Although I am aware that popular opinion states "quench" should be from .035"-.045" i'm sure there is much debate.

I recently pulled the heads on my 406 to do some additional port work and to minimize my quench. After calling Cometic today I have decided to shoot for .040" quench and get their .030" MLS gasket. This is with a .010" deck height. This would yield a 10.47:1 SCR and a 8.0277:1 DCR.

My question is would it be worth it, or just too risky to run a .027" gasket for a total quench of .037". This would yield a 10.55:1 SCR and a 8.0817:1 DCR.
This difference is negligible, but I would like to optimize my quench just short of being **** about it. :lol:

I am going to get a deck bridge to confirm each piston's exact position at TDC.

Think .037" would be flirting with disaster?

Heads are AFR 195 with 74cc chambers
Pistons are SRP flat tops, 5cc relief
Steel H-beam rods
.0034" main bearing clearance
.0022" rod bearing clearance

Hopefully I will get these ordered within a few days.
At $160 a set you don't want to order the wrong thing! : :smash:

Thanks! :cheers:


[Modified by VETDRMS, 9:39 PM 2/9/2004]

 

Well, to begin with, I like tight quench. For example mine is at .028 with a 4.5" bore, so you can imagine how tight things get in there with a little piston rock. My pistons are OUT of the bore .009 and gaskets are .037 compressed. Now I can tell you that is about the limit for mine. When I had the chambers stock, the pistons were just barely missing the head. I mean like you could see the clean spot on the head and piston where the were just kissing. No damage and it was only on one bank...the one that is .0005 (half of one thousandth) shorter than the other. When heads were ported the chambers were opened up so it eliminated that area, but I'm still using the same quench distance.

Make sure of your measurements. Take measurements on both sides of piston as you "rock" it back and forth. You have to allow for piston rock.

I've also found that many gaskets don't compress exactly as the specs say. When you're setting them this tight, you have to be sure. You can take a feeler gauge and check around the head to get an idea when head is torqued on. You might be surprised at what they actually are going to.

Are you spraying LOTS of nitrous? That sure seems like a LOT of gasket for an engine at this HP level. Seems like way overkill. Maybe I'm cheap, butit sure seems like a lot.

I'm using ( as well as some of my National record holding buddies) Ferrea head gaskets that cost like $17 each or something like that. Never had a problem at over 800 HP.

Reality is, that you will not notice much with the tighter numbers, but at least shoot for the .035. I think to push it tighter falls in the "can't hurt" category. Mine is at 11.06 compression with no problems running 93 octane even in Houston heat. I think tight quench is helping me.


JIM

 

Wow, thanks for all the great feedback.

I am aware the gasket is most likely overkill, but I mainly chose them because of the available thicknesses. From what I can tell I can only get the Ferrea gaskets in .035-.045". Being that the pistons are .010" in the hole I need a much smaller gasket. I think I will go with the .027" gaskets from Cometic which will put me right at .037" :cheers:

The price hurts, and I do plan to run ~150hp nitrous this summer so its just added insurance. I am also considering milling the heads a marginal amount to clean them up and to get another 1/4-1/2 point. I just don't want to get into detonation as only 91 octane is available here. Although I am at 3500-4000ft elevation so that will help. The track I plan to race at is at 4000ft. :cry:

Thanks again!

Also, as I forgot to add I am not runnig a LOT of cam. 236/242 @ .050 Hydraulic roller. Do you think 10.75-11.00:1 would be doable with this cam? On 91 octane that is. I am considering switching to a solid roller somewhere in the 242/250 range this spring and I'm sure it would run well with the extra compression. Its just the $$$ hit from using this HR for barely 2500miles!, this motor is practically brand new...but of course its no fun if things aren't changin!

Also, Cometic informed me I need a 60RA finish for "proper" seal. I didn't have any problems with the FelPro's, and I don't know my RA currently. Should I check into this before ordering?

Thanks again, much appreciated. :cheers:




[Modified by VETDRMS, 11:26 PM 2/9/2004]

 

You can squeeeze them really tight if you want to with flat pistons and tight wall clearances. I've seen engines run in the .025 range, but it's probably too close for comfort.

The Cometics will give some insurance with the spray. I think you can sneak up on 11.0 with that cam. It looks like a pretty loose converter, so that will help as well as your altitude. But there is a limit. I would much rather have 10.5 and run full timing of say 38* vs. having 11.25 and only running 30* due to detonation. I think altitude will help more than anything.

