in small block a 327 with 283 crank. Now I launched it @9000 rpms had 50lb flywheel and 6:17 gears with a 3.31 first gear in a 4 speed trans.
 
And here I was thinkin to destroke something, you had to grind the crank shorter.
 
[ame="http://www.youtube.com/watch?v=TZ7rAqjXr_8"]1978 NHRA Sportsnationals - YouTube[/ame]

Here check this out , this is way I use to drag race
 
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