Driving to the circuit in a comp car: yes or no?

[miro-1980]

Hi guys ,

I just had a visit from a friend and direct competitor , who drives a Ritmo 130 TC.

We talked about plans for new season and this friend (call him Jerry) suggested that if I put in my 131 abarth (replica) a 180bhp engine, on forged rods and pistons, abarth diff with 6.14 LSD ( 8/43) , 40 % uprated pressure plate and metallic clutch with springs I will hardly be able to drive the car 200 miles to get to the track day or rally event, could destroy my LSD in the process, will travel at low speed and high RPM for hours and the only thing for me to do is to put he car on trailer (carrier towed behind my car).

Is he scared I will beat him this season or is he has a real point ?

In other words: what will these modifications mean to normal driving . ( I do not intend to drive the car every day , but will several times a year have to travel to the racing site ( several hundred km each time) =go to my mechanic in the city, etc. How will these modifications effect my ability to do so, etc

What about LSD? Is a car with LSD (adjustable) drivable in normal trffic?


Any thoughts , experiences ?

PS : GC suggests that what I should look for is a higher ratio diff ( i.e 10/3) and a close ratio gearbox to get to ca. 100 kmh in 2-nd gear.

[mtbr]

Miro,
I haven't looked at your specific gear ratios, however "lowering" the final drive will result in a lower maximum speed (limited by the engine rpm rather than drag vs available power), higher fuel consumption and probably driving more slowly on the road sections. It's normal for the practical considerations of reduced range per tank of fuel and noise in the cabin, rather than potential mechanical wear and tear, to slow you down. You can easily look up what engine speed will be required for a given cruising speed and final drive ratio, using the spreadsheet Guy provided.

A couple of fuel cans in the boot and a set of noise canceling headphones, go a long way to mitigating the above practical disadvantages. Once "on event" you will be glad of the extra acceleration!

There is no reason why your limited slip differential should be damaged by road miles. Provided you drive without provoking wheel spin, on the road sections, the differential will behave more or less the same as an "open" one. There should be almost no additional wear.

By way of illustration, I have a Salisbury type LSD in a 300 bhp Porsche 993RS that has spent almost all it's life on "trackday" tires, (the rears are 10" wide). This car has done over 100,000 km and the diff is on it's 2nd set of plates!

[miro-1980]

MTBR ,

Thanks a lot , this means the competition is fearful (LOL) ..

but seriously speaking: how much it too much and how little is too little.

In other words, could you recommend which diff ratio would - on one hand give me very good acceleration , but at the same time give me some speed. I typically expect the top speed on our racing events not to exceed 100 kmh (not very high as you see).

Also on the track - the way we do it - there are a lot of tight shikanes - which are to slow us down (for safety reasons).

It appears to me that acceleration is the key wining factor in these events. The straights are not long enough for the top speed to really matter. For instance in most events I rarely go into 4th gear ( and when I shift into 4th I typically regret it when I see the stage results. Practically all of the events are driven on 1st, 2nd and 3rd gears.

(see viewtopic.php?f=6&t=1787 for details of the couses and our runs)

PS: Clsose ratio gearbox – an issue to which GC alerted me already - another matter

Any ides ?

I am attaching a full set of tables and graph I created showing engine speed at different diff ratios.

[mtbr]

Miro,
I will try to post another spreadsheet that you can use to generate cascade curves of drive force at the tire contact patch vs road speed, this evening. (I am busy putting my Lotus race car back together just now) Using a combination of cascade curves and the speed vs rpm charts you already have, will allow you to better visualize how gearing works.

Mark

[Guy Croft]

Hullo Mark!

Long time no speak. They let you off the boat now and again, yes?

My advice, Miro, is definitely trailer the car to events. No reason with your spec (clutch, engine) why you couldn't drive the car to events of course, none whatever. Might be a bit tiresome that's all, wouldn't care to say, 180bhp would not be unduly 'peaky' to drive with a 2 liter. Not one of mine anyhow and I've driven enough to know. 200bhp, well maybe, depends on the powerband. The LSD will make it a safer car not the reverse. It's just that it's not much fun being stranded 200miles from home at a windy circuit with a broken race car.

I'm no fan of road-race because a well-prepped race car is no fun on the road (changing gear every two minutes) and a road car is no fun on the track.

GC

[miro-1980]

Dear GC ,

Your phrase : "well-prepped race car is no fun on the road and a road car is no fun on the track" says it all and appears to be the name of the game.

Thanks a lot, again.

Miro