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MG TD TF 1500 - Supercharger Question

I recently finished the rebuild of my Judson supercharger. I got parts and lots of advice from George Folchi. I've got a few hundred miles on it now and the car is running well.
I am a little concerned by the lack of boost pressure. When cruising locally at anywhere from 45 to 60 mph and I stomp on the gas I can only get a little over 2 pounds of boost. I thought it should be more like 5 or 6 pounds.
I thought it might be my old gauge but I hooked up a new one and got the same thing.
Any suggestions would be most appreciated.
Thanks,
Mort
Mort (50 TD "Mobius")

Mort, I believe that in order to obtain more pressure, the blower must be geared for higher RPM. This means different diameter pulleys on either the crankshaft or the blower or maybe for both.
Jim Merz

You should hit the throttle and be at about 6 lbs boost. when running there should be little or none. Mine would be hitting 6 or more when you stomped on it. Are you sure you are tight at the supercharger on your line from the gauge?
Tom Maine (TD8105)

It's going to depend on the engine rpm and at what rpm it takes for the blower to make full pressure. If for example your were running at say 2000 rpm when you mashed the throttle, the the odds are the blower isn't yet at it's optimum capacity. On the other hand if you were say at 4000 and gave it a stomp then I would think you would see just about all your going to get. I'm just guessing as I don't know the particulars of the Judson operation.
LaVerne

well, 45 to 60 is definately past 2k RPMs. Either the pulleys are way off, belt is slipping, or the lobe clearance in the blower is to excessive and just not able to build boost. Or if you have a blow off for excessive pressure, it might be popping to early.
L Rutt

If you are talking to George F, I would ask him. Or, Dominic Clancy on the MGA board has a lot of info re Judson available, and I believe he has it all posted on his website.

FRM
FR Millmore

well, 45 to 60 is definately past 2k RPMs. Either the pulleys are way off, belt is slipping, or the lobe clearance in the blower is to excessive and just not able to build boost. Or if you have a blow off for excessive pressure, it might be popping to early.

Not exactly true . I believe he has both a 5 speed and a 4.3 rear end.
LaVerne

LaVerne you have an excellent memory.
I put in the Skyhook 5 speed about a year and a half ago.
It is probably a 4.3 rear end but I do not know how to verify.
Can someone clue me in?
Thanks,
Mort
Mort (50 TD "Mobius")

Mort,
I'd put a mark at the bottom of the tire, and a mark on the driveshaft- ease the car forward or back by hand and count the revolutions of the criveshaft with one complete revolution of the tire.
This isn't precision, but you'll know close enough whether it is the 5.12, or 4.3 (or what else?).

Concerning your blower- if the engine is much larger than the displacement the supercharger was intended, the boost won't get up there without redoing pulley ratios.
Jim Northrup

My Judson comes on strong right at about 4000 - anything less and it's off the cam and off boost. So when you want to get around something (sort of) quickly, you throw the shifter into 3rd, buzz the little bugger to 6000, and then the Judson comes on nicely.

Dave
Dave Jorgensen

This is an interesting article on the Worlds Most Powerful MGB with an MGB engine.
Mike

http://www.concourscars.com/uploads/pdfs/MGB.pdf

Mike TD/TA

Curious article. Much BS, factual errors, lame "British" comments, flailing around. Power is good for a street car, but there are NA MGB with near that power; I reckon the blower ought to put them well past this.

Glad I'm not paying for them to rebuild any of that list of cars at the bottom.

But they got good stickers on the fenders.

FRM
FR Millmore

Mort,

To determine the ratio of your rear axle, jack up ONE rear wheel, get a helper to count the revolutions of the drive shaft while you rotate the lifted wheel 20 turns.
divide the result of the drive shaft turns by 10, that will give you the ratio.

for example 51.25 drive shaft revs = 5.125
43.00 drive shaft revs = 4.3

John



J Scragg

Mort,
I have a fair bit of experience with turbochargers, but not so much with supercharges.
I had a customer for years who had a beautiful BRG mkII with a Judson supercharger. I would do the annual maintenance on the car, and it was a blast to drive. That supercharger would really kick you in the pants.
To me, it sounds like you may have a leak, or your "release valve" is adjusted to blow too early. I do not know what it is called on a supercharger. On a turbocharger, there is a waste gate that dumps excess boost pressure.
I would look for a leak, and check the release valve. It sounds like your boost pressure is being vented off after 2lbs of boost.
-David
D. Sander

Dave S,
As far as I know (and I've completely disassembled it and rebuilt it) the Judson supercharger has no waste gate/release valve.

