03 BUSA

iTrader: (25)

OK guys, I finally have hard numbers to play with. What are your opinions?
.005 out of hole
257.2 @ 50
266 @ 50
iopen 18.6 btdc
iclose 58.6 abdc
eopen 63
ex close 23
110 lsa
110 icl
.056 compressed gasket (GM)

I come up with a DCR of 8.4.1 and SCR of 11.3.1 Quench is not great at .051
However, Cometic has nothing but a .051 compressed gasket and for $100 more I did not feel it was worth it. If i went with the Cometic .051 I come up with 11.4 SCR and 8.491 DCR and a Quench of .046. This is on a 427ci NA motor. Let me hear what you guys think. I was told by the builder to just leave at 8.4 with factory gaskets as HP would only be a minimal loss (5-7) and it would be a safer bet on pump gas with no issues of detonation in extreme heat. Thanks for the opinions.
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AlkyInMyBlood

stick with the .44 if its not a max effort deal

GOaT Cheese

It is alot easier to set the long block up exactly the way you want it (heads, quench,etc.) and if your DCR is to high or too low you can just move the cam. It is alot easier to advance or retard the camshaft a bit to establish ideal DCR, in my opinion, than it is to pop the heads on and off to try and set it.

GOaT Cheese

Your at almost 42 deg overlap @ .050, even at a DCR of 8.4 I think you may run into a midrange cylinder pressure issue. You are gonna have to keep that engine very cool for it to work on pump gas. This is just a suggestion, I know I'm gonna get alot of jeers for saying this, but you might want to consider retarding the cam a few, say back to 112 or 113 ICL to kill some of the DCR, it will idle alot worse though, and you will lose some low end. That's my 2 cents.

03 BUSA

iTrader: (25)

So you definitley would not go to a thinner gasket for quench? What are the issues I am faced with the midrange cyl pressure? Also, besides a 160 thermostat would you recommend I change from the TR55 to the TR6. Thanks for the help.

GOaT Cheese

I wouldn't, you are already at +.005 on the deck, and acounting for the standard .025 for piston/rod "stretch", you only have .026 left for gitchy room with a .051 gasket.Going any thinner on the head gasket would make me real nervous. And at 42 deg overlap I think the midrange scavanging, assuming you have a bitchen exhaust system, is gonna pull in some serious air charge. I think you may have some detonation at around 4500 and up. Unless you can keep it around 180 degrees or so.

03 BUSA

iTrader: (25)

I am going Kooks 1/78 with no step no emmissions off road y-pipe and an open Borla catback. Again, I really appreciate your help. You seem to know alot about this issue. I would grade myself a mid level of this knowledge but no expert by any means.

speedracer5532

iTrader: (8)

I would go thinner on the head gasket, the tighter the quench the less chance of detonation. If your pistons are .005 out of the hole, I would run an .040 gasket. That would give you a .035 quench. On my 402 my pistons are .011 out and I am running an .040 gasket which gives a .029 quench with no problems at all.

03 BUSA

iTrader: (25)

I cannot run a .040 gasket the DCR would sky rocket into the 8.9.1 range, which optimal quench or not it would detonate in hot weather. The .045 Cometic would be around 8.79.1 which is still very high.

DONAIMIAN

iTrader: (18)

Id go with the thinner gasket (tighter quench) and play around with the cam to get you DCR to where you want it.

SSilverSSurfer

iTrader: (8)

see thats your problem, you spend too much time playing with your cam

speedracer5532

iTrader: (8)

Instead on installing the cam straight up, advance the cam 2 or more degrees and that will lower your DCR. I think it is more important to have the tightest quench as possible than to have a lower DCR. 8.5 to 9.0 is optimal for DCR.

GOaT Cheese

If you "advance" the cam, the intake valve will close earlier, and raise the DCR, not lower it.

speedracer5532

iTrader: (8)

Your right my mistake.

Adrenaline_Z

What if the IVC is tuned for the application?

Why not alter piston volume, or chamber volume and have the quench height you desire?

GOaT Cheese

You are absolutely correct. What you hit upon is called custom engine building. And the guys that are successful at pulling all of those variables together in workable package can make alot of money at it.

Patrick G

iTrader: (14)

First off, you want the tightest quench you can reliably get.

Secondly, I highly doubt you have anything close to 8.4:1 DCR with that late of an intake valve closing point. What are the numbers at .006? That's what counts.