Destroked Small Block?

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Certainly one of the most interesting discussions on the forum in a long time. So many of you guys are straight up encyclopedic. :cool:

As @autoxcuda and others have pointed out, this is not the best dollar:performance approach but the thing that occurs to me in an era of 32v /460 crank hp 5.0L, 11 second 1/4 mile times in the basic 2018 stock Mustang GT, trying something totally different with old tech is the best way to keep our old cars fun and interesting. The idea of de-stroking a small block, coming up with a valvetrain, head and rotating assembly that can use/handle, make power at 7k+, sounds like the bee's knees to me. :cool:

I recall that piston speeds in a performance gasoline motor are typically 60mph at redline or so...is that right? Are there motors out there which can handle piston speeds much higher than that? At what point does energy required for accelerating the piston back and forth begin to become counter productive?
 
Now your really asking about science!
Since I can not answer this in that manor though I have read about things like “Ultimate Piston Speed” and other things, I would say that the easiest method would be ether where you run out of money (LMAO!) or if your unlimited fund account found an area where the engine just doesn’t make anymore power on the dyno.

There is a point. Where that point is, IDK. I have seen (& heard) some badass engines turn some wild rpm.

Actual piston speed can be found out from a calculator on line. Mostly in feet per second. The longer the stroke the faster the piston speed vs a shorter stroke engine at the same rpm.

My grandfather in law worked at Chrysler with Shelby in the early days of the turbo projects. He would tell me stories of turning ridiculous rpm and the dyno showing zero HP & Tq. Something A lot of the conversations I had with him I still do not really grasp 30 years later.

Grammar
 
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There are some high winding "small" block V-8's in the mid 200 to low 300 cu. in. range that can rev 10k+. The smaller & lighter the rotating assembly, the higher & faster it can turn. But there are other limiting factors. i.e.: valve train stability, cam specs, port size/shape & durability. I read a long time ago that in classes where cars were classed by weight to cubic inches - like a car has to weigh 10 lbs per cubic inch of motor - a 300 cu. in. engine has to be in a car weighing 3,000 lbs., it was easier to go faster by going smaller with the engine (up to a point). The reason was overall efficiency. It's easier to go faster with 300 cu/in @ 3000 lbs than with 500 cu/in @ 5000 lbs. Old Pro Stock and Modified Production classes were perfect examples. They were destroking the Hemis to be more competitive before the across-the-board 500 cu/in rules took effect and the Modified Production cars of the '70's & 80's really sang. Today's Comp Eliminator classes and some SS classes have some of those cars. Some are 4 & 6 cyl and very light.

A little history:



 
Yes yes yes! I remember that. I was a kid during those years.
I remember reading somewhere on line a fella (or 2 or 3 or....) destroking there engines to 300 or less cubes and turning wacko rpms for power. These engines are currently out there right now running the tracks. There in super light cars or rails.
 
Locomotions' explanation of why people destroked engines is spot on. In 79 some friends ran a Camaro in C/SM that had to weigh 10 pounds per inch. They had a .030 over 302 which is 305, they got a different crank to take it down to 295 inchs so they lost 100 pounds which helped. Ran 6:50 gears in a 9 inch, would come off the line at 10,000 rpm.

Used to love to watch modified eliminator cars run back in the late 70s early 80s, a lot of small inch engines with 5 speeds and 6 something axle ratios coming off the line at 10,000 plus rpm, wheels up at 1-2 and 2-3 shifts. Back then people ran cable drive mechanical tachs with a telltale needle, you could look at peoples cars after a run and see the needles up sometimes above 11,000 rpm.

At the nationals in Indy in 80 there was a guy out of Kentucky named Don Bowles, I think he owned coal mines, he obviously had money and and had a first class operation. He raced a Fairmont in modified eliminator, used Roush engines and had Jack Roush himself there working on his car. Somewhere I have a picture of Jack changing the valve springs, the tach telltale needle was up at 11,700 rpm.
 
[Qi have a 2.96 stroke moldexUOTE="rumblefish360, post: 1971917454, member: 1189"]Yes. The reason to destroke an engine is to fit into a cubic inch limit class. This is mostly found in NASCAR with there 355 cid limit. There are some drag racing classes that limit engine size by cubes. The rules that I have read in the past were small blocks to *** size, big blocks to *** size, etc... but that was stroking up. The old Trans Am racing series had a 5.0 liter limit.

How you get the cubic inches long s a matter of bore and stroke and there is nothing in the rules about you having my to (must) run a certain configuration.

MoPar used to sell destroke cranks for this purpose. 1 such kit was to destroke a .030-360 engine down to a 352. Currently Mancini racing has these forged cranks on sale. You’ll need a custom piston. Mopar had forged slugs for this.

