Anybody use Speed pro Flat top Hyperutectic pistons? Pn H336CP30 for .030 over.
I am considering a set I saw on Ebay for $140.

my concern is their weight of 624 grams. how does that compare to the stock piston weight? Which I don't know yet.

Can they be put in without rebalancing the rotating assembly?

 

The pistons should be fine to install without rebalancing the engine. They should be stock weight unless otherwise specified. You can double check by phoning the Speed Pro tech phone line in Bangalore (or wherever they are).

 

Why wouldn't you want to have the crank balanced? Based on what's in your sig line you're going to be turning some revs.

I'd go with forged pistons if I were planning on running NOx, but that's just me.

 

Sorry, I should have explained, Different Motor. That motor (avatar) is already assembled for a '79 F-150 toy. That motor was balanced and the crank bearings blueprinted.
This motor is for my '84 250 plow truck, started out as just a ring and bearing job that has evolved into Edelbrock Performer motor w/ GT40P heads. I have about $1300 in this one and am starting to feel like I should replace the slugs.

I pull 12,000# boat and the stock 351W was always Matted to the floor. So I thought I'd up the cam a bit. Next thing I know after some beers, I have a new cam & lifters, a used 600 performer carb & Intake, and GT40P heads coming. Oh yeah and an Angry Wife. HOT ROD PLOW TRUCK HUH?? . Yeah, but Honey our boat is so heavy!!

Crank looks good, so I'm dropping a set .001" bearings in it, to tighten it up a bit.

I weighed a stock piston to be 647.7g where as these Flat top Hypers weigh 624g. I'm not thinking that is good - 24 grams.

Since I started this thread, I talked to the guy who balanced my last crank. He said the Speed Pro's run light. Guess he was right. he also said we might be able to make up the difference with some heavier pins. otherwise another 250 bucks to balance. No wonder she wants to keep me in the house.

Beanscoot,
I called Jegs cuz I could't find a Speedpro tech line. He said they would go right in too. But now that I wieghed them, I'm not think so. At least not without heavier pins or a balance job.

 

if you plan on running headers it will be a challenge with those heads.

if your towing and plowing i would recommend gears more then additional mods to the motor which may impact its reliability.

 

Excellent point on the gears, I have 4:10's to replace the rear with when I put the TruTrac in (currently 3.50's). But I'm still looking for a set for the front

 

i would rebalance the engine, the old trw/speedpro forged pistons are considered heavy but you are looking at the hyper pistons.

 

also what comp rato are you after. anything above 9.5 with iron heads is sketchy on pump gas

 

for small camshafts yes, but the dynamic compression is more important figuret han static compression. If you get around 8.5 and up dynamic things get harry.

 

I understand that GT40P have a 59cc chamber. Also when replacing a 65cc with a 59cc causes the CR to increase .6 ( must be true - I read it on the internet). So that is approxamately .1 increase in CR per 1cc reduction of chamber volume.

These pistons advertise to be 9.14 CR with a 60.4cc head. and these heads are 59 then I should end up with 9.28 CR.
But will verify the compression Ratio during the assembly.

The new pistons showed up last night and the wrist pin is quite a bit thicker than the stock one.
So I took them to my work's lab and had them weighed with a good scale.
Old Piston and Pin was 789.7g total
648g piston + 141.7 pin
New Piston and Pin was 790.9g total
641g piston + 149.9 pin (piston advertised 624g)

1.2 grams over 790grams = .15% difference

So now I feel a lot better about just using them.

As far as the header fit issue, man there's alot of controversy on the subject. Looking at some pics and I read that there is one of the rear plugs gets close to long tube headers. I'm gonna try it. For now though, it will have stock exhaust manifolds, so i hope there won't be a problem. I'll probably learn the hard way. That seems to be the best way for me. a little dense.

 

we've all done it that way from time to time.

 

I dont think you are going to get away with stock manifolds. I have ran the summit branded shortys, and the stainless ford racing shortys. The summit ones cleared the spark plugs better, requiring only a slight dent on #8. The Ford racing ones required a big dent and a $13 spark plug on #4.