Red97GT

I'm getting a TSP 347 short block after my stock LS1 broke a rod with 65k miles on it.

I'm using the stock heads unmilled and a Brian Tooley stage 3 cam with his springs and push rods.

The TSP comes with a weisco -3.2 cc piston that will drop the compression down over the stock 10.1
So it was mentioned to use a cometic 0.40 head gasket to make up for the loss of compresion.

Will a 0.40 head gasket change the pushrod length from the stock 7.40

is it worth using a cometic 0.40 to regain the comression or is it better to go back to GM MLS gasket???

How mush compresion will it drop with a -3.2 piston???

Thanks in advanced

handyandy496

iTrader: (9)

Ya run the .040 it will give u better quench as well.

Red97GT

but what about push rod length??

handyandy496

iTrader: (9)

Its only .011 diff. Nothing to worry about. Are your pistons @ deck or out of the hole?

Dino1

Push rod length checker, and proper pattern will need to be checked.

Manton and Smith can make you any length you need.

This is very critical for proper geometry, and can make or break you.

Valve guide wear and lash setting will be effected if you don't do it right.

handyandy496

iTrader: (9)

My pistons are just below deck so im running a .036 gasket. That would get you all your compression back but if there above deck.. .040 is great.

Dino1

Times the rocker ratio, the whole setup will be off, and the rocker trunyon will not ride with proper pattern through the rocker stroke on the valve tip. It will move outward of center.

Valve train geometry is more critical than most give insight to. Especially in high RPM usage.

Red97GT

I dont know what deck is. I dont have the short block yet. I would have to call TSP to find out.

Red97GT

I agreee pushrod length could cause problem. So it it worth getting compersion back with a 0.40?? how much comression will be lost with a wiesco -3.2??

99Bluz28

iTrader: (35)

You'll lose about .36 point with the 3.2 cc dish. With the .40 gaskets it'll bring the SCR up about .24, so you'll still be down about .12 point. IMO get the stock heads milled down enough to as least get it back to stock SCR or slightly higher. You will have slightly more PR preload so you will most likely need new shorter PRs.

Red97GT

milling head may still happen, wont know until heads come off and get inspected. may have to send them out for 3 angle. they only have 65k on them. new Brian tooley spring are going to be installed and the cam kit i can choose PR length. I just was hoping to get length right the first time.

JimMueller

iTrader: (9)

TSP also offers a Diamond -2cc 3.905 bore flat top piston (appears to be PN 11502) which is advertised as having a -.010 positive deck, for an extra $100.

The Wiseco -3.2cc 3.903 bore piston is advertised as having a compression height of 1.304, which would indicate it is flush with the deck.

The head gasket should be the same size (or next size larger) than the cylinder bore or the chamber (whichever is larger). Realize that for a Cometic to seal properly there is a specific surface finish that is required on the block and heads, and they may leak if it's not prepped correctly. If you're willing to surface the deck & heads correctly, then I say go with the Cometics.

If you don't want to worry about the surfacing, then you'll need to go with something like GM graphite or MLS gaskets, but they are thicker and will drop your compression even further. Using the Diamond -2cc 3.905 pistons would help offset that compression loss.

stock LS1 heads unmilled chamber 66.67cc
Cometic gasket thickness & bore .040 & 3.910
Bore 3.903
Stroke 3.622
deck clearance - 0 for Wiseco
Compression: 10.135:1
Compression with GM graphite gasket (.054 compressed, 3.91"): 9.822

Using the Diamond piston with same Cometic gaskets, static compression is 10.5. Using the Diamond pistons with the graphite gasket, compression is 10.19.

If you don't want to use Cometics, then I say pick the Diamond pistons and mill the heads to get a 63-64cc chamber to get back to 10.5:1 compression.

If you want to use the Cometics, and want to save the money on the pistons by getting the Wiseco's, I still suggest milling the stock heads to ~63-64cc to get back to 10.5 compression.

As others have already commented, you should always measure pushrod length manually during assembly. In theory, any overall shortening of the stack of components between the cam lobe and the rocker arm will require a shorter pushrod. The Cometic gasket would be ~.011 thinner, and if you milled the heads to 63-64cc chambers that'd reduce it another ~.035. So if you did both in theory you'd need a pushrod ~.046 shorter than stock. If you're going to be buying new pushrods, consider buying the largest diameter, thickest wall pushrod you can afford which clears the guide holes. If the heads are already off, perhaps they can perform minor clearancing to help with that.

Red97GT

[QUOTE=JimMueller;

The Wiseco -3.2cc 3.903 bore piston is advertised as having a compression height of 1.304, which would indicate it is flush with the deck.



If you don't want to worry about the surfacing, then you'll need to go with something like GM graphite or MLS gaskets, but they are thicker and will drop your compression even further. Using the Diamond -2cc 3.905 pistons would help offset that compression loss.

stock LS1 heads unmilled chamber 66.67cc
Cometic gasket thickness & bore .040 & 3.910
Bore 3.903
Stroke 3.622
deck clearance - 0 for Wiseco
Compression: 10.135:1
Compression with GM graphite gasket (.054 compressed, 3.91"): 9.822



As others have already commented, you should always measure pushrod length manually during assembly. In theory, any overall shortening of the stack of components between the cam lobe and the rocker arm will require a shorter pushrod. The Cometic gasket would be ~.011 thinner, and if you milled the heads to 63-64cc chambers that'd reduce it another ~.035. So if you did both in theory you'd need a pushrod ~.046 shorter than stock. If you're going to be buying new pushrods, consider buying the largest diameter, thickest wall pushrod you can afford[/QUOTE]

Thanks Jim great info. So i think i want to use a MLS since heads are being reused. I know i will be leaving some horsepower on the table since compresion is going to be down slightly.

I am getting .80 PR from BTR comes with there cam and spring cam kit. in therory i can use a 7.40 PR

Russ K

iTrader: (1)

Push rod length doesn't affect rocker arm geometry on an LS engine.

Russ Kemp

maroonls1z

I was curious about that too? Wouldn't preload just be increased using factory length rods? Unless it bottoms out the lifter when running I wouldn't thing it would effect oem rocker scrub pattern

JakeFusion

iTrader: (7)

Mill the heads. You now have at least .160" of additional clearance on the intake side with the reliefs and something like .120" on the exhaust. Mill them down to 62-63cc and let her rip with the Cometics (.036" if zero deck and .045" if out of the hole .010") because you want quench around .035".

You'll need to measure pushrod length after doing that depending on what lifters you run.