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MG Midget and Sprite Technical - 1293 Fast Road Output

I requested info on an Oselli A600 cam.
Richard Wale, kindly sent me a spec sheet for Oselli fast road engine (which is what my unit is) - it shows a dyno for 95hp !

Well at Aldon last weekend (MGCC event) mine knocked ou 76hp - did note a problem with the dizzy advance and was at lower revs + only covered 1500 miles.

The spec sheets recommends 1.75 or DCOE45 - I am currently using 2x1.25 with K&N's.

Is a change to a HIF6 and titan+K&N (which I have) going to add significant more power ?- seems too good to be true !

If I change it and r/r it would certainly be good back to back testing.

R.

richard boobier

I wouldn't expect it to make that much difference but it would certainly make a good back to back test.
I love to hear about exact back to back testing of any change.
Robert (Bob) Midget Turbo

May be the difference between flywheel hp and power at the wheels - generally it is thought that the transmission will absorb about 1/3 of the flywheel power...?

I wouldn't have thought a carb change would make a massive difference in output although it may be advantageous... You will need the correct needle/spring in the HIF6 to get maximum benefit so a RR would be a good plan.

Cheers

James
J A Bilsland

I thought that was a possibility James but I have seen the info from Aldon RR and Richards BHP was flywheel power.
Robert (Bob) Midget Turbo

If you were running a lower rpm than the one in the test, you WILL have a lower HP number. Yes, you can guarantee that the engine tested was on an engine dyno rather than a chassis dyno, and that the builder was more concerned with peak HP than with drivability or longevity. Yes, modern chassis dynos can do a fair job of estimating flywheel hp, but it is still an estimate.

OTOH, if the advance was off at the rpm involved, you did not see peak hp. Might be interesting to compare the torque curves...

The 1.75" SU can enhance your peak hp as well, since it's peak flow is better than that of a pair of 1.25" SUs.
David "HP is just a number"
David Lieb

The class C midget challenge cars run on flowed 1.25" carbs and put out about 100bhp. Won't take you too long when you follow Vizard.
John Collinson

Yes but what were the torque figures? yours vs spec.
Tarquin

Torque was fairly consistant from abot 3k to 5k revs @ about 80 lbft.
Don't have a curve in the brochure.

R.
richard boobier

Probably some of the difference will be in how good the cylinder head is on your engine. I'd expect they ran a higher CR than your engine runs. They may have spent a lot of time with lots of small mods to get optimum power for that cam. It's also possible they didn't run a dynamo or generator etc, etc.
Daniel Thirteen-Twelve

76 bhp seems rather low - -IIRC the original BL spec was 72 bhp for a standard 1275 in the Mk3 Midget.
David (davidDOTsmithAT stonesDOTcom)

My brochures note 64/65 for 1275 in the 70-73 ranges.

R.
richard boobier

Hi David

72 bhp standard from 1275? I think MG/BL quoted 65. Or do you mean 72 lb-ft?

Reason for low power? Well the torque drops away too quickly from 5K onwards:

- your engine may still be a little tight; additional friction = power loss

- it's running weak above 4.5K (should have been found on RR, but of course twin carbs make this process harder)

- ignition timing optimised for mid-range and not for 5K+ (again, 'swinging' the dissy a 3, 4, 5, and 6K would find how far out is the mech advance curve, and the best-fit timing for your engine and dissy; do you know the dissy spec?)

- breathing cylinder head/inlet/exhaust (as pointed out)

- cam timing not optimised (might be worth measuring the open-close of inlet valve and compare with spec (I'm not concerned so much with the duration but whether the cam is too advanced or retarded; this is cheap to do yourself)

I'm always amazed to hear 100 bhp from twin 1 1/4; amazed since the standard manifold pattern does not allow sharing between carbs, so this is 100 bhp in effect from single 1 1/4. Vizard points out that the std manifold is exceptionally poor. (But I'm not disputing 100 is possible)

I'm a big fan of the single 1 3/4; as was MG in later engines. Like others, would like to see back-back comparison with no other changes.

