Hey, Im trying to find ways to bump up the Compression on my 489, and Im wondering what the minimum safe quench distance for a long stroke high rpm motor is.

Right now im at a .040 gasket. I had the engine zero decked, but to my eye (albeit untrained) It looks like the pistons are still down in the bore slightly.

Also, Ive already had the 990 heads decked .020, is there anymore left in them? I have SRP mild domes rated at 10.25:1... Im trying to reach 10.75 to 11:1 compression.

Thanks! graemlins/beers.gif
Jason

I'm not an expert, but on my 489, I'm using the SRP 18cc dome pistons. When I ordered my AFR heads, I had them milled to 115 cc (.036) and with the recomended felpro gasket, I'm still only about 10.4:1. This is a true zero deck motor too. I used Pats calculator for the these figures. What is the cc on a 990 head chamber? I cant see getting the compression that high with that piston. Maybe wolfplace will chime in. :D
Steve

990 started at 118, had them milled .020 for 115 roughly.

Using pats calculator, Im at roughly the same place you are :cool:

My 496 came out at 0 to +.005 deck. I'm also using the SRP 18cc pistons. We didn't deck it that way, but with a previous deck job, line bore and the new crank and rods, this is where we ended up. Not all holes will be the same due to tolerance stack ups.
Anyway, my guy got real queasy about using an 041 gasket. He feels that with the stroker crank, the crankpin overlap isn't enough to keep the crank from flexing at high rpm and the pistons could end up hitting the head.
So we went the other way and are using the .051 gasket. This dropped me down to around 9.4:1.
I'll be curious to what the machine shop guys here say about the required clearance.
Ron

Don't know if this will help you but I run a true zero deck and .039 compressed gasket on my 461 and spin it to 6500rpm regularly and on inspection saw no signs of contact.

You are not going to have a problem at .039 with steel rods & a reasonable piston to bore clearance but you need to check them all as you don't want one to be a "surprise" ;)

I ran a 482 years ago before I "knew better" :D that I shifted at 8000+ & went through the lights at about 8200-8500 depending on gear with the pistons .005-.006 out with a .039 gasket & they were just showing signs of hitting on the quench side.
Ran it that way for 2 or 3 years & sold it to a boat guy after that. damn thing had so much time on it it was getting a ridge LOL

Not recommending you run it this close but it can be done especially under 7000 or so.

If you have the heads off the engine (jusdging by your comment about the pistons being in the hole some) then you should spend some time studying the combustion area around the piston. See what sort of signs the engine is providing you. Less isn't always better. If you go too tight on the quench with a domed piston you may reduce the effective combustion area. If the area around the valves that roughly approximates the chamber area is carboned up then you may be good already. Look for clean areas on the non-flat piston surfaces. This is a sign that you might be tight on quench already. I'm at .051 quench with a 32cc piston and I could probably increase the quench area just a tad by milling the intake relief or rolling the head. HTH.

Originally posted by kjett:
If you have the heads off the engine (jusdging by your comment about the pistons being in the hole some) then you should spend some time studying the combustion area around the piston. See what sort of signs the engine is providing you. Less isn't always better. If you go too tight on the quench with a domed piston you may reduce the effective combustion area. If the area around the valves that roughly approximates the chamber area is carboned up then you may be good already. Look for clean areas on the non-flat piston surfaces. This is a sign that you might be tight on quench already. I'm at .051 quench with a 32cc piston and I could probably increase the quench area just a tad by milling the intake relief or rolling the head. HTH. Ken,
I am missing something here??
I totally agree with you about the flame travel around the dome & chamber area but you completely lost me regarding the valve notch & quench?

The quench is only the flat part of the head & piston & does not involve the chamber area at TDC unless you lower the piston enough (or full dish it) that it becomes part of the chamber.

My experience has been that the tighter you keep the quench the less prone an engine is to detonation & the more efficient it seems to become

Originally posted by Wolfplace:
</font><blockquote>quote:</font><hr />Originally posted by kjett:
If you have the heads off the engine (jusdging by your comment about the pistons being in the hole some) then you should spend some time studying the combustion area around the piston. See what sort of signs the engine is providing you. Less isn't always better. If you go too tight on the quench with a domed piston you may reduce the effective combustion area. If the area around the valves that roughly approximates the chamber area is carboned up then you may be good already. Look for clean areas on the non-flat piston surfaces. This is a sign that you might be tight on quench already. I'm at .051 quench with a 32cc piston and I could probably increase the quench area just a tad by milling the intake relief or rolling the head. HTH. Ken,
I am missing something here??
I totally agree with you about the flame travel around the dome & chamber area but you completely lost me regarding the valve notch & quench?

The quench is only the flat part of the head & piston & does not involve the chamber area at TDC unless you lower the piston enough (or full dish it) that it becomes part of the chamber.

My experience has been that the tighter you keep the quench the less prone an engine is to detonation & the more efficient it seems to become </font>[/QUOTE]Mike,

That's what happens when I stay up late typing on the computer after having been on it all day long :D What I meant to say is that I could increase the quench, round off the valve relief or roll the head. I've got a small dead spot on all my pistons at the edge of the valve relief and the dome rise where fuel is washing. It's because the quench is too tight for that chamber/dome match at .051! All I'm suggesting is to LOOK at what the engine is telling you. IMO I think it's misinformed to just rush off and make changes to an engine on paper (8.2 dcr, .040 quench, blah blah blah) when you have the information in front of you to examine and act on. But then again, what do I know smile.gif

I'd probably go with one of the second two & leave the quench tight,,,, also, you might be interested in some Mondello's work with wet flow.
It seems some of the ideas on fuel wash are changing dramatically with regard to clean spots on pistons. ;)

Now go to bed :D

===========edit============
All I'm suggesting is to LOOK at what the engine is telling you. IMO I think it's misinformed to just rush off and make changes to an engine on paper (8.2 dcr, .040 quench, blah blah blah) when you have the information in front of you to examine and act on. But then again, what do I know

you type to fast,,,,
Completly agree with your last edit graemlins/thumbsup.gif

How about I show you?
A picture is worth a thousand words...
And I know its dirty, I had a head gasket problem, not to mention running realllllly rich, oh and I cleaned up one of the pistons tongue.gif

http://www.we-todd-did-racing.com/wetoddimage.wtdr/wNjYwNDQ3NnM0MTNkZmQzMXk1NDE%3D.jpg
http://www.we-todd-did-racing.com/wetoddimage.wtdr/wNjYwNDQ4NnM0MTNkZmQzMXk1NDE%3D.jpg