in my "limited' builds of the past I never got much more than a MP/DC lm or smec a 314 cam and a little help with things here and there
I had 6 85 G head motors in as many years and Idono , 4 or 5 later motors with the FB head
never got clean plugs out of a FB head yet - always very black and ugly
my G head motors always gave me nice clean very lightly tan coloured plugs (almost dusty looking)- includeing the one rebuilt 85 motor with the 86 style dish (which drove with no notable difference)
(I was doing this way back before A/F widebands .. or web sites lol)
I did have one FB head that ran reasonably clean .. for about three weeks
it was the 86 LW rod motor with a large can TII conversion that didn't work so well as the wastegate would not open (non rebuilt used motor)
that ran on overboost shutdown until it broke - that head ended up still clean, with pink and white valves but no notable piston top damage - something died deeper inside it
of my 3 or 4 LW rod motors that was the only one that failed - all my 85's spun the rod bearings in 6 months
and my one & only roller cam motor failed in the valve train it seems
10 years after it died , a "new cryco parts counter 2.5" / TII conversion in an 87 shelby z I bought , I pulled the head to find a chunk of piston top from below the exhaust valve , stuck in the valve , a roller follower sitting between the springs and a lifter that would not compress ten years after it had last run - all the other lifters would compress but that one wouldn't budge even when smacked with my framing hammer on the bench vice
- that ran for the two years I had it and the time the guy I bought it from had it with the stock TII tuning
that head did not run cleanly either
I have to say I do find posts saying don't even start a 2.5 with a 2.2 LM funny as hell though
I've read that tuning a 2.5 with a G head can be an issue - I'd think maybe it has to do with the very large piston dish vs the G head chamber and the much smaller dish of the 84/5 motors
that large dish , small rim edge also makes me think the 2.5 piston might be weaker above the top ring too
but back to the heads..
I have a couple of questions with regard to the G head
I've read the port roof as it enters the valve bowel is ever so slightly higher in a 655 head - true ?
- measureable ?
I have a 655 head and this "ported" G head I just got so I don't have o-e ports to compare
and , at the manifold surface , exactly what is inside the head just above the intake bolts and the top row of exhaust studs ?
meaning what would I be drilling into if I were to raise the intake bolts by the difference in port height of the regular port vs the 655 port
I was planing to mod the intake for a 655 head so adding weld behind the valve cover rail wouldn't be a streach , thus putting the 655 modded intake on the small port G head with the height differance now being at the top .. and bolt bungs on the intake that still haven't been tampered with so they might not break off
and again for the top row of exhaust studs ? - with the intent to take the downward hook at the opening of the exhaust port , plus some away
I will not be useing the stock exhaust manifold that imediately turns the exhaust flow downward so I don't need the head to be the early start to that change in flow direction
I look at the exhaust ports and see the same change in direction my 460 ford exhaust ports had
- the floors of the 460 port are ramped down so much the bottom of the port looks more like a suggestion of a port
the fix is a Trick Flow head - they raise the stock 460 ex port 3/8 inch
I guess I ask from the viewpoint of a couple of gone over the hill big block . raised port dodge / ford projects and little chance of scoring one of those isma heads lol
I do however already have everything to build an isma valve /pt/beehive/S60 cam, G head
and as I think of it , can I fix the cam center - due to a lack of caps on both the heads I got last week by machining it to take bearing shells ?
if so I have a pair of semi ported heads .. if not , a nice thump in the scrap bin ..