I am building a 383 stroker.
I bought the short block used(less than 1000 miles)(1974 block)
The pistons are speedpro flattop forged with valve reliefs(3.4 cc)
The piston is down 0.035 from the deck.
Isn't this a big number?
I measured this today. I used a Snap-on straight edge and a feeler gauge.

I WAS going to use a 0.040 head gasket but with a 0.075 quench and 10.7 compression,(going with AFR 195 with 65cc) aren't I asking for trouble ?

What is the smallest gasket I can use?

 

The smallest gasket i've "found" is .015 compressed thickness. That's what i'm using.

 

I'd verify that dimension, either its not right or something is amiss with the parts. The pistons shouldnt be that far down.

 

You have a point there. My slugs were only .024 in the hole. .015 gasket gave me .039 quench.

 

I didn't deck the block I raced last year and the pistons were in the hole .031". I used a Fel Pro MLS .015" gasket. I'm sure I gave something up, but it ran pretty good

 

What is the part # for that?

Even if I went with the .015 hg and .035 down the hole, would I still have detonation with a 0.050 quench??

 

The gasket I used was Fel-Pro 1094.

I'm not 100% sure on all the pros/cons of quench but one of the issues is the better the quench the better efficiency. I'm sure somehow this works into detonation.
I believe a stock gasket compresses to .039. Add that to my .024 slugs gives me a stock .063 quench. I didn't have detonation issues.

 

The info below reflects the best knowledge I have right now, but it'd also be a real good idea to call a couple of machine shops, & see what they have to say...

I've been researching this a bit for my own 383 build, & the number that I've run across as the "ideal" is .040". If it's greater than that, you're giving up some efficiency, if it's tighter than that, you need to pay real close attention to your clearances, esp. the P/V clearance.

Based on this, I'd say that "Dialed_In's" assembly was pretty close to being "dialed in" as was the .039" that Viprklr reported.

If LB9GTA were to use that .015" gasket, he'd wind up at .050", which isn't ideal, but from what I understand, really wouldn't be horrible either. Another thing to keep in mind is that a 10.7:1 CR with AFR (alum.) heads is roughly equivalent to a 9.7:1 CR with iron heads - which I don't feel is especially dangerous, personally. As long as normal attention is paid to the type of fuel used & how the timing is set up, I'd guess that the setup described should be good for thousands of miles...

Of course, you could always pull the short-block apart, deck the block .010" & reassemble everything for that "perfect" .040", but I don't think it'd be worth it to me...

(Depends on what the goals are for this engine - street/strip car, circle-track car, dragster, ??? If you're in a really competitive class that only allows limited mods, then it may be worth it to try to get every single advantage you can...)

Good luck!

 

Well, I'll pose this question.

Which compression ratio would everyone pick with this engine?
383 stroker
AFR 195 eliminators 65cc
flat top forged pistons

Option #1
Compression of 11.37-1.0 with a quench of 0.050

Option #2
Compression of 10.7-1.0 with a quench of 0.075

On desktop dyno, I would benefit about 10hp more at 5500rpm with option #1

 

Desktop Dyno assumes you can time it without detonation.

 

Barring any hp gain, which compression/quench combo would you pick?

 

Talk about a "lesser of two evils" scenario... Ugh!

Myself, for a street car, I'd tend to go for the lower CR (option 2). Option 1 would mean that you'd have to hope that you never bought gas that had been diluted, or came from a bad batch..

The extra "10 HP" wouldn't be worth it to me, it's just too close to the edge...

 

I use 91 octane gas all the time, would that be enough to save me from pinging?

At the track I use 94 octane.

 

I'd also personally not shoot any higher than 11.0:1. Personal preference unless you really like riding that fine line.
I can't say how my 10.25:1 quench .039 runs yet as it's still waiting for assembly. BUT at the same compression and my stock quench of .063 I had no detonation whatsoever on even 89 octane. I never went below that.
Ideally if you have someone around you with a laptop and datalogging software you can physically watch your knock counts to see where you're at.
[B]Chances[B] are, you should be fine as long as your car is in good tune and your timing is correct.

 

Yea, that piston depth in the hole is pretty normal for an undecked block and speed-pro pistons.

