Rear gear selection - Page 2

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  1. #16


    Attached are cam specs, and the dyno sheet.
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    As I said, I’ve been steadily increasing launch rpm by the end of last year, it may very well have more in it that I didn’t get a chance to see due to the end of the season.

    I do know according to the go-pro when I’m at 4k about to launch, I’ve built 10psi on the transbrake.

    One thing to keep in mind was that was I found out I had low compression in about 6 cylinders. So, was I down on power? Probably so. At least a bit.

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  3. #17


    Here’s a better dyno picture...Name:  945B709B-2536-4637-BF20-0AD0EB4EB5CC_1590174157249.jpg
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  4. #18


    You might want to check out where the cams were actually installed, Matt.

    In one location, the cam card indicates the cams are installed straight up (0˚ Adv/Ret) which would imply a 2˚ overlap as illustrated by Mark Olson's CamChart S/W below;

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    More towards the top of the cam card, the card indicates the cams are ground on a 114˚ C/L for the intake and a 122˚ C/L for the exhaust which would be a 118˚ LSA advanced 4˚. That would look like the image below;

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    Of course neither of these two different phasing may be what the cams actually are or are installed at. It is possible they are different and were installed with a third phasing that was yet different than either of those above.

    I am beginning to think it might be a good thing to check them out just to know what they really are and where they really are installed at. BTW they certainly are not shrinking violets in the valve lift department.

    Last edited by eschaider; 05-22-2020 at 02:54 PM. Reason: Spelling and Grammar

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  6. #19


    Ed, I installed them with the comp cams adjustable gears you recommended. And I installed them with dial indicator on valves, I believe you were holding my hand the whole time 😂

    If you would like I can go back through that thread and my notes and pictures and get the numbers.

  7. #20

    Somewhere around post 145.

    To jog the memory, I set both banks at the 114 ICL which I found out was 11 degrees off if I were to have just installed dot to dot. Basically one bank was advanced and the other retarded to meet that ICL

  8. #21


    I went back and re-read your post (here is the link=> I had forgotten that you did the phasing and you documented it. You are correct the cams are at 114.

    When you describe cam phasing use the advance and retard representations as modifiers to the actual cam phasing. For example if the cam is cut on 114˚*centers as yours are, then installing them at 114 is putting them in straight up. If you install them at 112 and 116 then you have advanced the cam(s) 2˚. To get that 2˚ advance may require an offset at the cam of a different number like 4˚, 6˚, 8˚. That offset is typically compensating for one of two things.

    • The first. is a predisposition of some cam grinders to build a small advance into the cam for low speed performance. They know most of the cams will end up in street vehicles and poor bottom end is a kiss of death for the cam manufacturer follow on sales.

    • The second, is just a sloppy core supplier that did not get the cam keyway precisely at or near the zero point. Cam cores have additional material on the raw lobes which the cam grinder removes more or les of for a particular cam profile. If the core supplier is far enough off the mark then the finished goods cam can be a few dereees off of where you might expect it to be with the chains and dots "lined up".

    Another potential whoops you want to be attentive to, as the engine builder (particularly on the 4V engines), is the fit of the exhaust cams in the heads. Some core suppliers will provide the exhaust cams with five ten thousandths (one half thousandth) additional on the cam journals. I have never gotten a good explanation of why. When you install the cams in the heads the intakes spin effortlessly. The exhausts have a very noticeable drag associated with rotating them. The drag is the additional five, ten thousandths of an inch diameter on the journals. Most of the time not a problem but then there is always the one time it is a problem. In my experience it has only been a problem when I build the engine. Everyone else seems to get a pass on the problem.

    Matt's engine is already built so the next comments are for everyone else who later reads this thread. The last thing to get oiled in an OHC engine is the cams. That means during the build cycle the last thing you do as you assemble the cams to the heads is to add a single drop of ProLong (<= clickable) to each cam saddle and cam cap to provide lubrication at cold start before the oil system can deliver lube to the journals. Then always run ProLong in the oil to protect the top of the engine when you garage the car for a week or more because the lube will run out of the space between the cm journals and the cam saddles asking the cm to scuff the saddles.

    Parting thoughts on the Prolong. A 12oz bottle costs somewhere between $15 and $20. The gallon bottle on the clickable link above costs $64 and has 128 oz of ProLOng in the bottle. Do the math — its way less expensive to by the gallon bottle.

  9. #22


    I also like to pre-lube using the Peterson pump a few minutes prior to starting.

    As Kevin stated it’s simply not leaving in a hurry. That may be because it was getting low on power (low compression) or there simply wasn’t enough launch rpm.

    Because the 60’ is done solely in first gear I want to focus on it more than the 1-2 shift.

  10. #23


    The Peterson remote with the built in lube pump is excellent for preluding an engine that has set for a while prior to starting it.


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