It's a long story, but I try to tell it short.

I own my '89 E150 with 302 for 5 years now.
A friend of mine has the same model with the same engine - and it feels a lot stronger.

Recently I tried to convert my motor to a roller cam.
I don't know what happened, but after running for about 10s the engine stopped, the camshaft bolt was stretched and the cam-pin was snapped off.

Got a new bolt+Pin and before I assemble everything back together I wanted to check the compression.
Turned out that on 3 cylinders were none, because the valves kissed the pistons.
I also putted oil in the cylinders to check if it runs past the piston rings - unfortunately it did
Than I tried to move the pistons to left and right - and almost all are tipping.

So now I've looked around for a new set of .030 overbore and now I'm overwhelmed by the varieties of different pistons.

I would like to have the same or slightly higher compression.
But I don't know whats the stock CR.
I read somewhere between 8.5 and 9.5
But if i try to calculate the CR I get 10.5

Bore 4"=101.6mm, Lift 3"=76.2mm -> 617.78cc per Cyl
Combustion Chamber Volume= 65cc (average)
CR= (Displacement of one cyl + cc-volume) / cc-volume

I always thought the octane measurements were the same in Europe and US, but I'm wrong.
Here in Germany the lowest octane fuel is 95, but it's equal to US 90 octane
So I could get higher in compression for 90 octane, but I don't know how high I can go until I have to use 98(E) / 93(US)

I hope I can gain a few HP and better mileage by using lighter material.
The Motor will not get raped by using a blower or nitrous, so I thought Hypereuretic Pistons might be a good choice.

Sooner or later I want ot install aluminum Heads.
Preferably Ford Racing Turbo Swirl, but I haven't decided if 64cc or 58cc

So I don't know what pistons might be the right choice for me.

 

I make it simpler:

Is this a good kit for a street rebuild with a CompCam 35-512-8 (.480 Lift), 1.6 Rockers and Stock heads and optional FMS-M-6049-X306 Heads?

http://www.summitracing.com/dom/part...-300/overview/

Or do I get in trouble with the missing valve reliefs?

 

What heads and cam are you running ? The stock roller block 302 pistons had a pin height of around 1.615-1.619 these will give you a near zero deck clearance and the most compression. With the stock 64 cc chambered heads, the comp ratio is about 9-9.5 to 1. The pistons without valve reliefs will not work with those heads and cam. They're replacements for the 86 HO 5.0 and the 86-91 Crown Vic 5.0 these engines had different heads with the valves located a full 1/8" deeper into the heads, thus they did not need valve reliefs.

 

The Cam I'm running is the Comp Cam 35-12-8 (Roller).

I want to use the stock heads (didn't check the casting number but it's pre'93) for now ans I want to change to Ford Racing Heads when I can afford them.

 

You'll need pistons with valve reliefs to run either head.

 

Allright.

I took one piston out and measured it as far as I could.
- Bore: 4.030
- Stroke: 3.00
- Rod length: 5.09
- Pin Diameter: 0.9, press fit

The only thing I could not find out is the compression height, because my sliding caliper is too vague.

The height is somewhere between 1.6 and 1.62

That narrowed it down, but now the question is "Flat Top" or "Dish" ?

 

Measure from the top of the piston to the top of the pin bore. Then measure the pin bore. divide the pin bore diameter by two and add that to the distance from the top of the hole to the piston top. That will give you the pin height. For the most compression you'd want flat tops, but most 302 pistons have a slight dish. So you may have to choose between those combined with the tallest pin height (also called compression height or distance)

 

I did, but I only have a metric sliding caliper and it says around 33.5mm from top of the bore to the top of the piston.

Therefore I borought the digital sliding caliper from my Father, which is switchable between Metric and Imperial.
The Height is 1.32 (+0.3 bore radius)

 

That figure of 1.32 has got to be off. That added to half the pi diameter (.912/2 = .456) equals 1.776 . The pistons would be sticking above the bore by an eighth inch or more.

 

http://www.summitracing.com/parts/sl...view/make/ford

Maybe these.

http://www.summitracing.com/parts/pb...view/make/ford

Or these.

 

Not necessarily - the rod is still connected to the piston, so I measured from the inside of the pin
The inside diameter of the pin is 0.6


The Probe pistons have only two reliefs.
Therefore comes two more questions in mind:

- Contains this kit 4 pistons for each direction?
The pin bore is usually not in the center of the piston, so therefore there's an install direction.

- Do the 2 "missing" valve releases cause less unwanted turbulences within the detonation?

 

OK, then you're going off the inside of the pin. Some pistons have offset pin bores, some do not. Any piston kit will have the correct number of pistons for each bank, or should have. If not then they'd be mis-packaged. A for the two fewer valve reliefs, that would theoretically yield a higher comp ratio. As for turbulence, that's something you would want to improve fuel/air mixing. And the flat part of the piston without the reliefs would add a bit more "squish" to quench any unwanted detonation as long as the pin height puts it as close to the bottom of the head as possible. 302 pistons come in such a wide range of pin heights, that's what you've got to look out for, this ranges from 1.585" to 1.620", that .035" difference equals about 9cc's in volume in the equation when figuring the ratio. And with a small displacement engine like this, 9cc's adds up quick in the difference. This is why I tell everyone shopping for 302 pistons to pay close attention to the pin heights, not all "flat top" 302 pistons are the same.

 

RSR Static Compression Ratio Calculator

 

Inlet Runner and Peak Torque Calculator