vette427-sbc

Is there a rule of thumb for ideal quench #'s when building a boosted motor? Currently have a .045 quench (.020 gasket, .025 deck) and ~10.4 compression. If I get a thicker gasket I can get to a reasonable compression ratio (~9.5) but the quench obviously goes out the window. Not looking to build a crazy motor (yet), but would like to put 8ish PSI through it without changing too much.
Dart SHP 406 with AFR 195's

dochorsepower

BE CAREFUL. Don't negate the beautiful combustion chamber design of those AFR's with a thick gasket. 9.5 compression and 8 psi, you're going to be buying a lot of pistons.

7t9l82

why not leave it alone and use less boost, there are guys doing that.

vette427-sbc

Why do you say that? There are plenty of people running way more than 8psi on 9.5 compression. The plan is to run an intercooled D1SC.
The motor has mahle forged flat top pistons and I would prefer to not have to tear into the bottom end for now unless dished pistons are a necessity.

Im not going to spend $5k on a blower setup and run 5-6psi to make ~75 more hp.

What I want to do is see if I can make the most of the parts that I have. If it is not bad practice to use a thicker gasket to lose some compression for the sake of boost then I will do that until I feel like tearing into the bottom end to build a motor that will take more boost.

Solid LT1

I would rework combustion chambers for more volume rather than run a gasket that is too thick.....more than 0.050" and your losing efficiency.

HBZ_81_C3

We run .080 quench on a 540 BBC twin turbo set up. However, we run 7 times the boost level you are looking to run.

Be very careful on timing with it. The Mahle pistons, depending on the design may not like boost. The Mahle's I have seen, which isn't many, were built very light with thin ring packs and not a lot of material above the top ring. This type of piston design typically is not friendly in any power adder application.

Double check what the piston design is to make sure of exactly what you have. If they are as I described, I would be very careful in my decision to boost it. If it is not happy with the boost and timing it will let you know real quick with the top pulled off of pistons or top ring lands lifted.

C3's and power adders are a lot of fun!

Be careful and have fun!

dochorsepower

One thing to remember is that a lot of guys running a lot of boost (like in C-5, C-6 Vettes) also have electronic spark control that senses the onset of detonation and adjusts the spark advance and/or mixture to protect the engine. If you are going to boost a C-3, you need to incorporate this kind of system OR get a good supply of replacement pistons and rings.

Gale Banks 80'

On my first Motor I went with 7.8 to 1 with twin Turbocharging. What was considered a standard at the time. The motor was a real dog off idle, couldn't get out of its own way till it made some boost. My current Motor is right at 10 to 1 and makes decent HP prior to boost. No Intercooling. Having a Computer run the show is the real trick to success. If You look at the Factory ZR-1 LS9 You will also see the general kept Compression in it.

bluedawg

what size chambers do your afr's have? You might be able to go to a 210 which has better intake & exhaust flow and run 76cc chambers if your not already.

bashcraft

You're running 56 lbs. of boost on a gasoline engine?

cardo0

I have never come across a rule of thumb for quench in boosted motors. I have read that in high rpm motors too tight quench can be unproductive. Also, with static compression less than 9:1 quench has little effect.


Generally for a street/strip motor u want quench height greater than .035" but by 0.060" it has little effect on combustion.

I would be more worried 'bout quench area and maximize my chamber volume for the supercharger. Like i would want my unswept volume to be in the head chamber as much as possible rather than in a piston dish. If u want to know more u could google it as my explanation my not be the best.

Like Solid LT1 said reworking the chambers to open them up to increase unswept volume and nail your static volume is the best idea. Getting the chambers polished out and volume matched should not be very expensive as the chamber areas are easier to access and work on (compared to the head runners). That way u could add a lot more boost too.

Good luck and let us know how it works out for u.