Which headers?! 71 F100, 302, 3 on the tree

[ScreaminZ]

Assuming the numbers you mentioned above were correct, it sounds like the thicker one would better for a street driven vehicle. 9.5:1 works very well on most pump gas, at least around here. I don't know what your gas is rated at over there in Germany. The higher compression ratio with the thinner gasket will give you more power and torque, but is right around the limit for most pump gas. You will likely have to buy premium gas to prevent detonation. Again, this is assuming the gas you buy over there is similar to what we have here in the States.

[Florian]

Regular gas has got 95 to 98 octane. Premium gas has got 100. Is that the same as in the states?

[ScreaminZ]

Wow, you've got it GOOD!! Regular unleaded around here is like 87 octane. Premium is 92 or 93. Sounds to me like you'd be just fine with either head gasket.

[Florian]

Really? I wouldn´t have expected that!

Well, then I´ll take the thinner gaskets

Thanks for your help, ScreaminZ!

[ScreaminZ]

A quick read on Wikipedia ( http://en.wikipedia.org/wiki/Octane_rating ) shows that octane is measured a little different over there and your 95 octane is roughly equivalent to our 91. So it's not as big of a difference as it first seemed, but still enough to help you out a lot.

[Florian]

Ah I see I talked about RON and you meant AKI.

So around 91 AKI is still fine with the higher compression ratio?

[Dragon]

My truck and my Volvo both require Premium. The truck is factory 10.25 to one and the Volvo is 9.91 before Boost with 12 to 1 on boost. They both run fin with Us 91 and they both suck on regular. You can feel the difference. I would not care if they had lower requirements. When work is slow Premium in every tank is painful.

[ScreaminZ]

Ah I see I talked about RON and you meant AKI.

So around 91 AKI is still fine with the higher compression ratio?

It's hard to say exactly what your engine's going to want. There are a lot of variables involved in finding out what the dynamic compression ratio is. You will more than likely be just fine with the higher compression ratio. If for some reason it doesn't like it, you can step up to the next grade and be just fine. It would be a good idea to double-check your numbers before you decide for sure which gaskets you're going to run. You don't want to get it all together to find out that you ended up at 12:1 and have to run the most expensive gas you can get!

[Florian]

You don't want to get it all together to find out that you ended up at 12:1 and have to run the most expensive gas you can get!

That´s exactly it.

Is it possible to determine the deck clearance before assembly? I know all the other variables. I could measure my new pistons and rods, if I then knew the stock deck clearance I could calculate it. Or I can compare the old pistons and rods with the new ones, the difference in length should then be the same difference on the deck clearance.

[Dragon]

The rod length center to center with the piston attached, center of the wrist pin to the flat deck . Then the crank at TDC equals the installed height. The Crank centerline to the top of the deck is the true deck height. Subtract rod, piston and 1/2 the stroke from the deck height and you have the deck clearance. If the deck top has been milled then the true deck height has to be measured not the book number.

Some pistons list their deck installed height as part of the spec. .010 difference can make 1 to 2 compression points difference.

[Florian]

I measured one assembled rod and piston. It´s 6.57" from top of the piston to the center of the rod.

The deck height on a ´71 302 is 8.206" - 1.625" (half of the stroke) - 6.57" = 0.00879" deck clearance.

Here are my numbers now:

Bore 4.030"
Stroke: 3.25"

Combustion Chamber Volume 60.00cc
Piston Head Volume 11.00cc

Gasket thickness: 0.0??"
Gasket bore diameter: 4.0??"


I tried it with a 0.040" thick gasket and a 4.080" gasket bore. That would give me 9.34 : 1 static compression

The gasket is the only variable now.

I tried different combinations of thicknesses and bores and found the highest CR with a 4.100" 0.038" gasket. It makes 9.38 : 1 But other gasket sizes vary only 1 per cent less..There is a 4.060" with 0.021" but it´s machined for o-ring..


Isn´t 9.38 : 1 a bit low? That is even below stock compression I know I haven´t got an alternative, since I don´t want to buy other pistons...and a 58cc head won´t change that much either..

Alternative gasket sizes would be:

4.080" - 0.039" @ 9.37 : 1
4.100" - 0.039" @ 9.36 : 1
4.060" - 0.040" @ 9.35 : 1

Which size would you recommend me and why? Is there that much of a difference between these sizes or is it pretty much the same?

Thanks!

Florian

[Dragon]

That is not low I built an FE with 7.25 to 1 and went 140 with it in a 68 F100.

[Florian]

Really? I thought it was kind low because I read somewhere that the stock 302 had 9.5:1

Thanks for your fast reply!!

Good night

Florian

[Dragon]

My Volvo is 9.91 before boost and runs regular with no problems. If I let the Turbo come online I have to have premium as boost allows me to hit 13 to 1. You are talking static compressions When the cam, intake, carb, headers and head porting all come together the engine will have a much higher compression ratio.

[Florian]

Okay then it´s alright. Thanks!!


I just placed my order at Summit and it seems that the Edelbrock cylinder heads I chose are not available before end of October. However there is almost a similar set of heads that is the same as the one I wanted, only it has an intake valve diameter of 1.900" instead of 2.020"

What are the benefits of a larger intake valve? Or would the 1.900" valve also be ok for my application?

Florian