compression ratio question
02-24-2008, 05:54 PM
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compression ratio question i have a stroker assembly that i am wanting to use but think it may be too much for pump gas.. the block hasn't been decked yet.. but its a 3.75 crank, 5.7 rods and kb704 pistons with stock lt4 heads? it says 9.7:1 with 76cc and 11:1 with 62cc but nothing for a 58-54cc.. i was think it would be like 11.7 or so.. i am planning on using a 1074 gasket if it can work.. want to use a cc306 or xfi 8-467-07
pistons
pistons
02-24-2008, 06:56 PM
#2
Your guess on compression looks close.
Honestly the only detail you listed that is a good ideas in that entire detail list are the 3.75 stroke and the head gasket is an OK choice, the rest NEEDS to be rethought.
Don't use KB pistons,
don't use LT4s especially not as cast
both cam choices are poor
I know that sounds harsh but would you rather have help doing it right now or help figuring out why it is slow later?
Honestly the only detail you listed that is a good ideas in that entire detail list are the 3.75 stroke and the head gasket is an OK choice, the rest NEEDS to be rethought.
Don't use KB pistons,
don't use LT4s especially not as cast
both cam choices are poor
I know that sounds harsh but would you rather have help doing it right now or help figuring out why it is slow later?
02-24-2008, 07:14 PM
#3
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Your guess on compression looks close.
Honestly the only detail you listed that is a good ideas in that entire detail list are the 3.75 stroke and the head gasket is an OK choice, the rest NEEDS to be rethought.
Don't use KB pistons,
don't use LT4s especially not as cast
both cam choices are poor
I know that sounds harsh but would you rather have help doing it right now or help figuring out why it is slow later?
Honestly the only detail you listed that is a good ideas in that entire detail list are the 3.75 stroke and the head gasket is an OK choice, the rest NEEDS to be rethought.
Don't use KB pistons,
don't use LT4s especially not as cast
both cam choices are poor
I know that sounds harsh but would you rather have help doing it right now or help figuring out why it is slow later?
02-24-2008, 07:20 PM
#5
I would not bother with as cast Trickflows either.
I would suggest trying to sell the LT4s, at least look into what you can sell them for, that might just make it possible to run good heads.
Ported LT1 castings are the right choice for the overwhelming majority of builds. The Trickflows are nice if you need a bigger chamber but that is about it.
I would suggest trying to sell the LT4s, at least look into what you can sell them for, that might just make it possible to run good heads.
Ported LT1 castings are the right choice for the overwhelming majority of builds. The Trickflows are nice if you need a bigger chamber but that is about it.
02-24-2008, 09:52 PM
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I would not bother with as cast Trickflows either.
I would suggest trying to sell the LT4s, at least look into what you can sell them for, that might just make it possible to run good heads.
Ported LT1 castings are the right choice for the overwhelming majority of builds. The Trickflows are nice if you need a bigger chamber but that is about it.
I would suggest trying to sell the LT4s, at least look into what you can sell them for, that might just make it possible to run good heads.
Ported LT1 castings are the right choice for the overwhelming majority of builds. The Trickflows are nice if you need a bigger chamber but that is about it.
as it sits with the xfi and lt4's as a 355 its not exactly what you would call slow. but i don't really have a track time or dyno numbers though but its the fastest the car has ever been..
02-25-2008, 03:00 PM
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SRP speed pro je weisco. get the compression height of the pistons, deck height of the block, compressed thickness of the gasket and the CC of your heads. along with any +/- dishing or relief of the pistons and i can figure up your CR
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02-25-2008, 03:20 PM
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Just my .02, I'm using the Speed Pro Forged Flat Top Pistons and with 64cc heads they say 10.76:1 compression and with 58 cc heads 11.55:1 compression. I'm going with the Lloyd Elliot LE2 H/C package and his heads are 56 cc. So I should get around 11.8:1 compression out of mine. I have already decked my block to zero and have plans on using a thinner Head Gasket, to raise my compression a little. Good Luck with your build. And BTW Capricemanager has alot of good points, I would listen to what he has to say. Although if money is an issue I would do what you feel comfortable with. But at least use forged pistons and port the stock heads or the LT4 Heads you already have.
James
James
02-25-2008, 05:04 PM
#9
Have the LT4's ported and rock on, in the right hands they flow300+cfm. Have the LT4 intake match ported.
The compression at 11.8 to 1 is fine, you need more camshaft for sure.
Will make good power, Ed Wright went 9.90's with LT4 heads and intake, cant be too awfully bad.
David
The compression at 11.8 to 1 is fine, you need more camshaft for sure.
Will make good power, Ed Wright went 9.90's with LT4 heads and intake, cant be too awfully bad.
David
02-25-2008, 05:24 PM
#10
Have the LT4's ported and rock on, in the right hands they flow300+cfm. Have the LT4 intake match ported.
The compression at 11.8 to 1 is fine, you need more camshaft for sure.
Will make good power, Ed Wright went 9.90's with LT4 heads and intake, cant be too awfully bad.
David
The compression at 11.8 to 1 is fine, you need more camshaft for sure.
Will make good power, Ed Wright went 9.90's with LT4 heads and intake, cant be too awfully bad.
David
I would not say the LT4s are outright bad but they are certainly not anywhere as good as they are assumed and reputed to be. Not when you look at RESULTS.
02-25-2008, 11:23 PM
#14
Alrighty then lol!
