tgensel

I building a 406 for my 72 and have a set of 215 iron eagle platinum 64cc heads. My engine builder (also my friend and racer) says with flatops and a cometic thicker head gasket I can adjust the compression to around 10.7 to 1 which should be good for 93 octane pump gas. His logic is if I ever decide to go racing it would be easy to change head gaskets and get higher compression. My question is should I do this or would dish pistons and a normal gasket be the better way to go.

Ben Lurkin

No, no, NO. You want the quench to be 0.035" to 0.050" max. Failure to do so will result in an engine that is more detonation prone and won't run as well.

Use the proper pistons to get the right compression ratio. It sounds like you're only going to see the track occasionally so leave the compression where you can still use pump gas.

l88rocket

Just put the correct pistons in it, if you want compression put it in it and run some octane booster. Changing head gaskets for a weekend is expensive once you tq a head gasket its junk and cant be reused.

427Hotrod

I just did a 400 with flat tops and aluminum 64 cc heads. 11.0 compression with a 248* solid roller. Runs fine on the dyno and street with full timing on 93 octane.

JIM

L88Plus

^^^Watch out for this guy, he thinks cylinder heads are piston stops
Adjusting compression isn't something to use head gaskets for. Once you open you quench up over about .055 or so, you lose all the benefits of having it at all, you MAY detonate worse with lower compression.

Indiancreek

When you are walking a fine line with regard to ratio and 93 pump gas, be careful. I'd keep some booster with me when out and about.
It is possible to get a weak tank of gas. Risk engine damage.

The Money Pit

The cam will play into this,.......427Hotrod with 248 degrees @.050 shows this, and I'm sure you'll be fine if the cam you select is big enough. I'd go with a decent flat top piston, match the cam for now. Later you may decide to swap heads to better aluminum heads...

jackson

Keep this in mind ... this ain't a 350 ...
last time I looked, and aside from all-copper ,
I found NO thin head gaskets for sbc400 ... some about 0.038" but not thinner. Maybe I missed some; if so, y'all please edjumacate me.

suggest you First choose the gasket you will use,
then deck-mill block to obtain proper quench,
then pick a dish / reverse dome piston (mahle, diamond, wiseco, sealed power, je, srp all good).

most shelf-stock performance pistons locate piston about 0.025" down in hole of an OE uncut deck. If that's your case, suggest zero-deck block & use typical 0.038"-0.041" composition gasket made for sbc400. Later on, and if you ever damage a deck, you can mill it again & run the available thick gaskets.

ask around & see how much it costs for a good tech to convert a performance carb over to E85?
with exception of E85, how many more years is hi-octane pump gas gonna be common?

427Hotrod

I have to agree with Jackson here. Your best to build the motor right and set deck height correctly. If you're already building it, it's just part of the deal. Since you have iron heads, you might want to not squeeze it too tight...but I don't think it makes as much difference between iron and aluminum as people think. Once the chamber is warmed up it's warmed up in real street use. Maybe long high speed runs. Cam choice will make as much difference as anything and a good cooling system

The only other thin gasket I know of it custom Cometics which really are about the same price....but you can get whatever you want from them. If you deck it just use regular gaskets so it's no hassle later.

JIM

v2racing

I agree with keeping the squish (quench) tight, between .035" and .040". There are great benefits there. I run mine at .034" on the engine in my signature. I oiled everything out when I built this engine and it is a true 11.8 to 1 compression. I run it on pump gas. A good cooling system and attention to tuning (far beyond the norm) is essential to run compression this high on pump gas. I wouldn't recommend it for most people. I would run dished pistons and match the cam to the compression. You can get custom made pistons from companies like CP Pistons. You then can run the exact compression you after. I would probably shoot for 10 to 10.5 with a cam in the 240 to 246 degree range on the intake.

tgensel

Thanks all:
The block has been decked with the pistons 5 th in the hole (I think). My engine builder has the computer that calcs the compression we just enter all the components. Dished pistons are available and I plan to run as big a cam as I can comfortably run on the street. I'm ordering pistons tomorrow so I'll figure this out tonite.

tgensel

I 'm confused! wouldn't a dished piston create a bigger "quench"

MotorHead

Does your engine builder know how much Cometic gaskets cost ?

The comment about not finding a thin gasket for a 400 is true, I had to go with a 3 layer MLS Cometic gasket and it still wasn't very thin

427Hotrod

The quench area is over under the flat portion of the head that hangs into the bore area. The sump/dish will be under the valves themselves on the better pistons.

JIM

L88Plus

As Jim said, the quench area is where the flat part of the head corresponds to the flat part of the piston. The idea is that the fuel/air mixture is squished out of this area at TDC (since ther's only .040 or so clearance) which helps with fuel burn among other things. That's why a true reverse dome is better than a dish. The quench area on a reverse dome corresponds nearly exactly to the quench area of the head - the heart shaped chamber is adjacent to the heart shaped "dish" on the piston. A true dish has very little quench, the recessed area of the piston is shaped more like a saucer.

v2racing

I should have said reversed dome in my post. I would never run a true dished piston.

tgensel

OK I'm going with a reverse dome (-16cc) srp piston. Pistons are 5 in the hole. can anyone give me a part number on the best gasket?

v2racing

This is a .038" Mr. Gasket head gasket from Summit. MRG-5801G

It would be better if you could have a zero deck.

tgensel

already been decked. plan on using srp 147549 and ring kit j 100 f8-4155-5 but I have read this is discontinued by part #271069.
is this true

Ben Lurkin

With .005" in the hole, this equals 0.042" = just right. You won't get any additional benefit by going tighter.

Good choice. JE still lists them on their website. Suggest you call Flatlander Racing for best $.