What would you build if limited to 372ci - with boost as an option

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33IMP said:
For a street car, or drag car, I probably wouldn't bother.
For a salt car, I would assume you would have to do anything possible for durability sake.
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For this discussion, I was looking for everyone's input on what to build to get below 372ci. It isn't a deal breaker if it just doesn't make sense, but lessening a record by 20mph is huge.

Is my math right? If so, it seems doable for a displacement regulated class.
 
You had better talk to your crank guy about that .275 destroke. I'd bet you can't cut it that much.
I think the most you could destroke it, and still use a bbc rod is .205, and that's if the crank grinder is perfect.
To destroke more than that, you'd have to use something else, maybe a long small block rod. I don't think you can find a small block rod long enough, unless you go to a custom aluminum rod. And the crank would be seriously thin, if it doesn't already have a "window".
 
33IMP said:
You had better talk to your crank guy about that .275 destroke. I'd bet you can't cut it that much.
I think the most you could destroke it, and still use a bbc rod is .205, and that's if the crank grinder is perfect.
To destroke more than that, you'd have to use something else, maybe a long small block rod. I don't think you can find a small block rod long enough, unless you go to a custom aluminum rod. And the crank would be seriously thin, if it doesn't already have a "window".
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Another option. Take crank down 3.21 and use chevy rods which are 6.535. 364 inches from a 383 and off the shelf rods. Just need factory piston with 990 pin
 
About 50 years ago, when nhra was playing around with car weights in prostock (to make sure the chevies won, and mopars didn't, just like today) there were destroker cranks available for Hemis, to make smaller than 426 engines, so the car could,be lighter.
Good luck finding one. I think there might have been two strokes available. I remember 366 and 396 hemis in prostock.
 
I think you are trying to use shelf pistons. I just don't think that is remotely possible, cause I think your 3.21 crank solution is not possible.
I think step one would be to assume you will need custom pistons for anything you put together to work at 371 (or less).
 
33IMP said:
I think you are trying to use shelf pistons. I just don't think that is remotely possible, cause I think your 3.21 crank solution is not possible.
I think step one would be to assume you will need custom pistons for anything you put together to work at 371 (or less).
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I would assume custom also at this point.
 
33IMP said:
That would theoretically need a 1.84 compression height piston, according to my math. What is the ch of the pistons you want to use?
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My motor is a 68 which should have the 1.920 CH positive deck pistons I believe.
 
All measurements theoretical blueprint specs, but.....
1/2 c4ank stroke (depending on if you think it's 3.38 or 3.375) plus a 6.358 rod, ppus a 1.92 ch piston comes out to 9.965. So theoretically .025 in the hole with a 9.98 deck.
Of course, ALL of those dimensions can be off, from crank grinding, deck cutting, or over-height deck from Mopar, to reconditioned (shorter) rods.
 
71GSSDemon said:
So, a 383 has bore of 4.25 and stroke of 3.375 and 6.358 rod.

Reduce stroke by 0.275

So destroke to 3.1 and use BBC rods measuring 6.635. (Eagle H beam shelf stock) This is a 0.002" difference from stock current piston pin height, yes? So a 383 piston with a 0.990 pin should work for 351ci?

Or the 400 bore of 4.342 and get 367"

Please let me know if I am wrong.
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Where did so that put the pin in the piston.
 
71GSSDemon said:
Sorry, what are you asking?
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Sorry, I read that wrong. That is a very long piston was my point.

There was always an issue with Chrysler stuff and the tall decks relative to stroke length verses GM garbage.

Not only do you end up with a long piston for equal displacement you end up with longer pushrods.

If you are trying to be competitive with relatively short stroke engines you need to consider things like pin height and pushrod length.

If it’s class racing then RPM matters. Long pistons and long(er) pushrods (compared to other engines and their architecture) make it that much harder to get rpm.

I know (going off my memory) a 3.313 stroke piston has a 1.85ish pin height.

At 7500 everything looked good as far as the piston was concerned. At 8000 the skirts would look a bit strange like I was running too much clearance. We started beating up ring grooves too.

So I decided to tighten up my piston clearance. Sneaking up on it you could feel it starting to grab the pistons.

So I adjusted the clearance a bit looser but decided 8500 was better (it was and still is better) and then you could see the piston rock beating up the tops of the bored.

So I went to .043 rings and gas ported pistons to try and save the ring grooves from getting beat up. I could never get the clearance where I wanted it.

Class racing isn’t cheap. Competitive class racing is expensive and labor intensive.

I just want you to think about how one thing (like destroking) can and will affect many things. Sometimes things you may not know until you get the engine built and then you end up like my dumb *** buying more pistons than I wanted to.

Chrysler made this short deck small block for a reason.

If you are trying to compete with equal displacement engines with short strokes and you have a 9.5 deck and the other guy has a 9 inch deck (my numbers are just for discussion) you will have a hard time being competitive.

If you get competitive and then someone gets more rpm you are screwed again.

Someday I’ll recount a AS/GS legal story I have. Because that very thing happened. I just happened to be with a car at the track when the dude running more rpm showed up.

It was exactly what I’m saying here.
 
Newbomb Turk said:
Sorry, I read that wrong. That is a very long piston was my point.

There was always an issue with Chrysler stuff and the tall decks relative to stroke length verses GM garbage.

