koji tachi posted:
Anyway My friend must decide if he uses this 289 block or replace it to the 302. I will give hime advice to use this 289 block, because some mangusta had been built with 289 block. It is not a wrong combination. Does this make sense? If he decides to continue using this 289 block, he also wants to replace the cylinder head. What is the best choice for cylinder head? PANTERADOUG said the uses the AFR 1388 heads that give good flow in chamber. Does it need be shaved to have the same chamber volume? And I can find the so-called overhauled cylinder heads in low price in ebay. Is it a bad idea to use them.
The AFR 1388 heads use a 2.02" intake and a 1.60" exhaust. You can not use the stock pistons with it. The piston needs a larger cut in it to clear the valve head.
The J head will measure out as 53cc's. The AFR 1388 comes with a 58cc chamber. There are two choices to make to maintain the stock 10.3:1 compression ratio.
1) reduce the size of the 58cc combustion chamber of the AFR 1388, or 2) change the piston to reduce the size of the combustion chamber.
You can also use a thinner head gasket such as the Cometec which is .027" thick. The caution there is that you must have a MINIMUM total of .035" between the top of the piston and the bottom of the cylinder head. If you don't, you will get piston to head interference.
My piston is .013" down in the hole and the head gasket is .027" compressed. So I have a total clearance of .040".
You can buy the head directly from AFR already shaved .024". That would make the chamber 54cc. You can't cut that head any more then that. You will be into the valve seat.
After they are cut (milled), then all you have to do is bolt them on. They are a direct replacement with the exception that they will have an adjustable rocker arm. The J heads rocker arms are not adjustable. You just bolt them on.
The J head has pressed in rocker arm studs. The stock valve springs are on the weak side and will only provide enough spring pressure for 5,000 to 5,500 rpm's. If you change to stronger springs, the rocker arm studs will eventually pull out of the head.
You need to change those to the screw in type, that will also make the rocker arms adjustable.
If you buy used 302 iron J heads, make sure that they are marked 4v. Many sellers are selling 2V heads as 4v. They are not the same. The 2V's have larger combustion chambers and will give you something like 8.0:1 compression. They conveniently get "confused" over the C80E castings on the bottom of the head. Both the 2v and the 4v have that same marking. You cannot mill the 2v heads down enough to get 53cc chambers.
Low cost? They are heavy. 55 pounds each. By the time you ship them, then have them rebuilt, and have the pressed in studs changed over to screw in, they won't be cheap.
They have terrible flow numbers stock. 180 on the intake. 80 on the exhaust. IF you were to take them to a professional porter, the best of them are only able to get about 215 on the intakes.
Personally I think, if you want to build an original engine, then you need the original casting dates. Otherwise the engine isn't original to me?
If you are trying to sell me that car as "original", I want to see pictures of the engine while it is apart and I want to see the casting dates. I'll allow updates like bigger valves, better springs and screw in studs with guide plates but the casting date better be in the correct vacinity ...for me.
Some of the '68 J casting dates are from June and July of '67. For an "original" 'goose, try May or June of '68?
What is wrong with the heads that you have now? Can't they just be rebuilt?
Again. It all depends on what you want. If you are building the engine for resale value, good luck. Every buyer is going to have different criteria. Build the car for driving enjoyment. Let the next buyer grumble about what they don't like. It will always be something and often just a negotiating tactic. No one is going to find a Mangusta just around the corner. No way. Are you building a museum piece that is too valuable to drive?
With a rare car like a Mangusta, you have to buy what is available.