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Racing Car Setup/engine Problems - Various


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#1 Drobb1985

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Posted 06 September 2019 - 12:16 PM

Hi all,

 

I'm looking to troubleshoot a few problems with our 1380cc A-series racing car and was hopeful that some of you could give some solid advice before I go and blow a load more cash on the car...

 

Wheels/Tyres

As the bodyshell was from my first ever road car, it was paired with some 13x7" superlites that 17 year old me thought were the dog's dangly bits. As we had these wheels already, we've utilised them on the car in its current racing guise with Yoko A048R rubber. We've had a bit of a problem with the tyres rubbing on the Grp6 arch extensions (mainly on the rear) so were looking to raise the position of the arch extensions. However, I'm now wondering if it's worthwhile ditching this idea completely and switching to 10" wheels and not having arch extensions at all (similar to the App. K historics with the chrome finishing strip and nothing else). My question however is, with a Mini, is there such a thing as too much grip? I guess the general rule-of-thumb is that the more grip you have the better (up to a point), so would I be shooting myself in the foot by switching to a smaller/narrower wheel/tyre combo? I know there are benefits with regards to the "feel" of the car and the driveability, but from a sheer speed-of-cornering point-of-view, which wheel diameter/width combination would be best? Are 12" wheels even something to consider? It would also be great to have a wheel size that allows us to have a dedicated wet tyre fitted to it. The other problem we've encountered is that when we try to stiffen the Gaz dampers, the car literally becomes undriveable with the LSD dragging me all over the place and the car hopping/bouncing around corners. Possibly a symptom of having wheels that are too big?

 

Brakes

We're currently running with MG Metro Turbo 4-pots but from a previous post from Cooperman (the oracle) he reckons that the 7.5" Cooper S setup is just as good provided you have some decent pads in there. Any other opinions floating about? Obviously if I change to 10" wheels then I'll need to switch the current setup out anyway.

 

Suspension

As previously mentioned, we're running with Gaz shocks. Gaz advised that 8 clicks from the softest was a good starting point. We've tried stiffening them up but the car really didn't like it (as mentioned in the Wheels section above). We're now back at 9 all round but I was wondering if there's a train of thought regarding splitting the stiffness and perhaps having softer on the front and harder at the back or vice versa?

 

Engine

As mentioned, we're running a 1380cc with a single Weber 45, Salisbury Plate type LSD, 3.9:1 final drive, 296 scatter cam, ported/polished head with 35.7 inlet valves and 31.0 exhaust valves. It's pushing out 102bhp at the flywheel but I seem to be getting dropped quite considerably on the straights by an MG Midget which their builder tells me is pushing out 135bhp. I absolutely trust that our engine builder knows his stuff as he has about 50 years of experience but he's a specialist in twin-cams and maybe doesn't know the little tricks of the trade to get every last drop out of an A-series. I know that the Midget is using a different cam (possibly a 649) and possibly split 40s but how much of a difference could that make? I read an article by Keith Calver saying that every engine he'd driven with a 296 scatter cam was a "complete dog" so maybe that's where we've gone wrong? Anyway, the only variables where I think the problem could lie is in the cam selection and the final drive as I'm certain that our man will have nailed everything else as far as the engine build goes.

 

Tyre Pressures

We're literally putting 35psi in all 4 tyres and sending it out so any advice on general rules-of-thumb would be very well received!

 

Thanks guys!

Dave.



#2 rww

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Posted 06 September 2019 - 04:42 PM

  What form of motorsport are you competing in ? Circuit racing, Rallying, Autotest etc. 

 

 

  Are you limited in any way by the regulations you compete under ?


Edited by rww, 06 September 2019 - 04:44 PM.


#3 nicklouse

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Posted 06 September 2019 - 05:08 PM

How old are your rubbers?

Yes you can have too much grip and you roll the car.

You don’t adjust the damn pets to stiffen the suspension.

Dampers control the wheel movement.

More info needed from you.

#4 DeadSquare

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Posted 06 September 2019 - 07:20 PM

I don't know anything about Yoko rubber, but the rubber on Dunlop 10" slicks and wets is predictable, it has good feel and doesn't brake away so suddenly that you can't catch them.

 

They run at between 40 & 50 psi;  in theory, the more air, the more grip, but what you are aiming for is front to rear balance.

 

The tyre's grip is constantly being divided between cornering and traction, so that if you have understeer flat out through a bend, by lifting off a little, some of the traction grip can be released to be used for cornering.

 

It is always better, especially with rubber suspension, to have the dampers too soft than too hard, and depending on the anti roll bar, softer at the rear, and it sounds as though you may have the Salisbury set too tight.

 

100BHP per liter was the cats whisker 50 years ago, we had 83 from a plus .040" 850 Mini se7en with one 1 1/2" SU, so you are down on power somewhere.

 

We used to use a big servo from an 1800, and if I tried hard, I could lock the front wheels as "heel & toe'd" a gear change.