A
Anthony Cutler

Anthony, there are some additional mods not in Vizard including reaming out the balance bar to help with some extra "pull" from the other carb.
John Collinson

good job I said 'IIRC' as I didn't ! Yes 72 is the torque.
David (davidDOTsmithAT stonesDOTcom)

John,
Those mods are interesting, but not probable for anyone who has the option of using the 1.75" carb. If one must have dual carbs to satisfy the requirements of a racing class or simply because one likes having the sexy look of dual carbs, those can make it better. If, however, I wanted to get more hp out of my engine, the stereo effect simply does not cut it.

If you look at the pulses in the intake manifold, you can see that you will see that it pulls twice through the front carb, then twice through the rear carb. Effectively, the airflow through a given carb is stopping and starting much more than the single carb application. This is significant.

Also if you run the numbers, the total throat area of two 1.25" carbs is 2 times pi times .625 squared (approximately 2.45 square inches) vs pi times .875 squared (approx 2.40 square inches). Minimal difference, and as Anthony points out, no one cylinder will see the full effect of both carbs, no matter how big the balance tube.

For street use, there isn't a huge difference, but when you are on a dyno, revving to rpm that you are not likely to actually use on the street, this will certainly affect peak HP. Whatever engineer it was who decided that siamesed intakes were a good idea is not appreciated much these days...
David "still running HS2s" Lieb
David Lieb

I've attached a pic of the r/r sheet.


The check was obviously not a full r/r session as time was limited by needing to get through all the other guys at the session.
My dizzy was found to be faulty (over advancing) and was not able to be sorted in the time.

Ant,
I think you may well be correct that I am running lean at higher revs - will try AF (currently AH2) needles which are noted in vizard for similar build.
The cam hopefully is set correctly as Oseli built the engine and included a vernier set up. The head is an Oselli stage 2.
The r/r went to 5200 so if lean and incorrect timing + I think the operator was a bit kind as the engine was fairly new.

So the plan is take it back to Aldon (Peter Burgess is a bit to far)recurved / new dizzy, AF needles and have a full tune.
If that does not sort it I'll try another day with the HIF6 - want to do it slowly and find out what is best.

Does that sound a good plan or am I wasting time not just going for the HIF now ?

R.


richard boobier

Richard
Time spent on a rolling road comparing tuning parts is never wasted. Knowledge is priceless and when comparing items on a rolling road then you are adding to your knowledge.

If you can afford it then do it please for me at least. It is a test I have never done.
Robert (Bob) Midget Turbo

The dip in torque at 3,500 is a concern... due to weak mixture, ignition curve being non-optimal or cam timing...

A
Anthony Cutler

to my eyes the torque does seem on the low side for a 'fast road' engine.
Tarquin

David,
I agree. The advantage of the twin carbs is that they came with the car (i.e free) and can be modified at very little cost if there is a tight budget or as you say you want the original look.

Richard - I have never come away from a rolling road session thinking it a waste of time/money. Whether squeezing a few more hp (e.g milling the top of the piston so it completely rises rather than chamfering the lower edge) or just seeing if urban myths are true - like sock filters sap power (on both S.U's and Weber found there to be no difference with or without sock filters).

John "I now run on split webers" Collinson
John Collinson

I am certainly a massive fan of rolling roads. When we first put my Hif44 on my Frogeye. It was running so lean that it wouldn't go any faster than 70mph. Something was so obviously wrong.
My engine is 1330 with very boring AE standard pistons, the only bit of machining has been getting the main bearing strapped. It has a very good Peter May head, a 123 distibutor, a nice exhaust system and an ok air filter.
My first run on the rolling road gave a meere 77 at the flywheel and about 55bhp which showed that something was clearly wrong.
Two hours, multiple runs and only £100 later I left with the following printout.
A £100 well spent I'd say.
As I'm rubbish at reading graphs, I'd be interested to hear peoples comments. I think that the little judders at the end of the graph might be me losing my bottle on a relatively (less than 1000 miles at the time) new engine.


Gary Lazarus

that's it

I'm not putting my baby on the same road as your big bad bully of a car


or:

nice!

(were you driving the throttle yourself? PB never let me do that!)
bill sdgpm

Yes I had about 15 runs with me in the car at all times.
Gary Lazarus

Gary,
Looks as if you have a rev-limiter on there? Yes? No?
If so, looks as if it is pretty much sorted from 3000 up. As a street driver, I am a bit concerned with the torque curve at 1700 and 2200 or so. Looks as if you are losing a lot of driveability there. Too bad the RR operator did not see fit to throw an O2 sensor on and graph it as well. Can be very helpful at pointing the bone in terms of mixture vs ignition timing.
David "nice curves!" Lieb
David Lieb

I thought that was simply Gary changing gear and getting the rollers spinning in top gear isn't it?
Robert (Bob) Midget Turbo

No rev limiter and I was flat out with my foot to floor.
Bob's correct, I was changing up through the gears (not using fifth)
I have a kent 276 cam and a 3.9 dif.

