[Gulf00]

I did some calculating on the compression increase I would get when I bolt my 66 289 2V heads on the 302 block I'm planning to swap the 289 block for.
If I did that right, the compression would be 12.5:1. No I was wondering if I can run a compression like that without getting into trouble. And if not, what is the best way to go, increase chamber size somehow, or go with reinforced components in the block (I figure the latter to be quite expensive). And how is the best/easiest way to decrease compression (I calculated when I do it by getting a thicker gasket I'd need a half inch thick gasket...).
Anyone experienced with this? The 302 block would be rebuilt and checked for cracks and all that.

Thanks,
Matthijs

 

[Paul G.]

compression

Gulf00,
I don't know what type of gasoline you plan on running, but 12.5 is high for pump gas. I would consider dished pistons. There are a zillion different pistons available for the 302. A dished piston will lower compression. What type of duration figures are you planning in your cam. A big duration/overlap cam can help with cylinder pressure to a degree, but I still think a good forged dish piston will allow you to create any compression ratio you want.
Paul G.
69 XR7 Convertible

 

[swamper]

If this is for street use, I would definately drop compression. When rebuilding bottom end, look at dished pistons as an option to get it done.

Maybe you have much better gas than we do though!

 

[Gulf00]

Well, thanks in the first place. I'm planning on a [email protected]" cam and need the car for street use (not many tracks around here...).
The premium fuel here is 98 octane.
I must say, piston changes are not the answer I was hoping for, since I was not planning on taking the cylinder block apart myself for I just don't have room or tools to do that (now the tools I can overcome, but to get around the car in the garage requires a fair amount of squeezing).
But maybe I can arrange something with the guys who're gonna rebuild the heads.
So next question: What would be the max compression ratio I can run with the cam mentioned and the 98 fuel?
And, when to consider the rigidity of pushrods and other components. I'm trying to get the little motor as close to 400 bhp as I can.

Thanks,
Matthijs

 

[greggieatthebat]

98????? (greggieatthebat has curled up into a jealous little ball sitting in the corner)

 

[72cat]

What do you guys get in USA, we get a choice of 97 premium or 95 unleaded, if any petrol attendant dares to ask whether to put 95 or 97 in my cougar I am going to deck him.

 

[greggieatthebat]

Usually 87 (Regular), 89 (Plus), or 92(Premium/Supreme). Premium for some brands is 91, Union76 has a 93... Union76 is also the only one that I know of that sells 100 at the pump (hard to find, though, and $$$).

 

[72cat]

So, in going back to my post re miles per gallon, is 12 miles per gallon good or bad when I am using 97 premium.

 

[Gulf00]

98????? (greggieatthebat has curled up into a jealous little ball sitting in the corner)

What you pay is what you get right? Regular (95) costs EUR 1.149 per litre ($4.30 per gallon)
Premium (98) costs ya EUR 1.20 per litre ($4.49 per gallon).
So you might have figured it already, the cougar is meant for pleasure purposes only...


But, what about the comp ratio question?


Cheers,
Matthijs

 

[Royce Peterson]

Matthjis,

I can't imagine how the compression would be that high if using the original pistons with 66 289 heads. Are you certain you are calculating the compression correctly? Those heads are typically around 60 - 65CC combustion chamber. That would yield something like 10 to one depending upon the head gasket thickness and how far below the deck the pistons are at TDC. Typically in 302's the piston is .040" down at TDC giving even lower calculated compression.

I would think 10.5 to one is safe with the excellent gasoline available to you.

 

[72cat]

Our 97 would cost $1.46 per gallon, $0.38c per litre.

 

[swamper]

South Africa gas sounds good. $1.62 Gal for 92 Octain here. One specialty place in Spokane had 110 Octain for About $5.00 gal.

 

[72cat]

110 - wow, guess if you had the bucks it would be worth it.

 

[Cougrrcj]

Not all octane measurements are the same! Here in the US, they use an average of the Pump Octane and Research Octane for our cars. They two octane measurements are resolved by using two entirely different testing methods. Don't ask me how they differ, but trust me, they do! I strongly suspect that those high octane numbers our foreign board members are using is just the straight number of the high testing method.

OK, case in point. In aviation they actually show both octane numbers on the pump. Most of your average light aircraft engines were designed with low octane gas in mind. There used to be an avgas with a rating of 76/80. Then there was a higher rated fuel at 94/100 and now there is what they call 100LL (for Low Lead). The ratings for the avgas they used in the highly supercharged piston engines of WW2 aircraft was a 110/130 or 115/145. Each grade of Avgas is dyed a specific color to an international standard so as to avoid confusion. Back when I was flying 25 years ago, our club Cessna 150 used the 80 octane gas. A few years back the petroleum companies started phasing out the 80 and 94 because of the small niche market. Now almost all are 100LL. That created a bunch of problems using the higher grade fuels in the older engines (too much lead causing fouling, etc.). Many light a/c are better off running autofuel, and do so! It is cheaper and generally has less anti-knock additives that cause the problems in old-tech aero engines. There are drawbacks to this, however. Blah, blah, blah, blah, BLAH!

Enough of this tech-talk!

Our racing fuel we can buy for our 'off-road only' race cars is usually available in either a leaded or unleaded variety. Most are blends of various combustable fuels. Some are even almost straight paint thinner (toluene)! I can go buy racing fuel at the local gas station for $3.49/gal for 108 Octane unleaded.