LT1 Build up need some help
Thread Starter
Pro
Joined: Oct 2004
Posts: 653
Likes: 10
From: Walton Kentucky
LT1 Build up need some help
I am building an Lt1 with :
10:3 SRP Piston
LT4 Extreme Duty timing chain
LT4 Hot Cam Kit
LT1 heads with 2.00 intake and 1.55 Exhaust with port matched intake and some bowl cleanup
28lbs Bosch injectors
impala head gasket
Now my question, with the pistons and the Impala gaskets will my compression ratio be too high for premium gas?
10:3 SRP Piston
LT4 Extreme Duty timing chain
LT4 Hot Cam Kit
LT1 heads with 2.00 intake and 1.55 Exhaust with port matched intake and some bowl cleanup
28lbs Bosch injectors
impala head gasket
Now my question, with the pistons and the Impala gaskets will my compression ratio be too high for premium gas?
Racer
Joined: Apr 2003
Posts: 342
Likes: 0
From: Kalamazoo MI
Just curious but what brand head gasket are you using? I'm about to bolt on my shiny new Stage 3 LT4's from Precision Porting and am between the Felpro teflon coated or something from Cometic. I too was planning on using a thinner gasket. My understanding is it doesn't bumb compression significantly, maybe from 10.5 to 10.8, but it does improve quench height in the combustion chamber and thus the efficiency of the burn.
Safety Car
Joined: Dec 2002
Posts: 3,655
Likes: 24
From: Charleston SC
What dish is the psiton? did SRP say it would be 10.3:1 withthe LT1 heads? If so you are fine I think the stock CR is 10.7:1 and i have seen many LT1s in the 11.5-12.5 range with no problems.
Drifting
Joined: Mar 2005
Posts: 1,923
Likes: 0
From: GA
Originally Posted by tvetta
I really don't know very much about engines and was throwing the questions out there.
What does that do for me the LT1 are 50-55cc vs 64cc?
What does that do for me the LT1 are 50-55cc vs 64cc?
Switch to a gasket with a .060" compressed thickness and your compression will drop to 11.58:1, a little more manageable on preimum gas.
Worst case with a 50cc head and .040" gasket you are looking at 13.29:1 CR (better run race gas)
50cc head and .060" gasket is 12.42:1
Last edited by Morley; Jun 14, 2005 at 06:45 PM.
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Safety Car
Joined: Dec 2002
Posts: 3,655
Likes: 24
From: Charleston SC
Using the static CRs that Morley gave and knowing you are going with a fairly mild cam i would try to stay below 12:1 if possible. If you had chose a more agresive cam you could go a little higher but as long as you end up below 12:1 withg the hot cam your dynamic should be fine. If it where me I would use the .060 head gasket and scrap the impalla gaskets for another project with your set up.
Le Mans Master
Joined: Jan 2003
Posts: 8,596
Likes: 19
From: Portland Oregon
Originally Posted by tvetta
I am building an Lt1 with :
10:3 SRP Piston
LT4 Extreme Duty timing chain
LT4 Hot Cam Kit
LT1 heads with 2.00 intake and 1.55 Exhaust with port matched intake and some bowl cleanup
28lbs Bosch injectors
impala head gasket
Now my question, with the pistons and the Impala gaskets will my compression ratio be too high for premium gas?
10:3 SRP Piston
LT4 Extreme Duty timing chain
LT4 Hot Cam Kit
LT1 heads with 2.00 intake and 1.55 Exhaust with port matched intake and some bowl cleanup
28lbs Bosch injectors
impala head gasket
Now my question, with the pistons and the Impala gaskets will my compression ratio be too high for premium gas?
First of all what displacement are you going to run? If its a 383, then a flat top with -5cc for valve releifs with stock 55cc chambers, and a .039 compressed gasket thickness would give you around 12.5 to 12.7:1 compression.
If you are talking about a stock 350 displacement + a .030 overbore for the new pistons then using a stock head, figure zero deck meaning that the pistons are even with the top of the block deck. With that combo, a 55cc head, .039 head gasket you should end up with around 10.5 to 10.8:1 CR. Stock LT4's were running around 10.5:1 using a 54cc head and a .041 gasket. Their pistons were slightly taller in dome height but they were still effectively a flat top with eye brows. Assuming the new SRP pistons have valve releifs they are typically -5cc in volume.
LTx engines with their efficient reverse cooling are good to 11:1 on pump gas. I am presently in the process of building a 383 with a -11cc dished piston and 55cc heads to give me a final compression of 11:1, this is also calculated with the pistons in the "hole" .005 to allow for piston rock as these will be the 2618 alloy pistons which require a little more clearance.
