I want to get my heads shaved to raise my compression. What is a safe amount to take off? Also I was thinking of upgrading to a better distributor, what is a good choice? What is the best way to time my engine for the best performace?

 

Check out the thread here on distributor specs. Save your money and get a reman stock distributor and use the stock DS-II ignition.

You can't take enough material off the heads to make a significant compression increase. The only good way to raise compression is to rebuild the engine with the proper flat top pistons. The Aussie heads you hear about will raise the compression too much. For pump gas shoot for 9.0:1 compression. You can go higher but with age and miles combustion chamber deposits will eventually raise the compression higher and provide hot spots for preignition.

 

You can knock .060 off these heads, but just like Torque1st says it will make an insignificant increase.

I have not heard that Aus heads raise it too much. If I remember correctly they will get you pretty close to 10 to 1 which is definitely alot for iron heads, but I would think that you could manage to get by if you play with the ignition curve and are willing to buy 93 octane if you can get it in your area.

Your other alternative is 4V heads, but there are indeed complications. With those you are back to 10:1 or so and as Torque1st says, that may very well be too high. Other complications with 4V heads include the fact that they are difficult to find and that the ports are so big that you actually have to add weld to the intake manifold and then mill flat and cut ports to fit, big hassle.

The piston alternative is the 71 400 piston that I recently learned the part number for in this forum. I don't remember the thread but it is buried here somewhere. Another piston alternative is 351C flat tops that require machining the pin hole out to the size of the 400 and snap ring grooves cut.

Good luck and let us know what you do and how well it works for you. I am looking to do something to increase CR on my 400 and I'm not anxious to build the engine again so that I can change pistons.

Have a great day,
Doc

 

I am taking them off because of bad seals. From my knowledge they are stock nothings ever been done to them. What are some suggestions on what to have done? I read somewhere before that milling them down abit will raise the compression. Does porting and polishing make a big difference? Is that something I could do myself?

 

What really keeps these engines from coming alive is the lack of compression ratio. Milling the heads won't give more than a point or two at best. It's not worth the trouble.

If you're not going to change pistons or heads to up the compression, then you can break down the heads and use a dremel or high speed grinder to break the sharp edges in the ports and blend everything together carefully. Don't go crazy and take much material, just break the sharp edges.

I do that to most any head that I do for my own engines, but on this engine it won't gain much because these heads don't have a breathing problem to begin with. They breath pretty darn good, the problem is compression. Until you find a way to get about 9 to 1 compression or a little more, the engine will not make lots of power and will feel sluggish. A higher compression engine will almost always feel snappy as compared to its low compression lazy brother.

Good luck,
Doc

 

:-x22 Supercharger!!!!

 

Torque1st,

From my calculations, it appears that with standard 400 deep dish pistons and 58CC aussie heads, you would end up with about 9.4:1. Do you think that could squeek by wiht 93 octane, which is readily available in my area? My gut says it will, but I know that this is on the outer limits.

I have run 10:1 in some aluminum head engines, but the aluminum is much more tolerant of this CR because of its better ability to conduct heat. What is your first hand experience with this?

I can get a set of aussie heads for about $200 plus shipping (no telling how much that is from down under.)

Have a great day,
Doc

 

2 or 3 angle valve job. back cut any edges on the valves behind the seat area especially on the intake. also chamfer the outside edges of the exhaust valve guides.

then do as stated above, go in and just smooth out all the sharp edges and imperfections. they are allready flow nice for stock heads you just want to take full advatage of it.

head gaskets, make sure you get em between .039 to .041" compressed thickness. I've seen some brands as high as .048 thick and that will just take away from any compression you add by milling. flat tops are the way to go.
theseheads have been a hot subject this month so check out some of the other posts.

 

I have read that Aussie heads take the CR to 10.5:1. IAnd I have heard conflicting stories about whether this will run on pump gas.

For me, I didn't want to go that high, so I got the Badger flattops and used the stock 2V heads, milled slightly and poliches real good, and my estimated CR is 9.2:1 I may go with Aussies one day, but not now.

4V heads are great for racing, but have less low-end torque than 2V heads. I got a Edelbrock Performer 400 intake for mine and had to port the intake because the ports on the 2V heads were larger than the Edelbrock ports.

 

If the info I have seen is correct, the regular 2V heads are 78 CC chambers and the Aussie heads are 58CC chambers. If that is correct then with regular 400 pistons, my calculation shows that a 20CC loss in chamber size would give a 9.4:1 CR.

I expect that if you had flat tops AND Aussie heads, then you would be looking at something like 10.5:1.

Have a great day,
Doc

 

I know that is correct on the Aussie heads. I am not sure what CC the stock heads are at. But that is the first I have heard that Aussie heads only take it to 9.4:1. That is cool, if that is right. I didn't get those because I thought they went way over 10:1. I hope I am wrong because I may want to pick some of those up.

 

I am by far not an expert,.....but with a little research you will find that the problem with Aussie 302C heads on a 400 is not the problem with two much compression, its almost the lack there of. Let me put it to you like this, the piston is so far down in the block that it will not make for good compression or quench and could possibly make pinging worse. To take advantage of the closed chambered 2V Aussie 302c heads you almost have to have the piston at zero deck and pistons with a big dish, like around 30cc. I'm no expert, but i've read a thread or million. I have read that some are having luck with the Aussie heads and 351M engine with stock pistons.

 

Sorry, I don't have the time to run thru the calculations for you. It has been discussed many times here.

 

You don't have to run through the calculations for me, I've already done them. The only thing that I'm not sure of as far as the calculations go is the exact combustion chamber sizes. If the 2V head is 78CC and the Aussie head is 58CC then the CR of an Aussie head on a 400 with stock pistons is 9.4:1.

What I DON'T know is the experiences that people have actually had with this setup. Some combustion chamber shapes are more susceptible to pinging than others. It may very well be that this setup would ping even at 9:1 for all I know.

As far as using a 30CC dish, that is roughly about the size of the dish in a standard 400 piston. In a standard 400, assuming the chamber size is 78CC, and I think that is correct, then there is about 40CC beyond that. The pistons are a good bit below the deck, so the dish is probably about 30CC.

I am not arguing here, I am only trying to gather first hand information from those who have actually done it. I'm not interested in reinventing the wheel and I would like to up the compression with a head change if possible rather than fit and change pistons in a relatively fresh engine.

Even if I am right on the money with my 9.4:1 CR calculation, it still could be too much for the quench head.

Any firsthand experience or pointing toward some threads with such information is greatly appreciated.

Have a great day,
Doc

 

The real advantage of running the 2v 302C Aussie heads is the closed chamber design. If you dont have the piston at zero deck then you will have ZERO quench area or squish area. Quench area being the space between the top of piston and head. I've just read thousands of post, so someone with more knowledge than I would have to explain exactly why this quench is preferred.
To make a long story short the closed chamber design with proper quench are more effecient and less prone to pinging. Aussie 302C heads w/o proper quech are useless and probably more prone to pinging even if your calculations are telling you it will be 9.5 to 1. So MOST opt to keep there stock heads and change the pistons to some flat top Ohio Badger. But where money is king a 400 + 302C heads + ZERO decked big dished pistons = Lots of power.

Theres gobs of info on this and it needs to be sifted through, so GOOD LUCK.