Quazz

iTrader: (1)

hello here are some specs.

The heads are AFR 210 eliminators with 65cc chambers that we are going to angle mill down to 55cc. My Piston to deck clearance is .020, with 16cc Mahle pistons (inverted dome). My current heads are stock castings with a verified chamber size of 53ccs. Stock style valves. Drop in springs with enough seat pressure for the cam, and 1.6 roller rockers and 7/16th studs. Stock length pushrods currently with guide plates

Now, the current CR is right at 10.49:1. I would like a bit of a compression bump ideally, but as long as I can come close to the current compression ratio I'll be happy. I think Ive read that the ideal squish area for most motors is somewhere in the range of .035 to .040 to keep quench correct....

SO here is the issue. What head gaskets should I be looking at to acheive this. if possible?

The motor is a fully forged 383 Stroker, Mahle pistons and rings, a GM847 cam, ect ect. Let me know if you need more information.

bowtienut

iTrader: (1)

Get this one, use your existing LT1 gaskets as templates to open up the required LT1 cooling passages, and you'll get about 11.0:1 CR.
http://www.summitracing.com/parts/fel-1094

Quazz

iTrader: (1)

whew.... at .015 thickness, I'd have a total of .035 clearance between piston and head.... is that enough? I know thats cutting it close for proper quench..

bowtienut

iTrader: (1)

If your .020" deck clearance measurement is accurate, and that's your highest piston, then yes, .035" quench clearance is ideal.

Quazz

iTrader: (1)

Yep, thats accurate. how hard is it to cut those shims out for the water passages? and does it matter if i am running head studs with them? I'm assuming by the calculator Im using that with all that info, and the heads milled to 55CCs, i'll be right at 10.9:1 CR.

NOW the big question is this.... how good are those Felpros to run on the street? The car sees the track MABEY once a year, the rest is daily driving and screwing around for the most part. It also looks like using the .015 shims as opposed to the stock gaskets would net me about 6/10 point on compression. How much power (roughly) does that work out to?

97 6speed z

From the "ole" SBC engine builders "Rule of Thumb" ............. "for naturally aspirated small block Chevy motors in the 350 to 500 flywheel HP range ...... each FULL point of compression ratio increase results in an approximate 3% increase in flywheel HP".

For your specific case, (i.e. with a projected 6/10 of a point CR increase):

(.6) x 3% = 1.8% increase in flywheel HP.

Again, this is just from a decades old SBC engine builders ...... "Rule of Thumb".

Quazz

iTrader: (1)

Hmm. 1.8%.

In all honesty with a 380 HP motor I'm looking at about 6-7 HP with that compression bump.

Not all that much in reality. I could just use the standard gaskets and technically LOOSE that 6-7 HP over what I have now, but make it up easily with decent gains when switching to the AFR210's from home ported stock castings.


Nice to know, and I'm not exactly down to counting tiny ammounts of HP like that LOL.

Quazz

iTrader: (1)

Another thing I should have had done was have the motor Dynoed while it was out of the car and freshly rebuilt.

Home proted heads, stock TB and ported intake. Through a 4L60E and a 3500 PTC stall it put down 342HP and 352Ftlbs of torque. I'm not even sure what I should expect after bolting these afr 210s on... except that it should be MORE. How much.... not sure.

bowtienut

iTrader: (1)

You're missing the point by focusing on that 6-7 peak hp difference.
The difference with poor quench and low CR with that much cam will be noticeable at lower rpms, where you'll need to crutch it with more timing, making it more detonation-prone. Ditch the cam if you don't want to give it the CR it needs to run right.

Quazz

iTrader: (1)

Okay, lets start over here.

The motor is currently a 10.49:1 compression 383 stroker motor with the following:

Mahle Powerpak -16cc inverted dome pistons

53cc stock ported heads

.020 piston to deck clearance.

By using an online calculator, this is what I come up with (provided the gasket bore is 4.1'

With 65cc heads (unmilled AFR 210's) standard .041 compressed gasket thickness, and .020 piston to deck clearance, I come out with 9.3:1 CR

With 60CC heads (AFR's milled -5ccs) and all the above it comes out to 9.8:1 CR

With 60CC heads and a gasked thickness of .026 head gasket compressed thickness, it comes out to 10.1:1 Compression ratio.

With 60CC heads and gasket thickness of .015 it goes up to 10.39:1 CR

With 55CC heads and .041 head gaskets, stays at 10.39:1

With 55CC heads and .026 head gaskets, it bumps to 10.7:1 CR

With 55CC heads and the .015 shims, it goes to 10.99:1 CR.

NOW, the 10.99:1 is a decent boost in compression. The .015 gasket plus the .020 piston to deck clearance equals .035 clearance overall...... whick would put me at teh optimum quench distance correct?

Now, factor in possibly running Nitrous in the future. Should I run different thickness gaskets and a larger quench area just for that purpose?

Honestly, as long as the Compression ratio is at or above my current 10.49:1 I think I'd be happy. It looks like I could acheive that with either a .020 gasket or a .026 gasket. this would net me 10.7 - 10.85:1 CR and a quench distance of .040 to .046.


Is this right?


Is that right?

TravisMcGill2000

iTrader: (2)

Id go with the .026 head gaskets. Why did you go with dished pistons tho? 10.8 compression is really low. Most na strokers run around 12.1 to 12.5 on 93 punp gas

Quazz

iTrader: (1)

Honestly, I left it up to the builder on the pistons. He's very well respected around the area for building rediculous motors. And don't get me wrong, the car flies and makes decent power.

I just talked to AFR, and they are reccomending I angle mill the heads to 55ccs, and use .015 gaskets on it. According to them, that would give me great quench, and bump my compression ratio near 11:1. That should work for running it N/A this year, and hitting it with a 150-175 shot next year.

Quazz

iTrader: (1)

I've been looking around. A Cometic MLS LT-1 gasket can be ordered in a .027 thickness. Thats a compression bump from what I have now to 10.7:1 and a quench distance of .047

How does that sound?

RamAir95TA

iTrader: (2)

I would do whatever you could to get that compression upwards of 12:1. All of a sudden an extra 20HP seems to make sense, doesn't it?

F0x Slaughter

Yeah your builder might build crazy engines but does he build LT1s?
Or SBC/Fs?

10.4:1 is the factory compression on LT1.
Typical SBC 350 has a 9:1.
Guys as stated run 12.5:1 on pump gas, so I think you got screwed on going to dished pistons.

At you 10.5:1 compression you could hit that sucker with like 10 - 12psi.

Quazz

iTrader: (1)

Hmmm.... Blower.......