Lynn E. Hanover

Rotor Heads,



What end Irons (without the "O" ring grooves) have the biggest port runners in



stock form. Which Center Iron has the biggest runners.



I need the year and engine model of each, and Part numbers if you have them.



I need to build a monster 12A bridge port for next year.









Thank you.



Lynn E. Hanover

Jeff20B

'74-'75 front and rear, and '83-'85 intermediate. I'm sure others will have differing opinions.

TYSON

Do they HAVE to be without grooves? Couldn't you just fill them with Devcon?

rotaspec

The early 12A centre (we know it as the R5 Tallport) has 50mm high runners. Most of the endplates I have seen all have the same runner size, but the popular one for J-porting here is the 3B early 13B plate because it takes less work to fill the water jacket with Devcon.



As an aside, why not try and find a cheap 13B-RE out of the J-spec JC Cosmo. The runners are enormous: endplate runners are like a 6-port endplate with the material between the 5th and 6th ports removed; and the centre is tallport size. Of course, they have the o-ring grooves, so you would need matching rotor housings. The best housing for them would be from the 89-91 TII. Use a set of 89-91 N/A rotors with the shaft and counterweights from the 13B-RE as they are the same balance but 9.7:1 compression. Have them milled for 3mm apexes if you are going carbon, or stay with 2mm and go ceramic.

That is a recipe for a hell engine if built right.

TYSON

I think he has to keep it a 12A for the class.

White_FC

Funny this should come up I was thinking about this exact same thing the other day.. except I was thinking of doing it to a housing not an iron, any reason it wouldn't work? obviously you need to make it pretty flat... but other than that I can't see any reason it wouldn't work.

TYSON

Do all the coolant passages still line up?

j9fd3s

i think so, cant say i ever checked though

White_FC

Well I just checked my '84-'85 13b housing against my '86 one, they all line up, there are some minor differences though, although I can't see those effecting the performance of the cooling system at all though.



Hmm interesting.. because I have a mint '85 housing that i'd really quite like to use in my '86 engine if there aren't any really bad problems im not thinking about.