The ability to rev high is mostly a valve train stability & valve spring issue. Not so much the cranks stroke. The idea of a shorter throw on a crank needs less time to cover the distance so yes, it revs quicker. If everything else is equal. A shorter throw on a crank coupled with heavier rods and pistons will not move as fast (or easy) then a longer stroke crank and super light rods and slugs.

I have a destroker crank, rod, ring and slug set from MoPar. If I get a suite able block to run it, I will.
i have a 2.96 stroke moldex crank for sale,destroked 318 diamond pistons,a 70 318 block if anyone is interested,was going to destroke a 318 to a 288[/QUOTE]
Are items still for sale ??
 
i have a 2.96 stroke moldex crank for sale,destroked 318 diamond pistons,a 70 318 block if anyone is interested,was going to destroke a 318 to a 288
Are items still for sale ??[/QUOTE]
Send him a PM. He hasn't been online since Apr 22 of this year. He may get a e mail notification for a PM if his settings allow.
 
just an novice here but is'nt this the reason for the trans am racing// chevy 302, boss 302,AMC 290/304 and didn't mopar destroke the 340 ???!!!
 
just an novice here but is'nt this the reason for the trans am racing// chevy 302, boss 302,AMC 290/304 and didn't mopar destroke the 340 ???!!!
They had a cubic inch rule to LIMIT power output.....that's why the 340 had to be destroked, to meet the max cubic inches rule.
 
and Pontiac
I worked on the Mopar (which evolved after) and the AMC which was supposed to use a 4.060 260 block but we used a 4.25 Nascar block and a short crank
some comments
GO LIGHT ON THE PISTONS using old TRW forgings makes a slug, use a modern cam- the old 340 cam will be gentile up to a certain rpm but will not make horsepower
it's all about cylinder heads no mater what the cu in
I'm with Stroker Mc Gurk
Our second AMC said 360 in the side of the block and was supposed to be 304 like the main motor but was actually 427 inside- Same as Hayden Proffits Grant Piston Ring Blown Fuel Funny Car
the actual horsepower was not that much different- now torque below max HP was an entirely different story
The cubic inch rule did not really limit power output with the same heads
it did save transmissions
 
Good info, and to add clarification, a small cubic inch engine CAN make as much power as a larger one, but will require more RPM to do it...
 
Just weighing my options
Destroked
Stroker
Etc
Either way I go its going in a early model 318 Block
Im trying to hort up some old good ones.
 
Certainly one of the most interesting discussions on the forum in a long time. So many of you guys are straight up encyclopedic. :cool:

As @autoxcuda and others have pointed out, this is not the best dollar:performance approach but the thing that occurs to me in an era of 32v /460 crank hp 5.0L, 11 second 1/4 mile times in the basic 2018 stock Mustang GT, trying something totally different with old tech is the best way to keep our old cars fun and interesting. The idea of de-stroking a small block, coming up with a valvetrain, head and rotating assembly that can use/handle, make power at 7k+, sounds like the bee's knees to me. :cool:

I recall that piston speeds in a performance gasoline motor are typically 60mph at redline or so...is that right? Are there motors out there which can handle piston speeds much higher than that? At what point does energy required for accelerating the piston back and forth begin to become counter productive?
Old school technology and recipes will never go out of STYLE .
When its all said and done most of us folks are not making a living with our engines so its all for personal preference etc , I have always liked the unusual stuff and my Henry J Gasser will be know different if u want it easy and BORING go Chevy small block I could have done that real cheap but im not like the Masses I guess I fell out of the highchair on my soft spot to many times as a child !!!!
I have perfected the Art of Wasting Money .
 
Good info, and to add clarification, a small cubic inch engine CAN make as much power as a larger one, but will require more RPM to do it...

I doubt that to be true. If that was the case how come the mountain motor IHRA pro stock cars were a good bit quicker and faster than the 500 inch limited NHRA cars. IHRA guys even generally had a good bit less money typically to throw at those motors.
 
What are your intentions for the build?
High Winding
Small Block with this Jerico.

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what was the destroked 340's actual cid in trans am ?
 
where's the cage?
Mountain Motors also make more torque/HP Below peak HP and may not make quite as much peak HP due to being less efficient, friction etc
"The only thing that beats cubic inches is more cubic inches" Stroker McGurk
 
where's the cage?
Mountain Motors also make more torque/HP Below peak HP and may not make quite as much peak HP due to being less efficient, friction etc
"The only thing that beats cubic inches is more cubic inches" Stroker McGurk
Cage coming doing suspension now
 
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