MG-Cars.info

Welcome to our Site for MG, Triumph and Austin-Healey Car Information.

Parts

MG parts spares and accessories are available for MG T Series (TA, MG TB, MG TC, MG TD, MG TF), Magnette, MGA, Twin cam, MGB, MGBGT, MGC, MGC GT, MG Midget, Sprite and other MG models from British car spares company LBCarCo.

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

MG TD TF 1500 index

This thread is from the archives. Join the live MG TD TF 1500 BBS now