Hopefully, the following will help you in determining how much you want to
shave off your head. From the Competition Prep. Manual: Compression 8.5:1 -
Head thickness = 3.460", Compression 10.25:1 - Head Thickness 3.375". After
taking off the head measure the head, more than likely you a head thickness
of 3.550 " (make sure that you have a 74 head on your car, in my case on my
73, I had a later head). In my case, I had 0.145" shaved of the head for a
9.5:1 compression.
Plot the compression vs thickness and estimate what it will take to get you
to the desired compression. If you research the VTR site, you might get
some experiences from others as to what they had shaved to get their desired
cpmression. This research may also get you some other points on your graph.
Also, you might consider (after taking off the head) is to measure the head,
measure the length of each of the push rods (they will all be a little
different), ask BPNW for the length of their short rods, and then determine
how much you want to shave off your head. In my case, that is what I did
and with differences in the orig push rods and the short push was about
plus/minus 0.0145 inches.
If you need other information please let me know, I did my head last summer.
Martin
>
>I've got the head off my '74 TR6 as part of the camshaft replacement.
>Since it's off anyway, I'd like to up the compression a little bit. I
>understand the '74 and up engines had 7.75:1 compression ratio.
>
>I'm considering asking the machine shop to take off 0.040". Am I correct in
>assuming this would take it to somewhere around 9:1, and that I'll still be
>able to use the stock pushrods? I don't have a competition prep manual, so
>I'm pretty much shooting in the dark.
>
>The head has never been off before. I've fitted a BL S2 (fast road) cam
>grind.
>---
>Ted Stevens stevens@erols.com
>74 TR6 Gaithersburg, MD
>
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