Building a F/I motor, stroke vs bore and cubes
07-08-2004, 06:17 PM
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Building a F/I motor, stroke vs bore and cubes Ok, so I'm totally rebuilding my motor in my ss camaro, I want to build it based on a GM 6.0 Iron block and I also wanted it to be big CID. I noticed that all of the Lunati stroker kits pretty much cost about the same price so whats the difference when building a F/I motor between say a 383 and a 447 CI stroker?
And of course the next question is how does a F/I car react to bore instead of stroke.
And finally, if some people could make suggestions or post their 6.0 Iron block setups I would like to see what your running including bore, stroke, heads, cam, etc?
And of course the next question is how does a F/I car react to bore instead of stroke.
And finally, if some people could make suggestions or post their 6.0 Iron block setups I would like to see what your running including bore, stroke, heads, cam, etc?
07-08-2004, 08:08 PM
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1. Is it going to be a turbo or a supercharger?
2. Limit overbore to the minimum.. You need a thick wall to maintain cooling, block strength and a good ring seal.
The 383 would have wider powerband than the 447.
I honestly think you could make more power peak power on the shorter stroke... You will probably not be too far behind peak numbers with a 6.0 and have alot wider a power band.
For the turbo motor I'm working on I looked at a number of real world chevy turbo dynos and picked over the specs and results.. I also played with different engine combinations on desktop dynos... Just like the real thing they are only as good as the operator..
I ran looked at various strokes 3.0, 3.25, 3.48, 3.562, 3.75, 3.85 etc... I also looked at bores from 4.0 to a motown 4.2 or so....
I'd just run a minimal cleanup overbore and the stock stroke... You can't really get dramatic results from bore increases due to the limitations of the block and the fact that it just wont run as cool, be as strong or have as stable a ring seal...
It is less expensive and spending time and money on changing the displacement wont reap the same benefits as time and money on getting the cams, heads, intake and exhaust just right...
This is for a turbo LT1 yet the thinking carries over. Like I said alot still depends on the head and cams but every stroke and bore combination has its own effect on the shape of the powerband.
Right now I'm looking pretty much dead set at 3.48 stroke and .30 or so over (.40 max)... I arrived at that because it had just the right mix.. It had more down low than the 3.25 stroke and more on top than the anything longer than 3.48...
The slightly longer LS series stock stroke should'nt be radically different.. I can't really see why getting all worked up and exotic with the bore and stroke should be on anyones list for a FI motor... It's all really about getting the intake, cams, head and exhaust just right...
The standard stroke just had the fattest power band... . If you are running alot of boost on a stroker there is bit more power down low and not as wide of a usable area where you really need it.
I have a hunch that on a supercharged motor with a pulley matching the longest posible strokes traits you could come up with a something that killed transmissions down low and fell flat soon after. If you build it like a "no replacement for displacement guy" then add alot of forced induction will be replacing hard parts sooner and if that does'nt happen wishing for a usable power band.. The ultra short stroke high rpm approach is has it's own weaknesses...
You know that snort you get between low and mid rpm with a NA 383 vs a 350... Well a properly matched turbo system on a 3.48 (350 stroke) engine makes that look like aboslutely nothing....
Honestly the 3.25 stroke was'nt too far behind down low due both engines being in the pre-mid spool but with the 3.48 the mid to upper rpm power band is a big fat plateau... That is a good thing.. I also thought it would lack the cruise, passable idle with a cam and drivability of the 3.48 stroke.
With the 3.48 stroke I experimented with bigger bores at this power level would require an expensive custom block to run reliably thick cylinder wall it only just flattened the powerband a bit more... It was big and fat enough already...
There is a steep HP climb as boost builds with all the bore stroke combinations that that is just turbo 101. Longer strokes reached boost quicker but not by enough to justify a steep drop off. The short stroke built boost later and had a weaker midrange and peaked late. With the 3.48 once boost builds and the right solid roller cam specs are used power climbs slowly from an already high spooled up power level to peak hp the in the mid 6k range and tapers slowly even beyond 8k rpm... There really is'nt a sharp peak on the graph but a broad arc...
