Better or worse?tighter quench.

Im trying to build my first motor based on a friend of mines.It will be 10.8-1 compression with iron heads.Anyway I was wondering if swapping my 0.039 head gasket to a 0.020 one would help with detonation or make it worse because it would increase my compression to 11.4-1.My quench would be better with the thinner gasket at 0.045 as apposed to 0.064 with the thicker.Just wondering what you guys thought thanks.


Register now (free) or login to remove ads

Is your build too far along to sub a piston w/a shallow (say, 8cc or so) D-shaped dish over the chamber?

A lot depends on the combo and use. Can you fill us in on that?

Well I dont really want to buy pistons cause i already spent $400.00 on dome pistons and got them pressed on my rods.They have a small 3.5 cc dome and my heads are 041 64cc 1970's.Im building it for high performance street only.Its a 350 chevy bored 30 over,4 bolt mains.

You're into the grey zone there, but I think it would be too much unless you are willing to mix in race gas

My friend does it on 91 octane at 11-1 compression with camel hump heads but he has to knock his timing back.I really dont want to have to mix my gas.

Open up the chambers on the head to 69cc. This would help in three ways-- Allow you to close up the quench clearance, keep the comp ratio from being too high, and unshroud the valves for more flow.

Eric has the right answer. Open the chambers by unshrouding the valves
to lower the compression, then install the thinner head gasket to set
the squish clearance.

If the dome is solid, consider removing portions of the dome to lower the
compression further, target ~10.2:1 compression.

I don't really want to get into opening up the chambers because it would take away from the resale value of my heads if i switch to aluminum down the road.I also think my domes are hollow.But I thank you for your advice guys.

What is the brand and part # of your pistons?

Heads are stock, no porting at all?

Why did you copy your friends combo knowing that his won't run on your local pump gas without retarding the timing?
If he and the rest of us are limited by the laws of physics, what makes you think you are going to get a different or better result?

If we could actually do this with the pump fuel you got, with a SBC motor, why would the gas companies bother making hi octane gas for high compression ratio motors?

Pistons (the right piston for your motor) are cheap. Why not change the pistons? Its a lot easier and cheaper to do it now than later when the ring lands bust from engine knock.
Even the cheapest $80 flat top cast 350 piston will outlast a more expensive piston when the wrong piston (your domed pistons) is used while the engine is knocking.
If you are worried about reducing the potential resale value of your 041 heads,
Why not sell them now for some better flowing heads with larger chambers?

You have lots of workable solutions. Changing the pistons is the cheapest, and quickest and best cure. Anything worth doing is worth doing right.
http://store.summitracing.com/partd...30&autoview=sku
This is a great street/strip high performance hyper design piston. Its all the piston you need.
Sell your $400 piston mistake to some one else.
For every one building a 350 with flat tops and 64cc heads there is another using 70-76cc heads or wants 12:cr to go racing that needs your pistons.

With a flat top piston in your motor you'll get the right compression ratio and quench using a .015" to .026" head gasket. These are commonly available.
Build your motor correctly with correct workable compression ratio and set your timing for max performance (34 to 36deg) and go show your buddy how its done.

You need to throw a set of gears and a high stall in that car, with that 350 combo. (4.10-4.56)

Posted by F-BIRD'88......
"Why did you copy your friends combo knowing that his won't run on your local pump gas without retarding the timing?
If he and the rest of us are limited by the laws of physics, what makes you think you are going to get a different or better result?"

Beautiful, just friggin' beautiful.

A 355 with 64cc heads, 0.025" piston deck height, 3.5cc dome pistons and a Victor Reinz 5746 head gasket that compresses to 0.025" will put your squish at 0.050" and your static compression ratio at 11.14:1. Screw the motor together and bolt on some water injection.....
http://cgi.ebay.com/ebaymotors/Snow...sQ5fAccessories
http://cgi.ebay.com/ebaymotors/Cool...sQ5fAccessories
http://cgi.ebay.com/ebaymotors/NOS-...sQ5fAccessories

Do a search for water injection. There are a ton of units out there.....some good, some not so good....Heck, when you get the motor together and want a stopgap system until you can do better, get a windshield washer bag and pump off a Ford at the boneyard. Route a line into the top of the carb right in the middle so that it will spray down both barrels of your 4-bbl and use a tip that is drilled to 0.030". I have used an old blank carb jet before. Set the pump up with a microswitch that runs off the primary throttle blades and activates at around 1/4-1/2 throttle. Go to the drug store and get some isopropyl alcohol. Mix it 2 parts of alcohol to 3 parts of distilled water.

One 0.030" hole is 0.0007068 square inches. If you want to run two hoses, one to each throttle bore at the carb, then drill your tips 0.021". Two at 0.021" is 0.0006927 square inches.

Thanks you guys , I think I will switch to flat tops, better to be safe then sorry the water injection is a cool idea but i think its a little more complex then just swapping pistons.Thanks again.

powerhunter,here is a link to car shows & drag race schedule at Greenfield,if you're interested.Digby Scallop Days arent on there,but that car show will be around Aug 7.
Guy
http://www.maritimeclassiccars.com/disp_events_list.php

Was curious as to what piston you had because if it is the TRW/Speed-pro Forged copy of the original LT-1 piston, then the dome can be machined to a flat top. Check your dome, if it is solid, just machine it. It ain't brain surgery!

I'm a little disappointed, some of the sharpest guys on here replying and I haven't seen DCR mentioned once. What cam are you running? That's going to have a big influence on what octane you can get buy with.

Check this out........

DCR Combinations that worked.




Check it carefully. The current Speed Pro "TRW" pistons aren't exact copies of the old TRW's. They may have the same part numbers and dome or dish configurations on top but that's where it ends. I compared a new L-2441 D-Cup to my old TRW L-2441's, they have the same D-Cup volume but that's where the similarity ends. The current ones are a different weight, pin height is .020" closer to the top which means the new ones will be that much farther down the bore and the internal structure is different.