Big bore/short stroke, anyone try it?
Big bore/short stroke, anyone try it? I was reading another thread the other day about a 302 camaro that was done a while back. It was a destroked ls1. I brought it up in conversation with a friend of mine and it got us thinking about it. Has anyone ever tried taking a resleeved block and installing a shorter than stock crank to yield XXX CI? I imagine it would have the power of a stock CI motor, and rev WAY higher. I know that he pro5.0 mustang cars are destroked 351's, how would this work for an ls1? I imagine the heads woudl have to really have some real high volume, like the set that TEA just did on the afr casting, ( I think it was over 235cc or something ) to really work. If done right, it may be a 8000 rpm motor, maybe more? If there's anyone out there that has tried it, speak up, what was the findings?
I did close......went with a resleeved block, stock stroke, and the longest rod I could fit (came out 388). The engine revs like mad as is and it's still WAYYYYY out of tune. The stock engines (when forged) will spin well into the 7K range and my 388 could probubly get close to 8K.
I looked at doing the 4.8 liter crank which would destroke the 388 back down to a 350 but to me the extra 38CIs will do more than the RPM capability (9K RPM is a lot to build for
). 
I looked at doing the 4.8 liter crank which would destroke the 388 back down to a 350 but to me the extra 38CIs will do more than the RPM capability (9K RPM is a lot to build for
). Intresting. The 4.8 crank was the route I was thinking. What we were thinking is that the motor would spin up so quick, and to alot higher rpm level that it would allow use of alot higher rear end ratios, and if running FI, ALOT more boost. Example, most guys drag racing with a 28 inch tire usually runs a 4.56 gear, because they want the car to top out around 6500 to 6800 rpm. If you were to run something higher, like say a 4.88 with the same tire, that would put you around 7300 at the traps. I guess my thought is that a car running a turbo setup like that would probably be way better in the first part of the track because you could launch at a way higher rpm, and have the boost making alot more power sooner. I'm sure that there's a reason that noone's tried this, ( no replacement for displacement ) but I figured I'd throw it out there, see what other people think.
Originally Posted by JL ws-6
( no replacement for displacement )
true, but lots of boost helps make up for it...
I think the reason nobody has done it is because they are all going "why spend all that money on a smaller engine"
Originally Posted by 2001CamaroGuy
I think the reason nobody has done it is because they are all going "why spend all that money on a smaller engine"
When you start spending a lot of time above 7200 rpm, you want to make sure everything is light weight and up to the task too.
Ragtop, you see where I am going with this. A 90 MM fast setup, especially a ported one, or possibly the ls2, would flow enough air to feed a motor that runs over 8K I'd imagine that alone with the afr heads tea just did would be good enough to flow the #'s to go well past 8 grand. A small lightweight crank and rod/pistons would spin real good, and with the added bore, the cubes would still be in the 350's which I would thinkis enough. Imagine how much fun that would be on the street, a motor that you could rev past 8 grand. You could run 4.56's or maybe even more in a 6 speed car. Just imagine being next to a pesky cobra and throw a 8000 rpm rev at him, with a cogged belt blower setup and a real loud blowoff valve, .... I'd think that they wouldn't want to play anymore. Imagine the boost that you coul make if the motor would go to 8 grand too, you could run a pulley that's alot bigger and havealot less belt slippage problems too. I am seeng alot of possibilities here. Now, anyone out there with A check I could borrow to finance my little dream?
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Never thought of this, however your idea makes since.
Weird concept, but it could judt work.
Another benifit I could see would be for the guys that race in the catorigy setup for cars less then 360 cubic inches.
You could acturally have a all bore motor running a 4.8 crank and get get a lot more out of your combo then just a 347 build.
You would get more air from the heads, and might even beable to run a larger cam????
Well if I was made of money then I would consider it just to see this idea in action, but Im not.
Weird concept, but it could judt work.
Another benifit I could see would be for the guys that race in the catorigy setup for cars less then 360 cubic inches.
You could acturally have a all bore motor running a 4.8 crank and get get a lot more out of your combo then just a 347 build.
