[Speargun]

I'm putting a 400 together and will end up with a higher SCR than I wanted and was wondering just how much I could lower it with thicker head gaskets without causing problems.
Right now I'm looking at a hair over 10:1 SCR & 8.78 DCR with a Summit 2801 cam.
I was trying to go for a high 8:1 or a low 9:1 combo for around town driving & dependability using parts already I have.

Here's the combo:
400 +.030 so - 4.15"
16 heads CC'd @ - 72cc
Icon dish pistons - 14cc
Head gasket - .040"
Head gasket bore - 4.181"
Deck clearance - .012" ABOVE the deck

This is where I ran into the issue. I had planned on the pistons being .003 below the deck which would have put me in the mid 9:1 range and at the upper limit of what I was trying to build.
A .062 head gasket would bring down to 9.5:1scr & 8.3dcr
A .072 head gasket would bring down to 9.3:1scr & 8.2dcr

Would that much quench area adversely affect the combustion process and cause problems?

[1968GTO421]

What about changing the cam to a bigger one that will "bleed" off some compression pressures?

[ponyakr]

How 'bout 9.52 CR with .060 x 4.3 Cometic gaskets. You'll still have .048 quench.

http://www.wallaceracing.com/cr_test2.php

https://www.jegs.com/i/Cometic-Gaske...2-060/10002/-1

[72LuxuryLeMansLa.]

With this gasket https://butlerperformance.com/i-2445...tegory:1234803 I get 9.8scr with .033" quench.
Choose the right cam and you're in business.

[77 TRASHCAN]

I asked here, a long time ago about a 10:1 400 engine spec, mimicking a 455 10:1 engine similar to Jim Hand's Wagon engine. The 2802 Summit cam, or the Crower 60243 were choices Cliff and others advised. Of course zero decking, and a few other details need to be in place. The carb and dist tune have to be spot on. It can be done.

The 2801 would be a mistake.

[Stan Weiss]

Pontiac 350 ci DCR for CR = 10.0 for different IVC.

Stan

[Speargun]

It looks like the cheapest option at this point would be to go with an $80 Summit 2802 cam which has a 41* IVC. That should bring the DCR down to 8.46......

[77 TRASHCAN]

That's what I'd do. Might look at butlers website for an inexpensive .045 head gasket...

[ponyakr]

"...I was trying to go for a high 8:1 or a low 9:1 combo..."

Going to a longer duration cam is not gonna do this for you.

These guys seem to be recommending that you stay with the head gaskets & CR you have, & buy a bigger cam.

Only ways I can see to lower your static compression is either with a thicker and larger bore head gasket, or enlarging the size of your combustion chambers.

Just curious about your .040 x 4.181 head gaskets. Never seen a gasket exactly like that. What brand & part # ?

If all your numbers are correct, you only have .028 quench distance. .040 - .012 = .028. That's a little tight, ain't it.

https://www.hotrod.com/articles/ideal-quench-height/

By the way, the cheap Fel Pro gaskets are said to be aprox .045 x 4.3. That would keep you from having to copper coat one side of the Butler gaskets, if you are leaning towards them. Me & thousands of other guys have used these FP gaskets for many ears. Never had a failure, on my high CR 455 bracket engines. They all had the small chamber big valve heads, like 16, 48, 62, etc.

https://www.summitracing.com/parts/f...8aAncvEALw_wcB

https://www.amazon.com/Fel-Pro-8518-.../dp/B000C2AF3I

If you do decide to go with a higher duration cam, but don't want the high lift of the 2802 Summit. You might wanna consider a Melling SPC-3. It shows to be 298/310 adv & 224/236 @ .050 lift. And it has near stock lift of just over .400, with 1.5 rockers.

https://www.ebay.com/itm/Engine-Cams...wAAOSwyXFbl1bY

https://www.rockauto.com/en/parts/me...,camshaft,5260

The 2802 Summit has .488 exhaust lift. I assume this will require stronger springs than a Melling SPC-3. So, if you don't need the extra performance of the higher lift cam, you might prefer the SPC-3, for several reasons.

https://www.summitracing.com/parts/s...oaApQDEALw_wcB

[Speargun]

Originally Posted by ponyakr

"...I was trying to go for a high 8:1 or a low 9:1 combo..."

