2.5F Build advice (For dunes)

[Thebedouin60]

As far as my research goes, you can build a stroker F engine by mating the bottom end from a 2F and the top end from a 3F. I have both engines and was contemplating building a 2.5F engine with an RV cam and MAF internals, but i have some doubts, the first being will it run too hot because of the upped compression? (our gas is 95 octane and thats the lowest, 98 highest) and the second doubt is valve clearance because of the upped compression. I hope to end up with a highly built motor that works well in hot conditions at the end for dune-ing and high rpm for climbing steep sand grades.

P.S. - No 2FE as we never got the 3FE out here in sand land, only carby versions of both engines.

 

[Yspen]

I ran a 2f with 3F carb head and Delta 250S cam for 2 years before putting a 3FE head on there . No overheating - it ran warmer but the car was happy with it.
The head was also skimmed to the max ( 9,5:1 compression ratio) and there was no pinging - used 95 octane . The 3F head with the kidney shape chamber seems to be more resistant to predetonation than the 2F head with egg shape chamber .

 

[torfab]

I would skip the high comp pistons, otherwise it should be solid

 

[Thebedouin60]

Ahh so its been done, my next question is would i run into valve clearance problems if i was to run the pistons because of the upped compression? or would it be better to just build up the 3F and have a more usable power band.

 

[Thebedouin60]

I'll make it simple:

Which is better for a hi-po build, 2F or 3F and the reason for your choice.

 

[RockDoc]

3F will have a lighter rotating assembly, and may be be better balanced from the factory, but I would go for the 2F.

The 2F has a taller piston, so it is more stable in the bore.
The extra length of the 2F rod is greater than the extra stroke compared to the 3F, so the rod reaches a lower maximum angle from vertical than the 3F, this means less side loading on the piston from the rod.
A much greater portion of the 3F piston drops out the bottom of the bore at BDC compared to the 2F, so again the piston in the 2F is held more stable.
The 2F has more displacement.

Balance the 2F, upgrade the rod bolts if you are planning to really wind it up, and make yourself a nice motor.

 

[Thebedouin60]

Thank you!!!!!

and yes i agree with upgrading the rod bolts, i'm going to visit the ARP workshop in my hometown to have some made.

 

[Delancy]

I ran a 2f with 3F carb head

Your 3F head was the +87, correct?