Oh my head, dilema

[caen fred]

My bloc is a F54 with flat top pistons, header + twice pice,

 

I have a P90 shaved 0.4 with shims

I have a 1972 US E88 std

I have a 1973 Euro E88 std

 

Should I shave 0.4 more out of the P90 and reshim

 

Use one of the E88 just changing the seats for steel ones and call it a day, or while I am at changing the seats go for bigger SS valves? If so where on Intake or exhaust?

 

I am running 2 SU TBI modified so I will not starve for fresh air (the SU are just 2 big holes!!!! with any fuel I dare to inject)

 

your 4 cents...

[theghosttanker]

The p-90 head has a more modern combustion chamber shape and if you shave it to 080 it should perform significantly better than an e-88 with larger valves.I have used shaved and shimmed p-90's and p-79's for years and and have always loved them. If you decide to shave to 080 then you should be checking on everything:

The valves need to be the ones specified for the n-47 head; they have stems that are 080 longer.

The valve springs need to be shimmed up properly as well.

The lash pad thickness has to be corrected to get proper wipe patterns.

 

A new set of very high quality valves can be found at a very reasonable price if you google "SI valves". If I were you I would keep the p-90 and go this route; you will be VERY happy with the results and I would guess that it will also end up costing less than replacing the the valve seats and installing larger valves in the e-88 head.

[caen fred]

Thanks, so that's one for the P90

[caen fred]

The valves need to be the ones specified for the n-47 head

 

What size would they be?

[Daeron]

One thing that can't be stressed enough is proper piston-to-head clearance at the quench pad.

 

This is a situation requiring some technical description; I hope my phrasing is understandable.

 

The P-90 combustion chamber's perimeter is not a full circle; instead, it is "peanut shaped" as many say. The section on the head that would have been in that circle, but instead is flat firing deck surface, is called the "quench pad." The detonation-resistant qualities of such a combustion chamber design are very dependent on the flat top piston coming very very VERY close to that quench pad..

 

This is from another thread:

Ideal NA motor, for our heads is a DIRECT flat top, no dish, for perfect burn travel, with .022" piston to head clearence with ofcourse a P or M series head.

 

For Turbo motors, you NEED to ONLY have the dish as a MIRROR of the combustion chambers. I build the motors, bore, etc. then I stick EACH piston up to a P series head that has prussion blue on it, and bump each piston to the head while assembled with NO head gasket. This then gives the exact outline of the chamber, and I then cut INSIDE that area, to make sure there are no trapped areas (such as a stock dish piston on a P90 head). I ordered my last set of pistons to be 9/16" thick domes, with a direct flat top so I can machine the correct dish to get my 8.25-1 compresson ratio, and reveresed imaged the chamber on EACH piston independently and cut accordingly. I then go on the inside and lighten up the uncut areas to .200" thick. NO chamber is the same, this is a casting, thats why each piston needs to be fitted to each chamber.

 

So make sure that if you go the shaved/shimmed P90 route, that you take that into consideration. Check the piston pin height and make sure you get a head gasket with the right thickness.

[caen fred]

I am concerned about that!

I will be using the std feelpro headgasket, what are the inputs on that matter?

I need the specific size of the N47 valves for the guys at SI Valves.

btw the exhaust valve is 35 on the N47 and 36 on the P90. If I use the N47 valves should I change the P90 seats?

 

Thanks