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TR4/4A TR4A IRS-SC?!?!?!

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Hi Scott,

I get 20 or 30 psi of vacuum at idle. It does get to 0 with full throttle.

I did some experiments with my MightyVac. I found that the bypass was stuck open from my last drive. I pushed it and it snapped back shut. I wasn't able to reproduce getting it stuck open with the MightyVac, but it doesn't close smoothly, either. One guy at Moss disables his just as a matter of principle. The down side is potentially lower fuel economy, and a little more wear on the blower bearings (they always turn, but not under much load when bypassed).

I can't tell were the mechanism is hanging up, either in the linkage, the butterfly or in the vacuum cylinder.

I'm going to do some tests with the bypass disabled.

I was thinking maybe I would add a manual control of the bypass, and use it long long trips, and when the kids want to use the car :smile:.
 
Hi Darrel Not sure if you posted this but I'm curious to know what modifications you did to your cylinder head if any? What is the compression....8:1...9:1 ? Stock pistons. stock crank, Stock cam??? What is the boost you are using... 5 psi? thx Karl
 
Hi Karl,

I have the aluminum head from Moss, I didn't make any mods to it. I'm using a 0.032" solid copper head gasket (I'm told the stock head gasket is ~0.060 compressed), and I have 87.5 mm pistons. Assuming the combustion chambers on the new head are the same as stock (I didn't measure them), I calculate my C/R is around 9.3 or so. The guys at Moss say there shouldn't be any problems until the C/R gets over 9.5.

I have a mildly upgraded cam from BPNW (270 degree), and I'm running the 4-2-1 header into a stock single-muffler system. The crank is stock (balanced, everything was when I rebuilt it a few years ago). I think that is all the engine mods that are relevant.

I'm showing just under 5 psi of boost. I do have a smaller blower pulley, that should give me another pound or so, if I decide to put it on.

-Darrell
 
Thanks Darrell. A friend of mine is building a TR3 motor using a Judson Supercharger so I'm watching your progress with interest. Karl
 
Hi Darrell,

Sounds like you have found the culprit. Can you remove that rod between the actuator and bypass valve, and then repeat your test with the Mityvac? You could also then manipulate the bypass valve by hand -- that should give a better idea of exactly where the problem is. Hopefully Moss is not suggesting that you disable the actuator -- you have done a lot of work for them and I would think that it would be in their interest to get your sc kit working properly, toot sweet.

As an aside, I know those boost gauges are not extremely accurate (or easy to read), but 20" is more vacuum than I would expect from an engine set up like yours. Might want to get a diagnostic gauge and a) find out what the actual vacuum is at idle and 2) retard your timing so that vacuum is around 17" at idle (if it is greater than that). As you probably know, too much timing advance can be especially detrimental on high compression and/or forced induction engines. As a further aside, if you are going to add the smaller pulley for more boost, you may want to look into an ignition system with a boost timing control function, such as the MSD 6-BTM, to guard against detonation under boost.

Scott
 
Hi Scott,

Disconnecting the actuator is just a diagnostic step, though the downside of keeping it disconnect all the time seems minimal. Unfortunately, the arm on the actuator is isn't easily removable from the bellcrank that operates the bypass butterfly (and it doesn't help that this is all on the bottom of the blower).

I could be a bit off on my idle vacuum numbers, I mounted the gauge in the center console where a radio would go, so it isn't right in my line of sight, and my key fob hangs in front of it. And it covers 50 psi in about 270 degrees of sweep (-30 to +20), so it could easily have been around 15 psi.

I do need to check my timing more carefully, the specs I set it up to for the Webers match what is recommended, but I need to verify it.

-Darrell
 
Didn't have time to drive today, but did warm it up and check the vacuum at idle. It looks like 18" of mercury (I also noticed, with closer inspection, that the gauge is inches of mercury on the vacuum side, and psi on the boost side).
 
What a great thread on a beautiful car Darrell!

I know the up front cost of a blower is chunky but man, what a great way to have get the kick without the hysterics of multicarb/ high compression /hot cam set ups.

I gotta get me one of them!!

Cheers,

Doug
 
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