I think .050" is a tad high, but you'd still see the benefits of the quench effect. But at 11:1 you're too high. .070 is flat out terrible, and with 10.7:1 CR that's too much.

I think the 1 point of compression between aluminum and iron is a bit optimistic.

My opinion? You're between a rock and a hard place. Maybe port open the chambers on the heads until you're at the right zone.
Verify the 3.7cc on the pistons, I thought they're usually 5cc.

Is this still going to be port injection? That gives a bit more leeway on high CR due to good fuel mixing. Ditto with knock sensors.
I'd keep a low t-stat in, and set your electric fans to keep it cool. I'd also polish the combustion chamber, and polish the piston tops, and maybe coat the valves. Polish everything you can. Remove sharp edges from the head surface - chamber area. I think these things I mentioned can keep you safe at around 10.5 and a decent quench, you're still too high where you are now.

 

i have been told countless times that it will be more detonation resistant with a better squish and higher compression then with a wider squish and lower compression, but i have no proof, thats just what i was told.

i think LT1's had compression around 11:1 stock.

i ran 10.3:1 on my iron headed 327 with no major detonation issues on 89 and none on 92, the squish was around .060 FWIW.

 

Since I have not used my heads yet(64cc), I might be able to return them and get a set of AFR 195's with 74cc chambers. That way I can still have a quench of 0.050(0.035 piston down the hole and 0.015 hg)
With that head, I would be at 10.3 compression.
Would that be better??

 

IMHO, heck yeah, that'd be a lot better option for where you're at right now. I REALLY wouldn't want to try to "open up" (or enlarge) the combustion chambers on a new set of AFR heads, there's just no way that you're going to make the chamber design any better, & every chance in the world to make it worse.

If you can get the bigger chambers without a lot of grief, I'm thinking that doing so may be a good solution for you.

Again, just MHO...

 

FWIW, I put Dart Iron Eagle 180s with 49cc chambers on an otherwise stock L05 shortblock in my 1994 G10 Van. With the 49cc chambers, pistons at the stock .025" in the hole, and a .016" embrossed shim head gasket, I was at 10.5:1. I ran it with a production LT4 cam which gave me cranking compression readings of 220 psi. With the TBI setup in control and my tuning, it ran perfectly fine on 89 octane with no knock counts and 30* total timing. Made 300 RWHP through a 700r4, stock converter, and 8.5" 10 bolt with 3.42 gears.

 

I just used another compression calculator and noticed the 2 were different.

Here is my specs
speedpro flattops http://store.summitracing.com/partde...0&autoview=sku
65 cc chambers
0.035 piston down the hole on one side(0.030 on the other side)
0.015 head gasket
4.060 head gasket bore
3.75 stroke and 4.03 bore

So what is my compression?
Is it 11.4 or 10.9??

 

It's 10.9. You forgot to include the volume of the valve reliefs when you got 11.4.

 

Thanks Apeiron !

So that's better, right?
So a 10.9 compression and 0.050 quench.

I can use a snap-on scan tool and check for knock counts so I might have to not run as much timing.

 

head gasket bores are generally like 4.155, might bring it down another .1. i think your fine at 10.9ish

 

This one is 4.10
http://store.summitracing.com/partde...4&autoview=sku

 

I would be tempted to deck the block so you can use good head gaskets . Most of the really thin gaskets aren't recommended for use with Al heads . I don't know how thick the MLS gaskets are . I'm using a .028 Victor graphite gasket that's just for Al heads with the pistons .012 down . On my 355 it computes out to 10.49cr .

 

I'd return the heads and get the 74cc variant. I wasn't thinking when I mentioned open them up, I wouldn't want to touch a die grinder to AFR heads - that's sacriledge

I haven't asked yet, but what cam are you going to use? I really think DCR is most important, but assuming you're running a "planet earth" camshaft - I stand by my previous advice.

 

My SCR is 10.2:1 and the pistons range from 2 to 5 thousandths in the hole, the gasket is .041 for alum heads for a quench of .043 to .046, I run on Regular.

 

The cam I will be running is the 280xfi(hy flat tappet). Down the road I will switch to a hy roller.
I will be using a LT1 converted intake too.