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MG Midget and Sprite Technical - Why is my torque so low?

All this cam talk has got me thinking, although i confess it's idle curiosity rather than a preamble to spending money. Maybe someone might like to speculate anyway...

I had the frog RR-ed last year and while I was happy enough with the power, the torque figure seems down compared with some of the numbers bandied about on this forum.

Spec:

1293cc (not sure what the head has had done but it's P May job - I suppose I should ask him)
Piper 270 cam
Weber 45DCOE on 36mm chokes
10.2:1 CR
Maniflow zorst.

Figures from the power run after a tune up were 92bhp (calculated at flywheel) but only 71 ft/lb. How reliable these numbers are I don't know, but they're all I have.

I'm actually pretty happy with the way it drives as a fast road car, especially above 3K rpm, although the Weber is doubtless overkill for my purposes and is probably just a really efficient way of emptying my wallet whilst making a lovely noise :) Below 3K revs it's a bit gargly and doesn't really pull at all, above 3K it clears its throat and spools right round to 7K with no flat spots.

Can anyone spot an obvious problem with this spec? Is there a way of getting a bit more torque out of it without sacrificing the power I have now? If there's a little something I can do that won't break the bank I might try and budget it in for next year.

Cheers

Jordan
Jordan Gibson

Jordan - If its a PM job then it will be stamped by the thermostat - look for the number 22 or something similar (cc's)

Cam is good choice, not a lot of point in going to 1.5 rockers other than they look nice ;-) Did PM build the engine? if not then what is your cam timing set to?

Compression could come up a little bit to nearer 11:1 which would give you more bang per buck and is a cheap way of doing things.

What Dizzy do you have? that will help make more...from the sound of it you might not have the best dizzy curve - a 270 cam should pull from much lower than 3k.

Have you got the charts from the last RR session?
Toby Anscombe

Id have to agree with toby...

a ignition/vavle timing issue....curious about the intake...could be to large and/or short on the intake throat or the carb is to big

prop
Prop

In an old Kent Cams brochure their 276 cam produces 104bhp flywheel and 95lbs flywheel. That's clearly a well set up engine and did run 1.5 rockers.

So possibly a bit down and power and more down on torque. That said numbers are just numbers.

The Piper 270 is an older grind nowdays and there are better grinds out there for fast road use. As Toby says it should do more below 3K. So look at the power below 3K issue rather than the numbers.

Iv'e already said a Janspeed Controlled Vortex manifold is whats's needed for bottom end torque for another engine - same for yours. However, your's ought not to be that flat at 3K for that cam even on a standard manifold. What kind of ram pipes and filter are on the DCOE?

Daniel Thirteen-Twelve

Hi Toby

Yes it's PM built. Build sheet is at home though and I can't recall timing figure.

Was originally on 11:1 CR but was dropped back to 10.2:1 shortly before I bought the car. There are a few tuning records from the year or so before I bought it which suggest problems in getting it to run nicely, after which the CR was lowered (new Omegas). The people I took it to got it running much better than it did when I bought it.

Dizzy is an Aldon AY100. I have the RR chart but have no way of scanning it in now until Wednesday.
Jordan Gibson

Bit more info now I'm home: Regarding the head The numbers on the head are '7657 19.0 UL'. Presumably the 19 is the CCs you refer to Toby. First # the serial? UL unleaded obv. Valve sizes are stated in the paperwork - inlet 35.6mm, exhaust 31mm.

Daniel the Weber is on a Peter May manifold with a K&N oval filter 3.25" deep. Not sure on the ram pipes - will look later.
Jordan Gibson

Jordan, as you know the numbers here are simply Pub talk and should always be taken with a pinch of salt
:-))

If you believe the power is right then the torque must also be right because they are a direct relationship to each other and if one is low then so will the other by calculation! Torque multiplied by RPM equals Power.

this caculation explains that an engine at 3000 RPM is making twice the power of an engine reving at 1500RPM, a point many pub tuners are totally unaware of. So as your car accelerates from 1500 to 3000 it should become twice as powerful and would give the impression of twice the torque. Hence the reason why many amateurs suggest their engine is dead below 2 thousand. Ideally you need to compare with another car your performance.
Bob (Robert) Midget Turbo

Jordan - you could do with a longer manifold but without cutting the inner wing its a bit hard ;-)


My own choice (and that of Daniel, unless he has changed his mind) is to use an ITG filter box with full radius ram pipes:

http://tinyurl.com/4zl7g3

http://tinyurl.com/4398ev

JC20 baseplate but I cant remember the size of the filter element. If Gary pops up maybe he could pop out to the garage and measure both the filter depth and the ram pipe length.

If you can arrange transport than you can try my Maniflow which does improve the bottom end a little bit...


I would be interested in looking at the graph if you can scan it later in the week - email it me rather than posting as I dont think that the BBS can give enough resolution
Toby Anscombe

Jordan you could also come with us to the Rolling road session on Saturday and compare your engine to those of others to get a true reflection of its performance.
With all respect to Toby the tiny improvements he has refered to are not the major gains you believe you ought to have.
Bob (Robert) Midget Turbo

This thread was discussed on 13/10/2008

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