You would get more air from the heads, and might even beable to run a larger cam????
Well if I was made of money then I would consider it just to see this idea in action, but Im not.
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Verdad Gallardo Yes, the classes that have a cube limit could definately benefit. The larger bore would allow for larger valves and better flow, more power, etc. Yet another reason for someone to try this out. This would be a good idea for one of the sponsors to try out, too bad I'll never get any credit for the idea.
On The Tree
Joined: Nov 2001
Posts: 164
Likes: 0
From: Gold Coast Australia
The only reason to build a small motor is to comply with rules you race in.
Your little big bore motor will make much the same horse power as a bigger motor but it would make less torque.
Another downside to high reving motors is the expensive valve train you need to handle it....definately a solid cam and adjustable rockers, titanium valves, retainers, you would be replacing springs more often and the launches would be at a higher rpm making for either a nasty clutch or a large converter that would be less efficient.
If you build a motor build it as big as your rules or cube/wieght class allows.
Some friends of mine race in the small cube classes...one for intance runs a 302 cube SBC he launches @ 9,000rpm changes gears @ 10,500. Sure the thing sounds awesome but he brings @ least one set of valve springs with him to a meet and never races two meets on the same springs....food for thought.
Your little big bore motor will make much the same horse power as a bigger motor but it would make less torque.
Another downside to high reving motors is the expensive valve train you need to handle it....definately a solid cam and adjustable rockers, titanium valves, retainers, you would be replacing springs more often and the launches would be at a higher rpm making for either a nasty clutch or a large converter that would be less efficient.
If you build a motor build it as big as your rules or cube/wieght class allows.
Some friends of mine race in the small cube classes...one for intance runs a 302 cube SBC he launches @ 9,000rpm changes gears @ 10,500. Sure the thing sounds awesome but he brings @ least one set of valve springs with him to a meet and never races two meets on the same springs....food for thought.
Idon't thnk that rotating mass and valve springs have much to do with each other. My thought were that a higher revving motor coud have a wider uasble power range for street and track use, it may be more versatile. Something that you could drive around on the street, shifting like a normal street car, but would have the rev's and power to go long with it when you want to take it to the track. Something that would allow you to take ful advantage of the 6 speed, where you could run a 4.56 or 4.88 gear and just use the 5th and 6th gears more. I know that my car on the highway in 6th gear at 90 is only turning about 2K withthe 3.42 rear. I figure that at 65 in 6th gear wit 4.56's it would be around 2200, still not terrible. Also, the heads and valve sizes that could be used would be very large for a low CI motor, so the power band would probably be alot larger than normal. Follow where I am going with this?
On The Tree
Joined: Nov 2001
Posts: 164
Likes: 0
From: Gold Coast Australia
Originally Posted by JL ws-6
Idon't thnk that rotating mass and valve springs have much to do with each other. ?
Originally Posted by JL ws-6
My thought were that a higher revving motor coud have a wider uasble power range for street and track use, it may be more versatile. ?
Originally Posted by JL ws-6
Something that you could drive around on the street, shifting like a normal street car, but would have the rev's and power to go long with it when you want to take it to the track. Something that would allow you to take ful advantage of the 6 speed, where you could run a 4.56 or 4.88 gear and just use the 5th and 6th gears more. I know that my car on the highway in 6th gear at 90 is only turning about 2K withthe 3.42 rear. I figure that at 65 in 6th gear wit 4.56's it would be around 2200, still not terrible.
To have a small motor that would make the same horsepower as a bigger motor it wouldn't be near as friendly to drive.
Originally Posted by JL ws-6
Also, the heads and valve sizes that could be used would be very large for a low CI motor, so the power band would probably be alot larger than normal.
Originally Posted by JL ws-6
Follow where I am going with this?
For the same money a bigger motor will be nicer to drive less, maintenance and kick a small motors *** at the track.
TECH Fanatic
Joined: Mar 2003
Posts: 1,112
Likes: 0
From: Dallas
Originally Posted by JZ'sTA
Another benifit I could see would be for the guys that race in the catorigy setup for cars less then 360 cubic inches.