Dave J,
I'll have to take it out on the turnpike one day soon. There is no where else I can get to those RPM's around here. The turnpike entrance is only about 2 miles from me. I just have to pick a low traffic time. Perhaps Sunday morning.

Jim Northrup and John Scragg,
Your two methods seem off by a factor of 2 from each other.

20 turns of the wheel gives me about 48 turns of the drive shaft????? 4.8 rear?? 2.4 rear??

Propane around all the intake points(gaskets, fittings etc.) shows no change in idle. Propane at the carb air filter kills the engine.

Mort
Mort (50 TD "Mobius")

Dave J.
My RPM's are lower because of the 5 speed transmission.
Mort
Mort (50 TD "Mobius")

Mort, it's that thing called the differential that's making the difference. Notice that John's technique has one wheel fixed, i.e., on the ground. Jim's allows both wheels to spin. There are those among us who can use the proper terms to describe this action of the spider gear, but I'm not one. Try it out.

BTW, Mort, have you considered using a lower gear to get the higher rpm at a lower speed? Bud
Bud Krueger

Stop laughing!
I counted the rotation of both the wheel and the drive shaft myself.
This time I got my wife to rotate the tire and I counted the drive shaft.
It's a 5.125 rear end.
Mort (50 TD "Mobius")

Re: World's Most Powerful MGB
PSE Supercharging- "Rootes type of supercharger
is not designed to be run wet (having
fuel pass through it)."
Must've talked to the receptionist.
Then to build a fuel injection system on that advice!

Mort,
Glad you sorted out your rear ratio.

Are you running a 1250cc XPAG, compared to say, a 1466cc XPEG or an 1798cc MGB? (The Judson could actually choke the B engine down in power with no boost, so that's thrown in just for the extreme.)

JIM
Jim Northrup

Jim,
The engine is original to the car.
Car TD/1851
Engine XPAG/TD/LHX/1606
Reasonably close to 1250cc
And I'm much better off now that my rear end is sorted out.
Mort
Mort (50 TD "Mobius")

Mort - your car would be much nicer to drive if you put a 4.3 diff into it - there are plenty around.

Tom Lange
MGT Repair
t lange

Tom,
I was concerned about overdoing it. With the 5 speed Skyhook transmission it cruises very nicely.
I just do local driving and sometimes on a highway to get to a show or event.
What would the 4.3 do for me in practical terms.
Thanks,
Mort
Mort (50 TD "Mobius")

Mort,

I have the Skyhook, 4.3 rear and T. Lange blower (Eaton type) and except for a flat spot under load at about 3k RPM the whole setup runs very nicely. I hope to cure the flat spot when I have the dizzy recurved this winter. On the highway I do 60mph at 3k RPM.

Regards,
Jim
James Neel

Jim,
How is the performance at lower speeds? I was concerned about driving in traffic and in areas with lower speed limits, such as back roads and towns.
Thanks,
Mort
Mort (50 TD "Mobius")

Mort,

That's the beauty of the setup, it works great with the 5-speed tranny, fourth gear for local and back roads and 5th for the highway. I have punch through the entire rpm range except for that flat spot I mentioned which is only under load and I can downshift to avoid that under most circumstances.

Jim
James Neel

OK Gentlemen,
Since I need some new projects to tinker with I will put this on my list for this winter.
Any advise would be appreciated.
Where to purchase?
What other parts will I need?
The best source for instructions?
TIA,
Mort
Mort (50 TD "Mobius")

I'll throw my two cents in here for what it's worth. I put the 4.3 rear end in the TF a month ago. I've been running the Skyhook 5 speed for several years. I also changed the Eaton blower pulley this winter and had Jeff recurve the dizzy and now make almost 10 lbs of boost. After driving about a 1000 miles a couple of weeks ago during the Glenwood Springs Rallye I wish I had left the stock 4.875 in it. The car was much quicker before. I'd have put it back in already but I put that rear end in the TD. So I'll have to pull the one out of the TD and put the 5.125 back in it and then swap the TF rear and then put the 4.3 in the TD...I think. I'm not going top do it on the ground and only have one lift in the shop.

Before the blower with the 5 speed I got 31.5 miles per gallon.

With the blower addition running 6 lbs of boost it dropped to 22 mpg.

On this latest trip that dropped to around 16 mpg. Probably more because of the pulley change but with the rear end change I find I'm almost always pulling some boost. Wish I had done a check before the rear end swap.
LaVerne

Mort, see http://www.ttalk.info/ClarkConversion.html for info on Dave Clark's work. Bud
Bud Krueger

This thread was discussed between 25/06/2012 and 03/07/2012

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