Safety Car
Joined: Dec 2002
Posts: 3,655
Likes: 24
From: Charleston SC
Tom I come up with a bit diferent CR for the -5cc dish FT (Finaly looked up the PN) did I screw somthing up? It does corilate withthe SRP web sites
Again confirm this with SRP but I would stick withthe stock .060 gaskets and sell the Impalla ones
Cylinder head Volume (CC) = 55.00
Piston Top Volume (CC) = -5.00
Cylinder Bore (Inches) = 4.030
Cylinder Stroke (Inches) = 3.48
Deck Height (Inches) = 0.030
Head Gasket Thickness (Inches) = 0.040
Computation Results:
Computed Compression Ratio is 12.3 to 1
Input Parameters Are the Following:
Cylinder head Volume (CC) = 55.00
Piston Top Volume (CC) = -5.00
Cylinder Bore (Inches) = 4.030
Cylinder Stroke (Inches) = 3.48
Deck Height (Inches) = 0.030
Head Gasket Thickness (Inches) = 0.060
Computation Results:
Computed Compression Ratio is 11.6 to 1
SRP web site states 11.1 with 58 cc heads 3.48 strole and 4.030 bore
http://www.jepistons.com/pdf/2005-srp.pdf#search='SRP%20pistons%20compress ion%20ratio'
My calculator comes up with
Input Parameters Are the Following:
Cylinder head Volume (CC) = 58.00
Piston Top Volume (CC) = -5.00
Cylinder Bore (Inches) = 4.030
Cylinder Stroke (Inches) = 3.48
Deck Height (Inches) = 0.030
Head Gasket Thickness (Inches) = 0.060
Computation Results:
Computed Compression Ratio is 11.1 to 1
Again confirm this with SRP but I would stick withthe stock .060 gaskets and sell the Impalla ones
Cylinder head Volume (CC) = 55.00
Piston Top Volume (CC) = -5.00
Cylinder Bore (Inches) = 4.030
Cylinder Stroke (Inches) = 3.48
Deck Height (Inches) = 0.030
Head Gasket Thickness (Inches) = 0.040
Computation Results:
Computed Compression Ratio is 12.3 to 1
Input Parameters Are the Following:
Cylinder head Volume (CC) = 55.00
Piston Top Volume (CC) = -5.00
Cylinder Bore (Inches) = 4.030
Cylinder Stroke (Inches) = 3.48
Deck Height (Inches) = 0.030
Head Gasket Thickness (Inches) = 0.060
Computation Results:
Computed Compression Ratio is 11.6 to 1
SRP web site states 11.1 with 58 cc heads 3.48 strole and 4.030 bore
http://www.jepistons.com/pdf/2005-srp.pdf#search='SRP%20pistons%20compress ion%20ratio'
My calculator comes up with
Input Parameters Are the Following:
Cylinder head Volume (CC) = 58.00
Piston Top Volume (CC) = -5.00
Cylinder Bore (Inches) = 4.030
Cylinder Stroke (Inches) = 3.48
Deck Height (Inches) = 0.030
Head Gasket Thickness (Inches) = 0.060
Computation Results:
Computed Compression Ratio is 11.1 to 1
Last edited by FD2BLK; Jun 14, 2005 at 09:47 PM.
Large Impressive Member
Joined: Jul 2003
Posts: 65,811
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From: Good health is merely the slowest possible rate at which one can die
St. Jude Donor '04-'05-'06-'07
Originally Posted by tvetta
I am using the GM gaskets.
The pistons are SRP 138081 and the compression ratio is calculated using zero deck clearance with .040 gasket and 64cc heads on a small block
The pistons are SRP 138081 and the compression ratio is calculated using zero deck clearance with .040 gasket and 64cc heads on a small block
Thread Starter
Pro
Joined: Oct 2004
Posts: 653
Likes: 10
From: Walton Kentucky
Guys, I can't begin to thank all of you for your help!
I spoke to my Machine Shop and he said that was an overlook on his part. Everything is cool, going with the stock replacement compression piston.
Regards,
Tony
I spoke to my Machine Shop and he said that was an overlook on his part. Everything is cool, going with the stock replacement compression piston.
Regards,
Tony
Le Mans Master
Joined: Jan 2002
Posts: 5,556
Likes: 0
From: Jenison MI
Cruise-In VI Veteran
Cruise-In VII Veteran
St. Jude Donor '06
Originally Posted by tvetta
I am glad I started this thread.
Me too.... I just learned something.. Now I need to find the calculator to figure tis stuff out on myown