#5 Drobb1985

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Posted 06 September 2019 - 07:41 PM

Rww - We’re competing in circuit racing. Mainly at Knockhill but some away rounds at Croft. The basis of the regs is that the car is as per original spec with regards to chassis, block and head but carbs are free (injection is forbidden). So for example, we can have the Weber but couldn’t have an 8-port head.

Nicklouse - the rubber has only done about 30 laps. What other info do you need?

Deadsquare - Thanks for that info, especially regarding the dampers. Very helpful and something we can play around with. The bhp is a strange one. I’ve had a tuner from a hillclimb background set up the carb on his rolling road and he reckoned 102bhp was pretty good. He also said that he thought the 135bhp quoted was ******* but what I see on track doesn’t lie. They are definitely markedly quicker in a straight line.

#6 Bat

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Posted 06 September 2019 - 07:48 PM

Hi,

Discs with a larger diameter will work better than smaller if both have the same pads. As the caliper is further away from the center with the bigger discs it has more "leverage" for want of a better term.

As for the engine I've got 120bhp 100 lb/ft out of a 1380 with a 285 cam and dcoe with mappable ignition in a road going car, 40 lb/ft at 1500RPM, so there's something amiss there...

Cheers :)



#7 Drobb1985

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Posted 06 September 2019 - 08:19 PM

Bat - Well noted regarding the discs. The Miglias must use smaller discs/calipers however as they run 10x7" rims if I'm correct. And I'm sure the stopping power on those guys must be as good as you can get.

 

I'm looking at the figures from the rolling road just now and the corrected torque of our motor is 104.7lb/ft @ 5000rpm so seems to have more torque but just not the bhp. Would the cam and final drive have an effect on the bhp figures? I just assumed that power is power and variables such as those wouldn't skew the figures at all.



#8 imack

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Posted 06 September 2019 - 08:31 PM

I'm running unservo'd KAD 4 pots with standard mintex pads, 7.9" vented discs (turned down metro turbo 8.4" discs) fitted to mini drive flanges (not metro) & running 6x10 non deep dish minilites.
Work well for me.

#9 nicklouse

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Posted 06 September 2019 - 08:49 PM

Bat - Well noted regarding the discs. The Miglias must use smaller discs/calipers however as they run 10x7" rims if I'm correct. And I'm sure the stopping power on those guys must be as good as you can get.

 

I'm looking at the figures from the rolling road just now and the corrected torque of our motor is 104.7lb/ft @ 5000rpm so seems to have more torque but just not the bhp. Would the cam and final drive have an effect on the bhp figures? I just assumed that power is power and variables such as those wouldn't skew the figures at all.

why? they rarely use the brakes.

 

by the way when i said Rubber i was on about the cones not the tyres if that is what you answered to.

 

back to your comment about the tyres rubbing on the arches do you mean the add on arches or the body shell?



#10 rww

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Posted 06 September 2019 - 10:36 PM

  The best advice to you can only be based on current personal experience. Often that experience is built up over many years and the associated budget is spread over that period. You need very deep pockets indeed to build a competitive and reliable Mini in a short timescale.  The following is pretty generalised because over the years the Mini has been developed by some very clever people. I wish I was one of them.

 

Suspension. Minispares yellow spot cones all round. Rear arches 'tubbed' ie flat, no outer edge. Subframes solid mounted in all respects.Size of rear anti-roll bar to suit grip of tyres. Rose jointed front suspension. Approx ride heights 7.25"front, 8.25" rear , rear toe parallel/slightly toe out with 1 degree neg camber, front geo. parallel track, approx 2 degrees neg, approx 6 degrees castor. Standard rack will suffice with rose joint ends and bump steer mod to lower steering rack end in relation to the hub steering arm. Front hub lower ball joint extension piece. Dampers are probably the key (and very expensive) item that will improve cornering speed in keeping the car flat. When I spoke to Quantums to get our fronts revalved to latest Miglia specs I said to the technician that they were already so stiff they were acting like another spring. He did not disagree. Yes, of course they absorb bump and rebound movement but they must surely slow it down significantly. Ours are set almost max hard front and rear, the rears a bit softer than the front. If you have rebound adj on the front then this can be set mid-range.

 

Tyres. The Miglia Dunlop slicks are the most developed race tyre for the Mini. We have used them in the Mig Invitation races. Pressures are around 30psi. The race series we do now only allows Yokohama tyres. The 12" AO48R to my mind is a fantastic tyre. About 2 secs a lap slower than a mig it will last almost a season of races at around half the cost of a Dunlop slick. Yoko recommend an operating range of hot pressures between 28 - 32psi. We try to operate at the lower end of that window. The suspension set up for 10" and 12" is pretty much the same as the tyres are a similar rolling circumference.

 

Brakes. Simple. KAD 4 pots, 7.9 " vented discs and Minispares carbon metallic pads. Ultra reliable, fantastic stopping power, no fade with a high temp fluid. Fit and (almost) forget. Standard drums and linings at the back with a balancing valve at the rear to reduce rear pressures to prevent wheel locking. With a car capable of 110 -115mph you really do need strong brakes at the end of any straight.