2. Limit overbore to the minimum.. You need a thick wall to maintain cooling, block strength and a good ring seal.
The 383 would have wider powerband than the 447.
I honestly think you could make more power peak power on the shorter stroke... You will probably not be too far behind peak numbers with a 6.0 and have alot wider a power band.
For the turbo motor I'm working on I looked at a number of real world chevy turbo dynos and picked over the specs and results.. I also played with different engine combinations on desktop dynos... Just like the real thing they are only as good as the operator..
I ran looked at various strokes 3.0, 3.25, 3.48, 3.562, 3.75, 3.85 etc... I also looked at bores from 4.0 to a motown 4.2 or so....
I'd just run a minimal cleanup overbore and the stock stroke... You can't really get dramatic results from bore increases due to the limitations of the block and the fact that it just wont run as cool, be as strong or have as stable a ring seal...
It is less expensive and spending time and money on changing the displacement wont reap the same benefits as time and money on getting the cams, heads, intake and exhaust just right...
This is for a turbo LT1 yet the thinking carries over. Like I said alot still depends on the head and cams but every stroke and bore combination has its own effect on the shape of the powerband.
Right now I'm looking pretty much dead set at 3.48 stroke and .30 or so over (.40 max)... I arrived at that because it had just the right mix.. It had more down low than the 3.25 stroke and more on top than the anything longer than 3.48...
The slightly longer LS series stock stroke should'nt be radically different.. I can't really see why getting all worked up and exotic with the bore and stroke should be on anyones list for a FI motor... It's all really about getting the intake, cams, head and exhaust just right...
The standard stroke just had the fattest power band... . If you are running alot of boost on a stroker there is bit more power down low and not as wide of a usable area where you really need it.
I have a hunch that on a supercharged motor with a pulley matching the longest posible strokes traits you could come up with a something that killed transmissions down low and fell flat soon after. If you build it like a "no replacement for displacement guy" then add alot of forced induction will be replacing hard parts sooner and if that does'nt happen wishing for a usable power band.. The ultra short stroke high rpm approach is has it's own weaknesses...
You know that snort you get between low and mid rpm with a NA 383 vs a 350... Well a properly matched turbo system on a 3.48 (350 stroke) engine makes that look like aboslutely nothing....
Honestly the 3.25 stroke was'nt too far behind down low due both engines being in the pre-mid spool but with the 3.48 the mid to upper rpm power band is a big fat plateau... That is a good thing.. I also thought it would lack the cruise, passable idle with a cam and drivability of the 3.48 stroke.
With the 3.48 stroke I experimented with bigger bores at this power level would require an expensive custom block to run reliably thick cylinder wall it only just flattened the powerband a bit more... It was big and fat enough already...
There is a steep HP climb as boost builds with all the bore stroke combinations that that is just turbo 101. Longer strokes reached boost quicker but not by enough to justify a steep drop off. The short stroke built boost later and had a weaker midrange and peaked late. With the 3.48 once boost builds and the right solid roller cam specs are used power climbs slowly from an already high spooled up power level to peak hp the in the mid 6k range and tapers slowly even beyond 8k rpm... There really is'nt a sharp peak on the graph but a broad arc...
07-08-2004, 08:39 PM
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i know of a alum. 348 stock crank,forged pistons and rods long block for sale. 9:1 comp. low miles. smturley74@earthlink.net
07-08-2004, 09:18 PM
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I'll be looking for a 3.48 forged crank... Probably one of the better to best flavors... Otherwise snap...
That 334 will rev fast especially with a high end forged lightweight crank and it will put some good numbers.
That 334 will rev fast especially with a high end forged lightweight crank and it will put some good numbers.
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10-22-2014, 09:40 AM
#8
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If you want big cubes, you will need a aftermarket block. Unless you are doing 1/8th mile racing, where you need all of your toque early, then go with a stock stroke. A simple .030" over, 3.622" stroke iron block will be sufficient until you lift heads. How much power do you want? What are the goals for the car?
