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MG TD TF 1500 - XPEG H4 SU needles on the Dyno

On a dynamometer of a 1466 TF when finally dialed in, with AN needles, produced 91 HP & 80 F/P of torque @ 2500, 96 F/P @ 3600 & 90 F/P @ 5300 RPM. A Laystall head & Abingdon Performance Ltd. Roller cam kit were the only modifications, otherwise Completely STOCK.
I hope this information helps others with H4 carbs!
(OEM needles are GJ).
Len Fanelli

Excellent HP! Interesting: it seems telling that the needle you settled on, the AN needle, is significantly leaner all across the board than the standard GJ.

Tom Lange
MGT Repair
t lange

Thats nice....what was the reading before you made the changes? And at what altitude? At the flywheel I'm guessing?
L E D LaVerne

My 1250 always ran rich. I noted in the Octagon magazine that dropping the needles in the piston was the equivalent of weaker needles. I did this and after a bit of trial and error the TF's engine is running superbly.

Jan T
J Targosz

The power is good, but since the head and camshaft are where most of the power comes from, maybe saying "otherwise stock" is a bit misleading. To buy a Laystall head, roller camshaft, plus everything necessary to get it installed and working (uprated fasteners, etc), that's close to $4,000 USD and you still have to rebuild the rest of the engine. So the owner of the engine about probably has at least $6K into the rebuild, and probably another $1K into head machining to get it to breath like that.

I have a roller cam in my TC and I'm about to put a rather expensive head on it (modified original) but even with the compression bumped to 9.2 I'm not expecting 90+HP. So I have to wonder what else was done to the above engine that wasn't mentioned, like compression ratio, advance curves, valve sizes, headers, etc. If I get 90HP then I'll be thrilled of course!
Steve Simmons


I don't want to disparage Len. I hope some day to get a roller lifter/cam kit.
I generally believe his data but I have an issue.

Len said that he measure 91 HP at 2500 rpm. But HP is a function of RPM.
Generally over a wide range of rpm Torque is relatively constant.
now ((Ft-Lb)#rpm)/5252 = HP. I I calculate this for Len's 90 Ft-Lb @ 5300 rpm we get just about 91 HP.
However the 91 HP at 2500 RPM is not possible.

There must be a mis-typo here.

Jim B.
JA Benjamin

Len sent me a copy of the dyne sheet its 91hp at 5500rpm, and about 39hp at 2500rpm.

Bernie
B W Wood

Huffaker Engineering did the engine building and dialed it in on the Dyno, at sea level.My customer bought the head previously & it was left untouched, 9:1 C/R not milled, no port work done,stock XPEG valves.A normally aspirated XPAG with a street roller cam will not produce 90 HP.An XPAG head with the larger valves,ported and both valves un shrouded will flow as good as a stock Laystall head IMO.Use an old head gasket as a template for un shrouding both valves.
Manley Ford has the best custom head gaskets, and his extractor manifold works very well.
Len


Len Fanelli

I have now found out how they were able to use this leaner needle from the customer: "I do know that Huffaker does not keep oil in the top of the carburetor because they like the piston to move up without a lot of damping or resistance. I only mention this because it is different from what most guys say about SUs".
Len Fanelli

Maybe just for the final tuning process, othewise it makes no sense.
Dave H
Dave Hill

Removing the oil from the dashpots would only make a difference during the brief moment there is a change in throttle. It would cause the mixture to lean out a bit until things stabilized. Unless I'm missing something, I can't see how removing the damping oil would affect needle selection. I know racers sometimes run thin oil or no oil for a quicker response, but that's on engines that are being run mostly WOT.
Steve Simmons

Len,

Do you know what colour spring they were using in the dashpots?

Bernie
B W Wood

I installed an air/fuel gauge to monitor the mixture and found that even with 30-weight oil in the dashpots the a/f ratio was extremely unstable when using the throttle. I figured there was probably a lot of inertial activity with the pistons jumping up and down. I put in 90-wt and the response is much more smooth. I'm using a GJ in my MKII, and that runs around 14:1 at speed. While theoretically on the money, I would be more comfortable with a little richer mixture.

Jim
J Barry

This thread was discussed between 03/10/2018 and 10/10/2018

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