I ran across this link while looking around the other forums of the board. I thought it might be informative for those relatively new to the FE forum that dont understand quench and dynamic compression just yet.

Here's the link: http://www.popularhotroddingweb.com/tech/0311_phr_power_squeeze/

I found one paragraph particularly informative, as I've been preaching this for quite some time now:

A cool charge may be the first step toward utilizing a higher CR, but what happens in the combustion chamber can make or break any such efforts. A prime factor here is never to loose sight of the fact that the faster the charge can be burned the higher the compression the cylinder will stand. Chamber cavities between the piston and the cylinder head between about .060-inch - .120-inch appear most likely to be the site of detonation. Speeding up combustion mixture motion/agitation is vital. This means maximizing the quench action. On a small-block Chevy with a stock block height, a stock compression height piston is typically .025-inch down the bore. With a .040-inch gasket this makes the static quench clearance .065-inch, which is way too wide. By cutting the quench clearance the burn rate and quality improve to the point where the motor gains compression and is less likely to detonate even at the higher ratio involved.

This applies to FE's like this:
With the typical 390 build, with 360 pistons, the pistons are about .012" down the hole at TDC, as measured in my 390 using L2291F30 pistons. Use a Fel-Pro .041" head gasket, and you have .053" quench space, real close to the .060" to .120" he sites above. Use a .020" steel shim head gasket, you drop it to .032", much better. By looking at the part I marked in bold, you actually have LESS of a chance of detonation with the thinner gasket and higher compression!

Now look at the 360 motor. .104" deck clearance at TDC. This is why we convert to 390's.

Read the whole article and think about how this applies to FE's. I think you'll find it interesting.

 

you can pull off a tight quence as long as the cam, dynamic cr, and octane,and timing are right.


i sure wouldn't build a 390 with a .030 quench, stock cam, 89 octane, 16L slot dizzy.

 

its strange i hever hear about expansion rates and operating cr. Vizards .025 clearence or whatever it was, kissing the head at 7000rpm. That's a slight increase in compression there.

 

It looks like we can get away with tighter quench than I had previously thought. In an FE with stronger rods than the SBC, spinning slower, we could probably go even less than the .025" he's using, right?

The point that I was trying to shed light on, was that when everything else is held constant, tighter quench will more than compensate for the increase in compression it causes.

 

ametuers barely know what parts to use let alone think about advanced subjects.

I wonder if there are any other dynamic cr and fuel requirements charts.

 

i wouldn't be surprised if a zero deck and .020 head gasket could be used. You would want somewhat tight bearing clearences, 5000-6000rpm limit.

How do those hyperpeutics compare to forged pistons as for exspansion?

 

Forged pistons would expand much more. Hypereutectic pistons fit real tight in the bore. I'd limit it to .030" with forged pistons. At .020" with forged pistons, on a cold morning one good rev could cause damage.

 

Thats why I'am building the 433 with a zero deck and Mr.gaskets .032" Gaskets,and I think with just over 10 to 1 cr, I'll be just fine with the quench and the anti detonation groves in the Probe forged pistons on pump gas!!

Now I'am back to looking for new Heads sometime after Christmas!! I got an offer on the C4's Sunday afternoon I just couldnt refuse!! So now back to the drawing board!! LOL.. Awww Geez!!!!

Russ

 

almost seems predictable who was going to post.

 

Russ...I beat you this time in that I sold the 427 block before you sold the heads. Do I hear aluminum heads in you future?
.....=o&o>.....

 

Yeah Matt, almost predictable Huh!! LMAO!!

And Carl....I tell you I had to think Long and hard about selling them..They were some of the nicest Iron Heads I have seen...But with that said....the guy who bought them..kept making the deal sweeter and sweeter....and for what I had in them...I really would have been stupid not taking his money!!

And yes your right Aluminum Heads are in the 433's future! Which one's yet? I dont know..

I sure like the BT's..and they flow great ported..what I dont like about them is using special Roller rockers from Doug....PumpBuilder...they are pricey!!

I also Like the Dove Canadian Head...But I have also read about passed Purosity problems? So I'am still up in the Air....And I wouldnt be able to swing any until this summer anyway..We Just spent $2500 to send the wife out to SoCal for her Dads Funeral... So Back in the Poor house I am!! LOL

Russ

 

Sorry to hear about the passing of a family member, treat the wife with extra love. The pain lasts a long time, my dad's been gone for three years and he still tells me what i'm doing wrong when running the lathe. Take care as a motor can wait until you get the "perfect build".

.....=o&o>.....

 

i aleays shoot for around .040 not maximum but still safe and seems to work very well. trouble is most factory engines tried to be close to that number but a rebuild and thicker felpros always add alot to the quench distance. My engine ran great i repaced the heads and new gaskets and now she pings like crazy not an uncommon scenario. best bet is milling the heads to compensate for the extra thick head gaskets if that is what you are going to use

 

Milling the heads doesn't compensate for anything. You'd need to mill the block to get the quench distance back. Bad solution IMO. Just get the correct gaskets.

 

Thanks Carl for the kind words...Yeah, its going to take some extra attention..to help her pull thru..(Daddys Girl) But his new wife took all the money to take care of her Daughters..and thats written in stone? So Back to Poor house we go!! LOL..

Russ