It's going to be tough to check your RA on the block unless you can borrow some tools.


JIM

 

Piston to wall clearance was .0025" as per SRP's recommendation so they are pretty tight. I noticed some very faint scuffing in the cylinders, but I don't think it is abnormal. My Mighty Demon 750 had a persistant fuel leak that would empty the fuel bowls into the intake, and thus some cylinders when the motor was shut off. After 5 weeks of "repairs" it came back with the same problem. So it is currently on its way back for "replacement." Hopefully the new one won't have that problem.

The closest I can go with the Cometic gaskets is .035"
The converter is quite loose, reminds me of the acceleration of a power-boat.
Feels almost like a CVT. :lol

My machinist (read: friend) has offered to help and I'll run all this by him. He'll be able to confirm the deck surface. If I were to trim .008" off the heads I would be at 73cc chambers, and with the .027" gaskets would be right at 10.66:1 with a DCR of 8.164. Sounds about right. :cheers:

What plug would you recommend running? I was thinking of starting with 1 heat range cooler and going from there. Most likely Accel U-groove.

 

The minimum head to piston clearence, *I* keep reading, is .035" - .040". *I* don't see anything wrong with .037". Anything less than .035", is "experimental", in my mind. It has been pretty well established that one point of compression is worth approximently 4%. I wouldn't go nuts over maximizing the CR, but quench IS important. Quench can discourage detonation. Shaving the heads will only serve to raise the CR, something I'm not convinced you need to do. Why don't you shave the block, and kill two or three birds with one stone? You can establish the surface finish, raise the compression, if you want, and go to a more common, economically priced gasket. The savings in the cost of the gaskets, alone will pay for half the decking. Good luck, and...

RACE ON!!!

 

Just an FYI, on my 406 I am using the Cometic .027 with a .015-.020 with piston rock in the hole. I know its borderline "OK" quench but I was told that my I-beam rods could stretch at 6000+rpm and to not chance it with more than a .015 deck on my engine.

My Static is 10.94 and my Dynamic is 8.41

EDIT, I used the .017 as an average for the dimension "in the hole". So I should have .044" quench


[Modified by ld85, 4:18 PM 2/10/2004]

 

Ah, where did this SRP recommendation originate from? The user pamphlet included in box, with the pistons?

 

arnold The "exact" number is burried with some other papers, but I will dig it out. From memory I believe it was .0025". The specs were on SRP's phamplet, but I was aware of a typo a typo at the time, or something like that and I checked with SRP. However at the moment I can't recall what that typo/error was. Do you recall?

:cheers:

 

The sheet included with the pistons, state IIRC appr. .0025". That is why I asked, because that is incorrect. The correct specs to build to need to come from SRP phone contact, or from their website. What it amounts to, the specs noted on sheet are too tight for proper operation. For me, it was necessary to ignore the recommended clearance noted on sheet. The scuffing noted in your post, may well be due to the rings, though.

 

Thanks for all the great input and help. I just ordered the .030" gaskets and they should be here in a couple weeks.
This will yield a .040" quench, with .010" milled off the heads static compression ratio will be 10.61:1. And DCR will be 8.13:1.

Thanks again, much appreciated!
I also ordered some Titanium Retainers...

 

Vetdrms,

How much were the Cometic head gaskets?

Deen

 

My .027" Cometics were $140 a pair.

 

They were $72.58 each directly from Cometic (800-752-9850).
Plus shipping of course. The lead-time is based on the shipping rate.
Ground has a production lead time of 1 week, 3-day 5 days, and so on.
I was told by a tech to get 3 day so I did. Not sure how much that is
going to add to the cost.

The part number for SBC with steam holes and 4.165" gasket bore and .030' thickness is:

H1076SPA030S

The last 4 digits represent the size. As a .027" thickness would be:

H1076SPA027S

They should ship next tuesday, I will probably get them the same week.

:cheers:


[Modified by VETDRMS, 8:13 AM 2/12/2004]

 

VETDRMS, Id85,

Thanks. I guess I'll take the chance and order a set. I was going to O-ring my block since I'm stepping up to a 671 blower and will be running between 14-20 lbs. boost. It will save me the cost of O-ringing and I've been told you can run more boost than that with the Cometic gaskets. Does anyone know if they are a reusable gasket?

Deen

 

According to Cometic they are reusable up to three times. They said as long as it looks like it did when you first put it on and is not damaged it can be reused. For proper sealing I was told I needed a 60RA finish.