You could acturally have a all bore motor running a 4.8 crank and get get a lot more out of your combo then just a 347 build.
exactly
I think someone should do this.
I understand that the higher port velocity that is associated with larger heads and valves will have to be revved to make power, but it's not like the motor would have to idle at 2 grand to run. I guess a single valve is heavier than the 2 smaller ones found in dohc motors,so it does take more work to open/close the valves. All theory aside, I still think that someone should try it, we can ponder what it would do all day long, but unitl someone throws it together and tries it, we do not have solid test info as to the results. I think that this type of setup would also take well to boost, as the larger heads that could be run would flow the added air rather well, and being a lightweight rotating mass motor, the spool time would be considerably less than a standard motor with the same cubes, power would probably come on really quick. Again, no solid proof of anything, but would be intresting to see the results, a setup like this compared to a standard setup.
On The Tree
Joined: Nov 2001
Posts: 164
Likes: 0
From: Gold Coast Australia
IF you were running in a class that calls for 360 cube max you may find a benifit with the unshrouding of the valves but this would be the only scenario that you would go to the expense of building this motor when for the same money you can build a bigger one.
I have driven that 302ci LS1 Camaro, and I have kicked around this engine approach.
I bought a 4.8/3.27 stock crank but recently threw it out since nobody would buy it.
It could work great in a CI limited racing class.
I bought a 4.8/3.27 stock crank but recently threw it out since nobody would buy it.
It could work great in a CI limited racing class.
Good, someone on here that knows what he;s talking about that was thinking that this could possibly work. PSJ, how did that car seem at lower RPM, did it feel dead, or still o.k.? I assume once it got over 6K that it started to really pull hard. Too bad you chucked that crank, I would have happily took it off your hands, rahter than see it go to a scrap yard.
Quote:
Originally Posted by JL ws-6
Something that you could drive around on the street, shifting like a normal street car, but would have the rev's and power to go long with it when you want to take it to the track. Something that would allow you to take ful advantage of the 6 speed, where you could run a 4.56 or 4.88 gear and just use the 5th and 6th gears more. I know that my car on the highway in 6th gear at 90 is only turning about 2K withthe 3.42 rear. I figure that at 65 in 6th gear wit 4.56's it would be around 2200, still not terrible.
"Actually it would be closer to 2700...still not terrible."
JL was correct: 65 mph is 2200; 2700 rpm would be 90 mph.
The high revving motor may make less torque on the street, but you are running a lot more gear (4.56 vs 3.73 or 4.10s for the typical modified street car). If you're willing to use higher shift points then the typical V8 shift points in daily driving, in town driving should be fine. It just may seem wierd at first using the extra revs; almost like driving a 4 cyl sports car. As long as the oil consumption is under control, I could see this working if this is what you wanted to acheive.
Personnally, I like sticking with the stock crank and going bigger bore with the goal of a 7000 rpm street machine with 4.10s.
Originally Posted by JL ws-6
Something that you could drive around on the street, shifting like a normal street car, but would have the rev's and power to go long with it when you want to take it to the track. Something that would allow you to take ful advantage of the 6 speed, where you could run a 4.56 or 4.88 gear and just use the 5th and 6th gears more. I know that my car on the highway in 6th gear at 90 is only turning about 2K withthe 3.42 rear. I figure that at 65 in 6th gear wit 4.56's it would be around 2200, still not terrible.
"Actually it would be closer to 2700...still not terrible."
JL was correct: 65 mph is 2200; 2700 rpm would be 90 mph.
The high revving motor may make less torque on the street, but you are running a lot more gear (4.56 vs 3.73 or 4.10s for the typical modified street car). If you're willing to use higher shift points then the typical V8 shift points in daily driving, in town driving should be fine. It just may seem wierd at first using the extra revs; almost like driving a 4 cyl sports car. As long as the oil consumption is under control, I could see this working if this is what you wanted to acheive.
Personnally, I like sticking with the stock crank and going bigger bore with the goal of a 7000 rpm street machine with 4.10s.