LB9GTA

iTrader: (1)

I have a 400sbc with a stock shortblock. It has 22cc dish cast pistons and I'm looking to squeeze a couple more hp out of it.

I have afr 195's with a 65cc chamber, so I have about 9.0 compression now

In looking on Summit's website, there isn't much to choose from for a 400sbc.
When I had my 383, I used a steel shim (0.015) and it worked great with lots of bottles of nitrous pushed thru it.

The thinnest gasket I can find is a 0.020. Which would push my compression to 9.3 or 9.4.
This one
http://www.summitracing.com/parts/mrg-1052g

Any steel shims (0.015) for a 400 sbc?

86LG4Bird

iTrader: (1)

IMO, from .020" to .015" isn't enough to ever notice. I'd just run the .020".
If money is no object, contact Cometic; they can do an .015" gasket for you.

redneckjoe

put some flat-tops in there.
probably go great with the afr heads.

LB9GTA

iTrader: (1)

I dont want too spend much more on this engine.

I am putting an aftermarket block 421 sbc in the spring of 2015.
I'm doing a cage this fall on my car

ShawnsRS

How about surfacing the heads? I believe most heads have some extra meat on them ...

LB9GTA

iTrader: (1)

Maybe, but I think that'll cost more than the $100 for head gaskets

LB9GTA

iTrader: (1)

Bringing this one back...

How much can you shave a head before you have to use shorter pushrods?

And how much do you have to shave the heads before its worth it?

1gary

A nice set of heads like that,I doubt I would suggest cutting them for a single build that I intended to replace.Wouldn't you be by far ahead of the game decking the block??.

skinny z

A different pushrod might be required depending on how close you were to having the correct length to begin with. If you were slightly shorter than optimum, then you may fall in exactly where you need to be. Considering that they make pushrods in .050" increments, it'll definitely be something that you'll have to measure to ensure that you're spot on.
As for raising the compression ratio, AFR specs .006" flat milling per cc.
65cc to 60cc will raise your compression about 1/2 a point and will require .030" to be removed. Using a general guideline of a 4% increase in HP per 1 point of increased compression, you may find that it's hardly worth the effort and expense for 10 hp (for a 500 hp engine to start with).
.030" removed from the heads will definitely require another look at push rod length.
Have you performed a compression test? Results from that may help you dial in the compression ratio that best suits your cam specs.

LB9GTA

iTrader: (1)

When I did a comp test it was between 145-150 cold

skinny z

I'm starting to build a data base for compression pressure vs compression ratio. I have most of the info I need about yours except cam specs. Specifically the advertised intake duration and whether you've installed the cam straight up.
Compression ratio, stroke, rod length, adv intake duration, elevation and temperature all factor in. It would be interesting to see how your estimated 9:1 stacks up against 150 psi cranking pressure.

https://www.thirdgen.org/forums/tech...ta-wanted.html

LB9GTA

iTrader: (1)

I replied to your other thread

jokerZ71

If you have a stock short block,assuming stock bore & rods,you should be @ 9.2:1 now w/ a 65 cc head,unless it's been rebuilt w/ short pistons.What is your current deck hgt now.If you have a stock .025 deck hgt,a .020 gasket would have you with a .045 quench which is fine.If you have shorter pistons,you deck hgt could be as much as .045 & even a .015 won't fix that.Decking the block,or'changing pistons would be the only way to correct it.If your on the bottle,do you really wanna raise your CR? 145/150 seems a little low for a healthy 400.IDK your cam specs tho,so,maybe not.

LB9GTA

iTrader: (1)

I'm using a stocker .040 head gasket.
The shortblock is completely stock! When I bought it we re-ringed it and put in new bearings.
Stock dished 22cc cast pistons.
Here's my cam specs
http://www.compcams.com/Company/CC/c...?csid=122&sb=2

I wouldn't say my 400 is healthy, lol. When I got the block checked, it was right on the line to be bored. I chose not to, because this engine was a junk yard build and I didn't think it would've lasted this long or been this fast.

Anything I've read about engines and nitrous was that more compression equals more power.
I have to put new valve springs on before spring, so I figured I would take the heads off and put them on. I also have a small leak on the back of the intake as well that needs fixing

jokerZ71

I just guessed .032 on gasket.You really could use some more CR with that cam,or'use a cam with an earlier IVC.The intake closes so late that your not building the cylinder psi that you could.Your DCR is like 7.5:1.I don't think a thinner gasket is gonna get ya where you need to be.You need to get your SCR up to about 10:1 to raise your DCR up to a respectable 8:1 DCR.To get there,you need a .015 gasket & still lose about 6 cc's either from the piston or chamber.You could advance the cam & maybe help some.

LB9GTA

iTrader: (1)

Do you think that I would gain 10-15 crank hp from a .40 gasket to a .020 head gasket ?
If so, I think the $100 for the gaskets are worth it.

jokerZ71

Honestly,No.I don't think you'll gain that much.Your only raising the SCR by 2/10s.Your DCR is still only gonna be approx 7.8:1.You would gain more by choosing another cam more suited to your CR.By using a .020 gasket & advancing your cam 4*,you could get SCR up about 9.5:1 & DCR to about 8:1.

1gary

LB9GTA

iTrader: (1)

I just did the scr on here
http://www.wallaceracing.com/cr_test2.php

.04 gasket was 9.09
0.02 was 9.48

jokerZ71

Yep. I rounded up to 9.5. The problem is your cam closes the intake valve very late causing you to have a very low effective compression ratio.Since the cylinder can't build psi until the intake closes,your cylinder psi is low.Advancing the cam 4* would close the intake sooner.With a cam that has a late IVC,you need a higher SCR.Your cam is not really matched to the CR you have with the combo of parts being used.

LB9GTA

iTrader: (1)

Agreed, its the wrong cam for this combo.
My last engine was a 383 stroker with 11-1 compression.

I was just cheap and reused the cam on this junkyard build.

Jonesyfxr

iTrader: (2)

Ok, maybe too many beers.....what IVC?

LB9GTA

iTrader: (1)

IVC is 69 degrees.

If it makes a difference, when I race, I use 110 octane fuel when I run nitrous.
I have run a 125 shot and am going to run a 150 shot this summer

jokerZ71

With the heads you have,you could prolly increase DCR between 8.5:1 & 9:1 & still run on 91/92 with a good tune & proper cooling.Getting DCR up will increase your power.Rite now,you're leaving a lot on the table.

jokerZ71

IVC is intake valve close. As the piston comes up on compression stroke,it doesn't build compression til after the intake valve closes.This determines your actual running CR, or DCR.(dynamic compression ratio).

skinny z

Thanks. I'll post up some results when I have time.