What gasket would you recommend? Want to run my engine (409 sbc) on 93 Octane gas.
Zero deck height.
Dart Iron Eagle Platinum 64cc heads.
Bore 4.165.
Stroke 3.75.
Pistons flat tops with 4 valve relief, I think about -8.7.

Would like a gasket that will perform and last. CR about 10:5.1
Thanks

 

Call the guy that built your engine. A steel shim gasket would be nice, but were the surfaces machined smooth enough for that? Also what gasket thickness was used to calculate your compression?

 

Well I'm the guy who built the engine, got the rotating assembley off e-bay, bought the heads and now I'm at the stage of putting it back together. Each time I use a compression calculator I get different CR results. My goal is to get to a 10:5.1 CR.

 

Valve reliefs are considered a positive number in the compression ratio formulas. Domes are negative numbers. I know it seems backwards but that's they way it's calculated. 4 valve reliefs is around 8 cc, 2 cc each.

Looking through the Summit online choices of head gaskets, you only have one choice for that size bore.

Felpro 1010
Composite type
4.166 bore
.039 compressed thickness

Unless you go with a dish piston, there's no way you're going to get below 11.3 compression with those small chamber heads and that bore/stroke combination unless you tried to use a very thick copper head gasket. You would need a head gasket around .070" thick to drop the compression down to 10.5

Some 76cc large chamber heads will unshroud the valves and drop the compression to 10:1 using the Felpro 1010 gasket and the flat top pistons.

 

Thanks for the info, looking into Cometic and Cortec gaskets. Since the bottom end is assembled I don't want to necessarily change pistons.

What about modifying the head combustion chamber to a 72cc?

Installed a Comp Cam XE268H flat tappet cam, .479/.480 lift, .224/.230 duration, 110 lobe seperation, heads have 200cc runners, if I can run 11:1.1 CR on 93 octane with this set up I'll leave it as it is, I just don't want to go to the airport everytime I need gas.

With zero deck height, and a gasket thickness of .039 would quench be .039? Is this good?

CARB/NO ECM/NO EMISSIONS/HEADERS

 

I wouldn't touch 11:1 with iron heads and a cam that small.

I'm running 10.5:1 with aluminum heads and that same cam and it seems okay. Haven't run the motor enough to tune it in and start messing much with stuff yet. No audible knock pinging though so far. I'm using a .039" gasket with a .020" copper shim to get my compression down to 10.5. That's what I get for using 4-valve relief flat-tops and 52cc heads.

 

The copper shim might work out, do you think it's durable and will hold up? .059 should get me into the ballpark. Thanks

 

I don't know what the bore of my head gasket is though, I only have a 350. It was part number 7733PT-2 if I remember correctly.

 

Nope, won't work for you. That head gasket has a bore of 4.125".

 

In whos? In every piston i've seen sold, and every online calculator I've used, a negative number is for a relief or dish, and positive number for a dome.

http://www.csgnetwork.com/compcalc.html

^^ for example..

-- Joe

 

http://home.earthlink.net/~armadillo.../compratio.htm
http://www.carcraft.com/techarticles/982/
http://www.dunegoon.org/compression.html
http://www.blainetech.net/articles/default.php

It really depends on what formula you use but valve cutouts or a dish piston is considered a positive number because it adds volume to the combustion chamber

 

Guess what??? I learned something today, and everybody's right, depends on what calculator you use, used both and came out with the same results. .074 with my set-up will result in 10:46.1 CR. Does anybody see a problem with this thick of a gasket?

No nitrous or SC just CARB. Thanks again

 

Yes your quench is gonna be shot to ****.

I'd that the grinder to the combustion chambers first.

Also try a .03-.04" thick gasket to get some reasonable quench.

 

ok, good info, quench should be around 39-45? So hogging out the heads to 72cc would be the way to go. The .040 or so thick head gasket would be ok? I figure CR about 10:43.1

 

Sounds like you don't understand what quench is.

 

Hey NASTY, what I need is helpful information, as I stated earlier I'm no expert and I need some advice, not critique.

Quench: is the space between the piston and the flat portion of the head.

 

If the block's been decked those thicker gaskets aren't going to kill you. My block wasn't decked, and all of my pistons are between .023-.025" down in the bore, and I'm using a .039" head gasket, and a .020" copper shim. That puts my quench height at somewhere around .072-.074" and I have no problems. However, I have aluminum heads and they are very well-designed chambers for higher compression.

 

Thats too much. I put my pistons .005" into the hole, and ran a .039 gasket.

-- Joe

 

OK, with zero deck and enlarging the chambers to 72/74cc, and using a .039 head gasket I should have a reasonable 93 octane running engine?

72cc = 10.39:1
74cc = 10.19:1

I know these heads can go to 72cc just don't know about 74cc.

By enlarging the chambers I won't have to tear the bottom end down and replace pistons.

How about 1.5 as opposed to 1.6 rockers for increase lift. Would this help me out?

 

You could get away with 10.2cr and 93 if you have the quench optimized.

 

Could you elaborate on this? How do I go about it? Thanks

 

Like you said, the quench is the distance from the flat part of the head to the piston's surface at TDC. The smaller the number the better, but you want to make sure there is adequate room so that the piston doesn't slam into the head.

Stock blocks are anywhere from .025-.035" down in the hole with a .040" gasket. Mine isn't terribly far from stock, but obviously it could be better. Like I said though, I'm running 10.5:1 CR on 93 without problems using a stock 'vette tune and 8* of base timing. Using aluminum heads though. I wouldn't go over 10:1 with iron heads.

If you're going to do work to the chambers to increase volume, take it to a shop. You don't want to just start grinding on stuff because chambers are designed in specific ways for flow/swirl/detonation reasons.

 

Thanks, and no I would never take a grinder to a set of $900 heads, I'll let the expert do that, I think I'll try and get 74cc out em, we'll see what the man says. That should yield a low 10 CR and allow me to use a thinner gasket to get the best quench and get this project going, thanks for your time and expertise, we lay people really do appreciate evryone's knowledge and taking time to keep us on the right track.

 

No problem. Wasn't trying to be a d!ck, but there's more to it than that. It affects a ton of aspects on how the engine will run and you need to learn the basics before you dive into things like quench dynamics, flame travel and squish. Sooooooooooo, what I said WAS helpful information.

 

for the record, its #.#:#, not #:#.# when talking about compression ratios

 

Quench dynamics, no way buddy, I just want to put this engine together, plain and simple, and let me tell you somethin, having a forum like this really helps people like me who have enough knowledge to get into trouble, all we need is a little help from the guys that have been doing this for awhile. Constructive comments are always welcome and I sure do thanks everybody for their time.

 

Who in the hell is keeping record #.#:, ?????
Thats what I mean, focus on the question and provide assistance, don't step on the **** ants and watch the elephants go by. If it was a perfect world????????

 

I've never heard anyone ever use 1 to 10.1 until this thread.

 

Man you need to chill the hell out. People are trying to help you. Just calm down and listen to what they're saying, BUDDY

 

Miss-type?

 

No, no miss type. Thanks.

 

Ya I know, I don't think he reads the thread and fully understands what is being said, anyway, ME Leigh and Duron Clocker THANKS I really do appreciate all the help, now to make a decision and get to work. Chow