Did someone throw a boat anchor behind my car at 4500?

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max71
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Joined: Sat Jun 02, 2007 9:36 am

Re: Did someone throw a boat anchor behind my car at 4500?

Post by max71 »

Not to beat this to death (too late :lol: ) but here's what Sean Brown wrote to me:

There was absolutely nothing unusual about the head or intake manifold that would indicate this problem and I have never had anyone have any trouble with this that I am aware of.
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max71
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Posts: 422
Joined: Sat Jun 02, 2007 9:36 am

Re: Did someone throw a boat anchor behind my car at 4500?

Post by max71 »

Had a long talk with Phil at APT and got some more headway on understanding what's going on.

He said the VP-11 is rated to 10:1 and above that they recommend the VP-12

I went through my notes and found this which means it isn't as high as original numbers thrown around. I forgot the numbers were revised by a friend who was doing the math once I provided specific specs.

Good news!

If you use a single standard head gasket it looks like you will be dead on
to where you want to be, almost exactly 9.5 to 1, actually it will be
9.489141415186274 to 1. I didn't figure that you needed to take it out to
the 16th decimal place so I stopped at 15. LOL

With this ratio and the Weslake combustion chamber shape you will be able to
burn 87 to
89 octane gasoline.

Data used:

Bore: 3.19 ( 0.030 over standard )

Stroke: 3.5

Head gasket opening diameter: 3.25 (guesstimate on yours as I measured a
compressed gasket that I had around here)

Compressed head gasket thickness: 0.021 (ditto on the gasket that I had in
the shop)

Chamber volume in CCs: 42.6

Piston dish volume: 6.5 CC

Deck clearance: 0.016 (guesstimate but a little variation won't affect
the CR very much)


So it looks like I should be in the range for the VP-11. Phil seems to think based on a similar problem he had in the past with a race car doing the same thing that getting one thousand jets and appropriate needles might solve it. My compression is fairly high 194 per cylinder with one at 200.

I'm happy the Coopers fixed it even if its a bandaid. He said he has the bits in from his toolbox that he'll send me to test out to see if it fixes it. Like Malcolm he believes I am leaving performance on the floor but going back to Coopers. At least there's headway and if the jets don't fix it I'll just leave it alone with Cooper. Rather have drivability than every last bit of performance at this point.
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