In terms of drivability, the pick-up from 60-90mph (on track) for overtaking is so very responsive.
Do you think that it should be revving higher than that?
Assuming that I wasn't lifting off, why the flutter between 6000-6400?
Gary Lazarus

Hmm, here they usually use third gear and the curves don't start until in that gear, so no gear changes to be seen.
David "not saying that it is better that way..." Lieb
David Lieb

20HP for 100 squids is real value. If you can find that as a bolt-on I'll take two please. Gary your curve suggests nothing to be gained revving beyond 5500rpm (until you get into top gear of course). The technician might have a clue re the flutter from 5800 onwards but I dont. For road use I'd be more concerned with chasing that dip from 2000-2500rpm.

With Richard's engine the dip from 3000-3500rpm might disappear with tweaking ignition advance curve and/or mixture. Also the graph suggests the power isn't finished at 5000. I like to see it run until it's definitely over the hill. That flat torque line looks good.
Mike Allen

The 5800rpm dip on Gary's engine could be "points bounce"? Or perhaps it is using the fuel faster than it can get to the carbs? No no no, it must be the condensor ;-)
David "built-in rev-limiter?" Lieb
David Lieb

Hi Gary

Were you driving the car on the rollers?

Peter
peter burgess

Do 123 dizzy's have points?

Does look like a high speed misfire of some type? Or your right foot was lifting when your brain was telling it to stay down (take it from a racer it happens!)

Gary are you running a standard cam? If so you won't see much benefit in chasing higher revs - you might pick up some torque lower down with a different advance curve?

James
J A Bilsland

Peter,

Yes I was driving the car on the rollers.

James,

Yes it's a 123 dizzy and no it doesn't have points.
The cam is a Kent 276

I really tried to keep my foot down so I'm 50/50 on whether I subliminally lifted off.

Thanks for the feedback and sorry for hijacking Richards thread.
Gary Lazarus

Gary,
Since it isn't points bounce and there is no ignition condensor in the equation, is it possible that your engine is sucking fuel in faster than your fuel pump can get it into the HIF44 (see, I DID read some of your posts)? What are you running for a fuel supply? SU pump? Regulator? Standard inlet valve (not grose-jet)?

If it is an electric fuel delivery, have you measured the gpm?

I would be tempted to try it again with a higher pressure pump and a good regulator near the carb, pushing 3psi or so at the carb.
David "out of gas" Lieb
David Lieb

Standard pump (click click),standard valve and to be honest I'm only pushing the speed off the clock a couple of times a year on trackdays and perhaps the occasional French motorway. As mentioned earlier, the car's pick up from 60-90mph is as responsive as I need it. So all in all I'm very happy with the way that the engine feels.
Mr Burgess may well be getting a call from me next spring to see if a roll on his road might benefit the car.

Though I think that more benefit is to be gained by tweaking my brakes, ARB and suspension before I go for more power from the engine.
Gary Lazarus

Hi Gary

I think the rollers are just giving you spikes and maybe nothing to do with your driving, this is why I asked if you were driving, experience would have ruled out driver error. I am a little wary the operator was interfaced ( as they say in IT) to car throttle, brakes, gears and engine switch off via first time rolling road driver. With the best will in the world I don't see how it works. I know my rollers are water brake and therefore load governed, not speed governed as in eddy brakes but I would have thought experience was needed, then you wouldn't be asking what the spikes are. Didn't the rolling road operator tell you what was happening? It may be a fast speed run up you were doing which with the hysteresis of thge rolling road and being at the end of the run would probably give spurious readings. remember you are not reading bhp but an interpretation thereof based on torque and work done in time taken.

Local place had just installed a second mobile rolling road to take to shows, one shows 25 bhp more than the other how can that be when the bhp is the same?

Peter
peter burgess

What a great read.

Following on peter burguss comments.

What should the Avg. persoon look for in a rolling road Shop/business, and what should be avoided? Does it matter if they have never seen a midget, let alone Su carbs?