Going to a longer duration cam is not gonna do this for you.

These guys seem to be recommending that you stay with the head gaskets & CR you have, & buy a bigger cam.


Just curious about your .040 x 4.181 head gaskets. Never seen a gasket exactly like that. What brand & part # ?

Milodon 40040 copper gaskets that I bought close to 30 years ago. I don't think they make them anymore.

Originally Posted by ponyakr

If all your numbers are correct, you only have .028 quench distance. .040 - .012 = .028. That's a little tight, ain't it.

The pistons do have a D shaped 14cc dish so they will be close around the perimeter, but should have more quench in the dish... ???

[ponyakr]

"...Milodon 40040 copper gaskets that I bought close to 30 years ago. I don't think they make them anymore..."

I think you have to O-ring the block to run copper gaskets. That's a GREAT reason to buy new gaskets, IMO.

https://www.google.com/search?q=do+y...hrome&ie=UTF-8

[Douglas Willinger]

How about a blend with "E-85"?

[steve25]

Did you confirm that the heads are indeed 72 CCs, as I bet they are closer to 74 CCs,if they have not been cut , or given the normal .003" clean up cut, also if they have been given a valve job then even with new valves being used I would bet that a CC check would show them to be like 75.5 CCs, and more like 76 CCs if the original valves where cut and reused.

If your not running a gapless type top ring then there's another 2 CCs that your not accounting for either for reasons I do not have time to post about today.

Also your not accounting for the cylinder Bore Intake valve notch chamfer that a .030" overbore does not remove completely!

[flat-bill]

subscribe. Billk

[Speargun]

Originally Posted by ponyakr

"...Milodon 40040 copper gaskets that I bought close to 30 years ago. I don't think they make them anymore..."

I think you have to O-ring the block to run copper gaskets. That's a GREAT reason to buy new gaskets, IMO.

https://www.google.com/search?q=do+y...hrome&ie=UTF-8

The block has O-rings, but the head gasket label says that o-rings aren't needed below 14:1 compression.

Originally Posted by steve25

Did you confirm that the heads are indeed 72 CCs, as I bet they are closer to 74 CCs,if they have not been cut , or given the normal .003" clean up cut, also if they have been given a valve job then even with new valves being used I would bet that a CC check would show them to be like 75.5 CCs, and more like 76 CCs if the original valves where cut and reused.

If your not running a gapless type top ring then there's another 2 CCs that your not accounting for either for reasons I do not have time to post about today.

Also your not accounting for the cylinder Bore Intake valve notch chamfer that a .030" overbore does not remove completely!

I've cc'd the heads a few times over the years and they are dead on 72cc.

[tom s]

The Butler gaskets are 46 crushed.Has been my gasket of choice for years.Tom

[Steve C.]

Steve25 mentioned this and it's oven overlooked, the distance from the first compression ring to the top of the piston. The latter will help provide volume above the top ring, but this measurement doesn’t usually affect the final calculation significantly and is used only in very critical applications. If your finicky about details there are some on line compression calculators that deal with that small volume.


.

[footjoy]

Does the #16 head come in two different combustion sizes? I thought they were 85cc.

Thanks

Greg

[ponyakr]

Originally Posted by Douglas Willinger

How about a blend with "E-85"?

I think if your gonna "blend" something with pump gas, it should be either race gas or Torco Accelerator octane booster. E-85 can cause problems in carbs. Don't know how much of it you could mix, without causing serious performance problems, or requiring carb mods.

I realize that some computer controlled FI systems sense the ethanol content & adjust accordingly.

[geeteeohguy]

Originally Posted by ponyakr

I think if your gonna "blend" something with pump gas, it should be either race gas or Torco Accelerator octane booster. E-85 can cause problems in carbs. Don't know how much of it you could mix, without causing serious performance problems, or requiring carb mods.

I realize that some computer controlled FI systems sense the ethanol content & adjust accordingly.

Octane Supreme 130 by Kemco works great as well. It's real TEL.