Impala head gaskets are thinner and help raise compression, but I often wonder about the reliablity because there meant to be used with iron heads though.

 

Impla gaskets work great with aluminum heads. I have had them on my car for over 1yr. dailydriver with quite a few nitrous bottles thru it. I was worried about them not holding up when I first did it but they are great. It raises compression to 11.1 from what I have been told and it's free horsepower sinvce you are swapping the heads anyways. Good luck and give us some #'s when you get that thing going. Later

 

The small increase in compression is nice but I think that getting the better quench would be the "REAL" benefit of going with Impala gaskets ON A STOCK BOTTOM END.

The stock bottom end has the piston about .029 down in the bore at TDC and the stock head gaskets are .051. That places the quench at .080. If you use a Fel Pro (.041) or Impala head gasket (.029) the quench gets a little closer (.070 and .058) to the desired .035-.045 quench height that you want. With the stock piston .029 in the bore, you will not get into the .035-.045 range with out changing pistons but this is as close as you can get and I feel any time you can get the quench better, go for it.

When the quench is not right, the piston comes up on compression stroke and when aproaching TDC it causes air and fuel to be compressed into the chamber AND the .080 between the piston and quench pads of the head. The closer to .035-.045 you can get, the more the air and fuel will be "squished" into the chamber and less air and fuel will be left in between the piston and quench pad. This "tighter quench" causes more turbulence when forcing the entire mixture into a smaller area (the chamber only) and mixes the air and fuel better and makes it easier to ignite. This make sure that more of the mixture is burned and less wasted. This also makes it more efficient so you can run less timing and still ingite the entire mixture since it burns more rapidly and will produce more HP and TQ.

The explanation here might be "sketchy" but I am sure if you talk to a trusted engine builder, they can possibly explain it better. Some might want slightly more/less quench for "their" preference or set up but most will agree that if you can get it from .080 to .059, do it. Even though a tighter quench produces more compression, it is LESS likely to detonate b/c of this turbulence, better mixing and mor complete igniting of the mixture.

IMO, I feel that you should run it as tight as possible with out the piston hitting the head. This will depend on RPM, rod type, etc, since these parts stretch and there is piston rock, etc but on a 6500 RPM, steel rod SB Chevy, .035-.045 is the "target area".

Once again these are "MY" opinions.

NightTrain66

 

For 2200 you could of had alot more for your money going another route..but o well congrats.

 

You and I are going to have to have a grudge match at Carolina Dragway. I say CD b/c SDR and Commerce have no traction, but CD has all the traction we need. that way there is no excuse. I put my LT4 set up against your 306/stock heads since the LT4 route is so bad...if you want to see the 'stuff' on my car check out GAFBA site under this name: Shon Herron.

 

So,

Nighttrain,

In newby terms, What you are saying is that effectively the Impala head gaskets improve what Vizard calls the "squash" or "quench" area, allowing it to burn the mixture more effectively, correct? Does this have anything to do with the compression, and if so am I going to be okay running 92 or 93 octane?

Also, part numbers on the Impala head gaskets would be awesome if anyone has them.

Another question for Nighttrain: Would you recommend polishing the combustion chamber on the LT4 heads? How about the exhaust ports? Or should I just stick to working the valve guide boss area? Also, I've been looking down the exhaust valve port at this boss. When I work it, should I narrow the whole thing down around the edges, or taper it more, or just make it thinnner (hard to describe...)


Ok, thanks for all the help!

 

Kuma,

Yea, squish or quench is what I was refering to. You can find info from Vizard, Yunich, etc.

The thinner head gaskets will increase compression slightly as well. As long as you do not mill the heads, you will be fine on Super Unleaded. I do not have a part # but Combination Motorsport (702-798-8504) and most GM dealerships can help you.

Polishing the chambers might help slightly but unless you have some junk valves to protect the seats, I would not bother.

If you have done portwork before, it is no big deal, f you have never ported anything, you might just bolt em on. The guide narrowing would give minimal gains but if you are used to it, it is worth it. If you are not used to it, you might not help at all or slightly hurt. The heads are really ready to bolt on for most set ups.
If you decide to do it, I would taper it more and make it like a teardrop. I will send you a pic of what I do. Just be careful not to "nick" or "scratch" the seats or they will need a valve job. The guides should be more narrow everywhere but very narrow at the beginning and slowly widen as they they get taller. It is hard to put in words and I do not know what porting experience you have so I will send you a pic to your e-mail address.

NightTrain66