Not only do you end up with a long piston for equal displacement you end up with longer pushrods.

If you are trying to be competitive with relatively short stroke engines you need to consider things like pin height and pushrod length.

If it’s class racing then RPM matters. Long pistons and long(er) pushrods (compared to other engines and their architecture) make it that much harder to get rpm.

I know (going off my memory) a 3.313 stroke piston has a 1.85ish pin height.

At 7500 everything looked good as far as the piston was concerned. At 8000 the skirts would look a bit strange like I was running too much clearance. We started beating up ring grooves too.

So I decided to tighten up my piston clearance. Sneaking up on it you could feel it starting to grab the pistons.

So I adjusted the clearance a bit looser but decided 8500 was better (it was and still is better) and then you could see the piston rock beating up the tops of the bored.

So I went to .043 rings and gas ported pistons to try and save the ring grooves from getting beat up. I could never get the clearance where I wanted it.

Class racing isn’t cheap. Competitive class racing is expensive and labor intensive.

I just want you to think about how one thing (like destroking) can and will affect many things. Sometimes things you may not know until you get the engine built and then you end up like my dumb *** buying more pistons than I wanted to.

Chrysler made this short deck small block for a reason.

If you are trying to compete with equal displacement engines with short strokes and you have a 9.5 deck and the other guy has a 9 inch deck (my numbers are just for discussion) you will have a hard time being competitive.

If you get competitive and then someone gets more rpm you are screwed again.

Someday I’ll recount a AS/GS legal story I have. Because that very thing happened. I just happened to be with a car at the track when the dude running more rpm showed up.

It was exactly what I’m saying here.
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Thanks, just remember this is for Bonneville. 5 miles of getting to speed, little traction, heavy car, skinny tires, etc. Speed markers are at 2.25, 3, 4, and 5 mile marks. Displacement, fuel type and car modifications dictate classes. I am ok with boost on my 383, but record looks better for less than 372ci.
 
71GSSDemon said:
Thanks, just remember this is for Bonneville. 5 miles of getting to speed, little traction, heavy car, skinny tires, etc. Speed markers are at 2.25, 3, 4, and 5 mile marks. Displacement, fuel type and car modifications dictate classes. I am ok with boost on my 383, but record looks better for less than 372ci.
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Yup. And were I building your engine I’d be worried about piston length.

Can you ballpark an appropriate rpm the cars in your class run?

Since you want to reset a record I’m assuming you want to be competitive so that’s why I was explaining why tall decks and short strokes cause issues you might not have thought of.
 
Newbomb Turk said:
Yup. And were I building your engine I’d be worried about piston length.

Can you ballpark an appropriate rpm the cars in your class run?

Since you want to reset a record I’m assuming you want to be competitive so that’s why I was explaining why tall decks and short strokes cause issues you might not have thought of.
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of, sorry. It is all over the map. Depends on your set up. I had pictured a 6500rpm engine with boost. Maybe it would last a while, vs 8000rpm. Hp and gearing. So, if using a 28" tire, 2.5:1 ratio with a max at mile 4 and sustained for 1 mile
 
I feel you got to know what other guys are doing in that class to try to beat a 28 year old record. Even if the goal is more about experience then ultimately beating the record it still helps to know what you are competing against to help make decisions. Especially how much hp is required.
 
Actually

Screenshot_20241002_143258_Chrome.jpg
 
Newbomb Turk said:
Yup. And were I building your engine I’d be worried about piston length.

Can you ballpark an appropriate rpm the cars in your class run?

Since you want to reset a record I’m assuming you want to be competitive so that’s why I was explaining why tall decks and short strokes cause issues you might not have thought of.
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So, Turk,, would you run a longer rod and shorter piston, or whatever height of piston that works with the short (or, shorter) rod?
A .030 over 383 block with a 3.23 stroke crank,and a 6.800 bbc rod, needs somewhere around a 1.5" ch piston, depending on the deck height of the block.
371.7 cubic inches.
 
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71GSSDemon said:
of, sorry. It is all over the map. Depends on your set up. I had pictured a 6500rpm engine with boost. Maybe it would last a while, vs 8000rpm. Hp and gearing. So, if using a 28" tire, 2.5:1 ratio with a max at mile 4 and sustained for 1 mile
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Ok, if you can do what you want at that rpm I’d be ok with your big block example above with one caveat.

That would be the pistons would be coated by Line2line so you can keep the piston as square in the bore as you can. It makes the pistons last longer and it helps with ring seal and ring life.

At that rpm I wouldn’t be nearly as concerned about piston height.

I’m liking the BB options better now.
 
33IMP said:
So, Turk,, would you run a longer rod and shorter piston, or whatever height of piston that works with the short (or, shorter) rod?
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I would want the ring pack to not be compromised and I wouldn’t want the rod to stroke ratio be much higher than 1.70 or lower than 1.55 and only that low if he has unlimited induction or power adder.

That’s kinda where I’m at. I try to limit the compromises as best I can.
 
Newbomb Turk said:
I would want the ring pack to not be compromised and I wouldn’t want the rod to stroke ratio be much higher than 1.70 or lower than 1.55 and only that low if he has unlimited induction or power adder.

That’s kinda where I’m at. I try to limit the compromises as best I can.
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.... and using a stock block in a situation such as this is a big compromise.
 
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