TAKE YOUR CRANK THROW DIVIDE IT BY 2 = 1.875
ADD THAT TO YOU ROD HEIGHT 1.875 + 5.7 = 7.575
ADD THAT TO YOUR PISTONS COMPRESSION HEIGHT (unknown)
Subtract that from your PTD clearance 9.025-7.575= 1.45
1.45 is the amount you have to play with until you know the compression height of the piston. Say the compression height is 1.250 then you would subtract that from 1.45 to get .20 PTD. That would make the .029 gasket the right choice placing your quench at .049!
Buy a head gasket to suit the quench! For optimum results you want to be at least .039 and no more than .050.
I would also recommend staying away from the KB pistons and utilizing a flat top piston with a stock Combustion chamber. Also look for a piston that keeps the pin height out of the ring lands. Just .02
TAKE YOUR CRANK THROW DIVIDE IT BY 2 = 1.875
ADD THAT TO YOU ROD HEIGHT 1.875 + 5.7 = 7.575
ADD THAT TO YOUR PISTONS COMPRESSION HEIGHT (unknown)
Subtract that from your PTD clearance 9.025-7.575= 1.45
1.45 is the amount you have to play with until you know the compression height of the piston. Say the compression height is 1.250 then you would subtract that from 1.45 to get .20 PTD. That would make the .029 gasket the right choice placing your quench at .049!
Buy a head gasket to suit the quench! For optimum results you want to be at least .039 and no more than .050.
I would also recommend staying away from the KB pistons and utilizing a flat top piston with a stock Combustion chamber. Also look for a piston that keeps the pin height out of the ring lands. Just .02
02-26-2008, 05:55 PM
#16
The results are not in line with what folks assume they are.
AI will port LT4s and still I would suggest folks sell them and get LT1 heads to port instead. Come out pretty good money wise that way as someone will be willing to pay good money for LT4s again assumning they are somehow great.
Guys are getting 480-530rwhp NA through automatics with aggressive setups and the AI 200cc LT1 casting. It is a joke that every kid who dreams of running 11s thinks they need LT4 or aftermarket castings.
AI will port LT4s and still I would suggest folks sell them and get LT1 heads to port instead. Come out pretty good money wise that way as someone will be willing to pay good money for LT4s again assumning they are somehow great.
Guys are getting 480-530rwhp NA through automatics with aggressive setups and the AI 200cc LT1 casting. It is a joke that every kid who dreams of running 11s thinks they need LT4 or aftermarket castings.
02-26-2008, 05:59 PM
#18
why would you sell LT4 heads to buy stock LT1s? That makes no sense at all. but since you only believe what AI says...
That's funny, even AI says the LT4s are "GM's best reverse cooled casting". That is straight from their site.
They also say the LT4 heads have "the capacity to generate 20-30hp over our proven 200cc CNC'd GM LT1 offering".
Those sound like some really shitty heads to me.
The only problem with the LT4s is people thinking they can do the "LT4 conversion" and switch from as cast LT1s to as cast LT4s and think they will gain anything. If you are talking about porting them, they are at least as good or better than the LT1s.
In summary: Even AI says the LT4s are better. lol
They also say the LT4 heads have "the capacity to generate 20-30hp over our proven 200cc CNC'd GM LT1 offering".
Those sound like some really shitty heads to me.
The only problem with the LT4s is people thinking they can do the "LT4 conversion" and switch from as cast LT1s to as cast LT4s and think they will gain anything. If you are talking about porting them, they are at least as good or better than the LT1s.
In summary: Even AI says the LT4s are better. lol
Last edited by infinitebird; 02-26-2008 at 06:35 PM.
03-01-2008, 02:45 PM
#19
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holy crap.. i asked a compression ratio question.. and i talked to AI and they had no problem with porting the lt4 nor did they try and talk me into selling my heads for lt1's.. jesus christ.. i have a set of lt1 heads also that i could have sent to be ported. or i could get the trick flows.. either way you need to take a ******* pill with supporting AI. they make a great product. big ******* deal. are you that worried about justifying your engine that everyone has to build your motor. I would love to buy a set of AI ported heads.. but redoing my whole damn engine and getting AI heads may not be in my budget at the moment so if i have a set of ******* lt4 heads which in this case would make more power then the set of lt1 heads i also currently own, wouldn't they be better suited on a bigger engine? wouldn't you think so? and if i can get away with not having to pay out the *** and get new trick flows that aren't ported because of a potential compression ratio issue, then maybe down the road i could save some cash and get my lt1 heads ported by AI .. can you sleep at night now?
03-01-2008, 03:25 PM
#20
why would you sell LT4 heads to buy stock LT1s? That makes no sense at all. but since you only believe what AI says...
That's funny, even AI says the LT4s are "GM's best reverse cooled casting". That is straight from their site.
They also say the LT4 heads have "the capacity to generate 20-30hp over our proven 200cc CNC'd GM LT1 offering".
In summary: Even AI says the LT4s are better. lol
That's funny, even AI says the LT4s are "GM's best reverse cooled casting". That is straight from their site.
They also say the LT4 heads have "the capacity to generate 20-30hp over our proven 200cc CNC'd GM LT1 offering".
In summary: Even AI says the LT4s are better. lol
Maybe he has some customers with the LT4s running hard that I am not aware of
, I just do not see any LT4 headed cars that really impress me when compared to some of the LT1 stuff being put out these days. 