Im also wondering what prep work should be done to a car before going to a rolling road? aka...tire condition/pressure, Age of fuel, season of the year winter vs summer, new spark plugs vs. old, percentage of anti frezze to water ratio, exhaust leaks, fuel filter condition, bonnent up or down, ect. ect.

The reason i ask, is there is a new Rolling Road shop that just opened about a year ago just down the road...Im sure they have never seen a midget and SU carbs. they primarliy work on Race cars..AKA dirt track sub-nascar racers and the occasional hot rods of american muscel and alot of the popular hot street rice burners. So The idea of sticking the midget on there rolling road at some point is an idea Im thinking...but not vary well sold on it at this point as Id perfer a place that has alot of experiance with brit engines, but I have no clue to where there maybe one in the midwest of the USA

Prop
Prop

Gary

As you point out you're very happy with the improvement in power and tractability you saw from your RR session so I wouldn't worry about what the graph shows - what the engine does on the road and the track is far more important than spurious power figures (As Peter points out who would want their car run on the 25bhp less rolling road? - but the fuelling and ignition set up would be the same and the car would in reality feel the same on the tarmac road...)

My race car has never seen a rolling road - the engine/carb/ignition was set up on Swiftune's dyno 10 years ago and every time I rebuild it I set it back up on the same timing settings with a Snap-On timing light - it may be that I could improve on my power by a few bhp with a decent RR set up, but it has never seemed to be a priority - I'm running close to the front of my class of the Midget challenge and beating cars with (apparently) over 130bhp at the wheels... it may be that next year I succumb to the temptation of more power in an effort to run at the front with Mark Turner and Dom Mooney but we shall see...

You're right by the way in suggesting that you will get much more improvement in the way the car drives on the track with suspension and braking mods, than you will ever see by way of power hikes - (given you have already spent the best £100 and got your engine close to where it should be on set-up)

Cheers

James


J A Bilsland

Hi Prop

As you said do all your list, try to get some 'right ball park' needles and get some figures from the rollers, with emissions and timings then others on the threads may be able to help you if the rolling road cannot.

Hi James

The only thing I would say is fuels have changed quite a lot over the past 10 years so you may well get, if not more bhp then peace of mind reliability. Maybe the ones winning have been on the rollers more recently?

Peter

peter burgess

Peter

Absolutely - likely there is more power to be found and I suspect I will be running it on the rollers once the winter rebuild is complete - so far as reliability is concerned it has done pretty well - the same engine (with rebuilds in between!) won the FISC series in 1999, Class B of the Midget Challenge in 2002 and came 3rd in class B again this year - it had a rest between 2003 and 2008 after my old car was totalled at Dijon... :)
J A Bilsland

Gary
Those blips at the top end of your dyno sheet are caused by loss of traction on the rollers. Most likely a wheel balance issue, perhaps a flat spot on the tyre. Got the same result with my new one this morning. Picked up 5hp just by changing the air jets. And yesterday I discovered it can lose 6.4kg by tossing out the side mounts on the seats and bolting the seats through the floor.
Let the games begin.
Taking it to Lakeside on Wednesday for a shakedown run, and to get a bit of seat time. Ran it up the road yesterday and it feels much different from the yellow car, more like a fast road car than a race car.
Lakeside: http://en.wikipedia.org/wiki/Lakeside_International_Raceway
Mike Allen

Hi Mike

Interesting observation, when the tyres lose grip on my rollers I get ridiculous readings, same if the car rides up on front roller, on my Clayton the front roller reads torque and the rear roller reads speed, torque times speed equals bhp . If one roller doesn't run at true speed then readings are wrong. This is the local knowledge I was trying to explain to Gary when he was allowed to drive the car on the rollers. I get a feel for how the car is running (23 years rolling roading!). I can feel the rear tyres when they patter, they must have to be very bad to give spurious readings.

Peter
peter burgess

Peter, this was a Dyno Dynamics unit with a single roller for the drive wheels.
Mike Allen

Hi Mike

It is good the operator could tell you the problem, we sometimes have buckled wheels or out of shape tyres and even though the customer cannot feel the problem on the road they can see for themselves on the rollers.

Peter
peter burgess

This thread was discussed between 27/11/2009 and 04/12/2009

MG Midget and Sprite Technical index

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