Can someone help me decide what pistons to use???

[bdazzgt]

I am putting my car back together after i graduated school. My current setup is 5.0 bored .030 over with the summit stock replacement forged pistons, comp 270 cam 218/224 .512 with a 114 lsa, headman equal length headers, h-pipe flowmasters, t-5 king cobra clutch and 3:73 gears, stock intake and throttle body. a buddy bought the trickflow upper engine kit with the double spring upgrade, roller rockers, street heat intake, 4:10 gears, bbk throttle body and 24lb injectors. I need a mass air meter and new fuel pump before i put the motor back together. A small block also came with all the stuff i bought. I took it apart tonight and it has the keith black 115-030 pistons in it, so now i am debating what pistons to use with my set up, i know p/v clearance may be an issue because of the valves on the heads. I was trying to figure out my compression ratio with each piston and which one would get the best performance, if someone could help me with a decision i would appreciate it, also its nice to be back in the mustang world after being gone for 3 years! woot

 

[bdazzgt]

bump

 

[rd]

In simple terms, a flattop piston is a flattop piston and they will all provide about the same compression ratio. If you want to get detailed, the valve relief volume is the only feature that affects compression, until you get to domed pistons. The compression distance on most of these pistons is the same, and is set to allow them to work in a range of rebuilds that have had the decks milled or surfaced a bit. The calculation is pretty easy except for some annoying unit conversions from cc's to cu in's, etc. The other consideration is where the valve reliefs are, since different locations are needed for say, Twisted Wedge style heads.

Piston selection should be made based on planned usage, ie, normal use, performance use, nitrous, etc.

Forged pistons are going to hold up the best under abuse and power adders. My TRW forged flattops have run 100k miles and a bunch of spray and track use.

The biggest effect on compression will be the chamber size on the heads. That can be reduced by milling the head and also by decking the block surface. If doing this you need to verfiy pv clearance by claying the heads during mockup. A stock 70's ish 302 with flattops and stock 70 cc heads will give about 8;3 to 1 compression. Going to a 58 cc head will get that up in the 9 to 1 range. These are the two common ends of the chamber volumn range.

 

[twistedwankel]

ditto RD = stay with forged flattops.

I autocrossed a similar 306 w/ 10:1 compression carbed 750 with 91-93 pump gas and no issues 350HPest for a number of years. Ran mid 13's with stock economy 7.5 rearend, sticky tires and minor weight loss on otherwise stock 82GT 4spd.

I paid a professional to make the heads fit. The chassis was modified to extra stiff.

 

[bdazzgt]

i just hope that i can clear my new TW heads with the flattops, i just got both sets and i was debating, i wanted to stay with the TRW's because they are forged and i can throw a turbo or supercharger on it with no problem.