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Author Topic:   HEADS
Dirt Maniac

Total posts: 102
posted September 24, 2002 06:23 PM
I race in a class that has a rule of 70cc heads min.and I have a set of 3998993 which are made in mexico and a set of 3986336 which is best to use and what would you do for a little more power from them.

Dirt Full Roller

Total posts: 67
posted September 24, 2002 09:16 PM
i think i would go with the 993s i dont know anything about the 336s 993s have 150cc intake an 92cc ex.

Dirt Maniac

Total posts: 122
posted September 24, 2002 11:11 PM
The 993's are 74cc chambers and are a heavy casting which reduces failures due to heat cycles, Its a good head 1.94 @ 1.50 valves.

Dirt Maniac

Total posts: 122
posted September 24, 2002 11:14 PM
Do a little porting and polishing to get them flowing and maybe take a little meat off them to get down to your 70 cc limit.

Dirt Full Roller

Total posts: 44
posted September 26, 2002 07:32 PM
I just recently got a motor claimed that had 487's on it (we have an open chamber head rule) The motor I got had 993's on it, with the same cam ,compression set up I had to go up 4 jet sizes in my 4412 to eliminate a lean condition. My assumption is the 993's flow better.

rico 08
Dirt Freak

Total posts: 372
posted September 28, 2002 01:30 PM
another good big chamber head is a 441

Dirt Roller

Total posts: 13
posted October 05, 2002 08:48 AM
Id run a set of 916s if your rules allow it.

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