Choosing pistons to complement GT40P heads

[Capri306]

Hey all. It's been a while since I've actually started a thread here in the Windsor Power Forum, but it feels good to be back in the motor-building mood.

To the chase: I'm rebuilding the near-200k-mile engine in my '87 Notchback. It's old, tired, and has some rod knock. Not content to settle for a stock rebuild, I'm looking to maximize its potential, but within my limited budget (I'm a college student).

This rebuild will consist of my block punched over 0.030-in., GT40P heads (completely stock, no alterations), Explorer/GT40 upper & lower intake manifold(s), Dynomax or MAC headers, some variant of CompCam, with my 'personally tweaked' AOD backing it up. Okay, nothing in there too special, but that's what I'm working with.

The car already has 3.73 gears, Mass-air conversion, E303 (which will go away), an aluminum driveshaft, MSD 6 box, 65mm TB, 2200-stall converter (this too might go away), huge-ass radiator, underdrive pullies, off-road H-pipe (w/ tabs), Dynomax equal lengths, Flowmasters....you get the idea. All it could pull was 14.3's, but at least it was consistent. Biggest mistake was the mismatch in cam and torque converter.

My question regards the choice of pistons for this rebuild. Unfortunately, this also brings the variable of compression ratio into the equation. I won't mind using premium pump gas at all, but I don't want to have to run timing at 6°BTDC, either! I'm thinking around 10.5:1 will be just about the limit for a reliable daily driver with iron heads and pump gas. I need this motor to have a pretty flat torque curve, due to the variety of driving conditions I'll be using it in (particularly city driving), which is why I'm favoring the higher compression ratio. I need a blessed union of driveability and oh-my-God-I-just-crapped-my-pants feel at WOT. If it helps, I believe my stall will be in the neighborhood of 2800 to 3000, but this will depend upon the cam.

My gut is telling me to call up Probe and pick their brains a bit. If not, just to go flat-top Speed Pro w/ Total Seal gapless rings.

Has anyone experimented with various piston types on these heads with good results? Jeff Chambers?

[Jeff Chambers]

The best set that I had were some custom JE's that along with some creative milling of the heads netted me a nice 13.2:1 compression. That carbureted GT40P motor made 465 on th engine dyno with a .500" 239/244 camshaft, Holley 650 carb and Weiand Stealth intake. Those heads were unported and had stock valve sizes! Seriously though if you're not planning on an all-out attack for HP, I'd consider a forged piston out of Probe's SRS line-up. Good quality, exacting tolerance for a modest price. Beyond that I'd call Wiseco for a two-relief stock replacement, un-dished.

[andy669]

How much do you want to spend? The stinkin Speed Pros are around $350 for a set. They are pretty heavy, but strong. A set of SRP's are around $500. They are a high silicon content piston which is good for street use. A forged JE is around $600. Theres plenty of other pistons out there that will make better power than any of these, but we need to know whats in the budget.

To get 10.5:1 with a flattop youre gonna have to mow your heads down to around 54cc, depending on the valve relief size.

Andy

[Capri306]

Thanks for responding so quickly, guys! Yes, I'm not looking for the fastest Mustang possible built on factory parts (even though that would be awesome!). I'm just trying to build something I'll be happy with: great performance without reliability problems or high cost. I know it's a virtual oxymoron, isn't it?

I just added up the machining costs and the cost of the other parts I'll need for this project. Looks like it'll leave approximately $450 for pistons in my budget, which is a total of $2k.

I looked into Wiseco, Probe, TRW, and Speed Pro. The only one I haven't actually found a price for was the Probe SRS's (which would give a C.R. of 11.3:1). Having a goal of a CR of 10.5:1 to maintain street manners, I think the Summit Racing kit with part number FEM-MHP173-211 sounds like my best bet for a cost-effective solution. It has most of the items I'll need for a rebuild, plus the pistons will yield a 10.13:1 CR. Not as high as what I was aiming for, but still acceptable. If I go this direction, it will leave me enough money for a Lentech valve body or possibly a nice set of roller rockers.

The pistons in the Summit kit can be found on this link right here (they're TRWs) Any advice concerning TRW's? IIRC, they're what Ford used as original equipment in 5.0L's.

Also, any thoughts on my goal of 10.5:1 CR? Sounds about right for a streetable car with 94 octane, no?

[andy669]

Getting cheap on the pistons might possibly cost you a little more at the machine shop when it comes time to balance. I have seen the Speed Pros as much as 7 grams different. If you've got $450 budgeted for pistons, use it.

Andy

[Dark_5.0]

For what you want before I spent machine shop/piston/bearings etc... money I would get a complete short block.

There are good deals all the time if you look around. I just missed out on a freshly built 308 with forged Trick Flow pistons/ All Arp bolts and a trick flow girdle for 800bux obo the other day.

I thought a while back you had bought a 351 block off of ebay.

[Capri306]

I still have the 1973 351W block, and believe me, I wanted to use it for this. However, due to the budget contraints, it'd be too much right now, especially for what I have planned for it. Breaks my heart I can't do the 408 & blower combination, but I'd probably need $10k for that little number.

I would go for a short block, but I don't trust other people's work; it's a personal thing, probably a product of seeing others' work fail on a consistent basis (I work retail parts, so guess how many shady mechanics' work I've seen). Mebbe it's the fact I'm born an engineer (and studying to be one at the moment). If I build an engine, and that puppy pops, I would know I have no one to blame but myself. If I installed one built by someone else and it popped, I'd be going back to them for blood.

andy669: I got a flat rate for all of the work from the machine shop, so it's no biggie that it'll take more time. This engine's not going to see over the factory rev limit of 6250rpm anyway, so total mass isn't critical. However, differentiation between the individual pistons isn't a good sign; to me, it indicates a lack of manufacturing quality control. So I will definitely keep that in mind as I finalize my selection. Thanks for the heads-up on the Speed Pros and for your experience with them.

FWIW, I really like the Wiseco pistons. However, I think I'm limited to choosing between forged and hypereutectic TRW/SpeedPro/Sealed Power pistons by my budget. The forged ones yield 10.13:1 CR, whereas the hypers are only 9.08:1, so I believe that may be the deciding factor right there. Thanks again for the tips!!!