Thread: 702 oval port specs

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702 oval port cylinder specs

valve size

These need some knowledgable work to make serious hp from what I've been told. I'm looking at some myself for mild-mod street performance. What do you know about them?

i had them milled to sqaure them and cut with a 3 angle valve job for 2.19/1.88 valve combo with new guides.i used manley raceflow valves with the necked down stems.i didnt do any port work because i want to evaluate before and after porting.IVE GOT THEM ON A .030 OVER 454 WITH SPEEDPRO 2399 FORGED PISTONS/RPM INTAKE/XE 268 CAM/PROFORM MODIFIED 750DP AND SO FAR I AM OK WITH THE COMBO. ONE THING THOUGH,ON BIG BLOCKS WITH A 1.7 ROCKER RATIO MAKES A CAM SEEM BIGGER THAN IT IS.I THOUGHT THAT I WOULD HAVE MORE THAN 15 INCHES OF VACUUM WITH CAM AND COMPRESSION.

Originally posted by jedi 1
i had them milled to sqaure them and cut with a 3 angle valve job for 2.19/1.88 valve combo with new guides.i used manley raceflow valves with the necked down stems.i didnt do any port work because i want to evaluate before and after porting.IVE GOT THEM ON A .030 OVER 454 WITH SPEEDPRO 2399 FORGED PISTONS/RPM INTAKE/XE 268 CAM/PROFORM MODIFIED 750DP AND SO FAR I AM OK WITH THE COMBO. ONE THING THOUGH,ON BIG BLOCKS WITH A 1.7 ROCKER RATIO MAKES A CAM SEEM BIGGER THAN IT IS.I THOUGHT THAT I WOULD HAVE MORE THAN 15 INCHES OF VACUUM WITH CAM AND COMPRESSION.

This is what one head specialist told me on the 702s:

ask for a 78-80 degree cut inside the seat. This is a 50-75 increase on top without sacrificing bottom.

another said that was too much to comfortably cut from those heads. He also said this: The 702s are closed chamber and will have more compression. What you need to know is how high of compression you want on pump gas. Closed chamber heads don't flow nearly as well as open chambers, nevermind ported ones with much bigger valves. Even running the 781s I have and a point lower compression they will easily make 75 more usable/streetable HP than a stock 702 and be pump gas friendly. Usually the only reason people use closed chamber heads is for resto/originality.

These are my words now. Those are nice heads but they will flow best at high RPM. If you port them I believe you will need a manual transmission or torque converter with something like at least a 280 Comp Cam/equivalent or roller. This means a vacuum canister probably. This means stiffer or double springs. These parts are not user friendly from a reliability or street standpoint.

So they are very nice stock heads to race with if worked on.

I would throw some used heads already massaged on your engine or find some aluminum heads ready to go. You can always plank down the money and get new stuff, too.

Whatever you do good luck.

Best

this is why i used the small dome piston instead of a flattop with the 702s which would have given about 9.0:1 but after the head swap to the open chamber head would have only been in the 8:1 range.with the 2399 piston and 049s ill get 9:1 and better.i think ive got about 10:1 right now with the 702s

Originally posted by jedi 1
this is why i used the small dome piston instead of a flattop with the 702s which would have given about 9.0:1 but after the head swap to the open chamber head would have only been in the 8:1 range.with the 2399 piston and 049s ill get 9:1 and better.i think ive got about 10:1 right now with the 702s

If you are sure of your compression ratios you will get more usable torque and better flow with the 049s with big valves and the same money spent on headwork. If you want more than 9 to 1 then mill the heads, angle cut, yada.

Just an opinion, but if you want more street power you may be happier with the open heads.

Sounds like you are on the right track for you. Good luck and safe, fun driving.

Jedi.1 made the comment about useing a dome on a piston.Whenever possible use a flat top piston instead of a dome.Useing a dome sometimes leads to qunech problems, flame travel problems, more weight.etc.As far as heads an open chamber head is better because the closed chamber head really shrouds the valve a lot.

its a small dome like what was originally used on the 71 LS6 9.0:1 454 engine