 

I suspect that your 13" wheels/tyres are giving you a suspension ride height that is too high, despite the fact that in theory you will have more grip with the wider tyre than a 12" Yoko. Our gearbox is damn close to the ground, but doesn't hit the kerbs. I would, for the moment, set aside development of the engine as I suspect that the car is just not able to go around the corners quick enough or be driven with great confidence and commitment. If budget constraints apply then set about getting the car as low as you can, you may have to move the front damper mounts and need shorter dampers to do this. The tubbed rear bodywork probably allows a further inch of lowering. Unfortunately, where you are in Scotland, there are probably not many places to offer suspension set up but I suspect that this might rid you of the self steering and unpredictable handling you appear to have at present. Best of luck.



#11 rww

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Posted 06 September 2019 - 10:38 PM

Bat - Well noted regarding the discs. The Miglias must use smaller discs/calipers however as they run 10x7" rims if I'm correct. And I'm sure the stopping power on those guys must be as good as you can get.

 

I'm looking at the figures from the rolling road just now and the corrected torque of our motor is 104.7lb/ft @ 5000rpm so seems to have more torque but just not the bhp. Would the cam and final drive have an effect on the bhp figures? I just assumed that power is power and variables such as those wouldn't skew the figures at all.

  

 The cam will certainly effect your power output. The final drive ratio will not.


Edited by rww, 06 September 2019 - 10:51 PM.


#12 nicklouse

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Posted 06 September 2019 - 11:31 PM

just noticed you have added a profile picture.

photo-122592.jpg

looks way high. looks like there is a fair about of bump steer looking at the angle diff between the inner and outer wheels in that pic.

rear does not look like it has been tubbed so you will have body tyre issues.

as mentioned above is single adjust shocks you can over damp the suspension and the shock will pack down. pulling the wheel up into the body during repeated bumps.

 

but what you can do depends on what the regs actually say.

 

re the engine i would say you are down 20+bhp with that spec. and i would be interested what Keith meant by "dog"



#13 Drobb1985

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Posted 07 September 2019 - 10:19 AM

imack - thanks for the tip. KAD 4-pots certainly seem to have a lot of fans.

 

nicklouse - they rarely use the brakes? I'd have thought that a Miglia is the most developed racing Mini so surely their braking system is similarly well-developed, albeit limited by regs. The rubber cones were brand new at the start of the year but as far as I can recall are just the standard ones. And it's Grp6 arch extensions that the tyres are rubbing on, not the bodyshell. The regs for our series are pretty loose to be honest - we can't have a beam axle or coilovers but other than that it's free. In your opinion, do you think having the wrong cam in could result in a loss of 20+bhp or is it likely that it's a few things in addition to that?

 

rww - thanks very much, that's a really helpful reply and a lot to give us discussion points about. I did have the geometry set up by a professional and pretty much exactly as you've noted with regards to camber/caster etc which made a big difference. It's the ride height that we've not been able to do anything with and as you say, will be due to the original arches not being cut away at all so that's something I'm going to have to do. 



#14 nicklouse

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Posted 07 September 2019 - 10:28 AM

It ain’t the cam. I have the same and speced a similar one in a 1380 that did a good 140+

If you are rubbing on the extensions reposition them. Or fit some means of stopping the travel going that far.

Nowt wrong with new original rubbers.(there are some ******* ones though) it was all we had in the 90s and they worked.

Brakes are less important in the circuits than in something like hill climbing but we can go bigger and that helps and we need them to work from cold. If you are getting brake fade then yes you need to look at changes. Most 13s will take a 10.5” disc think on.

Never been a fan of the Salisbury diff.

What inlet and exhaust manifolds are you using? And the head who did it?

EDIT: just to add to the brakes comment. You should be looking to make the car corner as fast as you can before looking at brakes. If you are having to brake to get around a corner then your set up needs looking at. Long straights into corners excepted. Good brakes do not make you fast. Good suspension set up does.

Edited by nicklouse, 07 September 2019 - 10:48 AM.


#15 imack

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Posted 07 September 2019 - 10:47 AM

Your car looks way too high in my opinion in that photo. You can run them pretty low on 10" wheels without tubbing the rear arches and without rubbing issues if it's not used for carrying passengers. I'm not sure the 7x13's will be doing you any favours as I'm certain they will be messing up scrub radius along withe the metro turbo drive flanges if you're using them.
Are you using mini front hub carriers or metro ones with sealed ball joints? I think the metro ones mess up kpi and bump steer.
I got rid of the turbo drive flanges and 1/2" of wheel spacers from the front of my 1380 649 cammed quaife diffed road car and it transformed the car and almost eliminated the weaving and dragging from one side of the road to the other it had under acceleration over cambered or uneven surfaces.
Nothing wrong with a 296 cam, is it timed correctly? What rockers? Think it's designed for 1.5's.
Inlet valve possibly a little on the small side although I thing miglias and historic are limited to these sizes and they supposedly make 130 -140 bhp.




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