Race vs street tuning, and drivability?

[Lyngeled]

Hi
I have tried to find out what is meant by some saying that a race tuned engine is less "drivable". I think that I have read that such an engine is not good i normal traffic with lots of stop/starts and queing. But how? Or is it as some says that the engine will have to be adjusted or rebuild more often?

Regards
Lars

[Serge]

Out and out race engines, will have very little torque down low. Power is also very high up in the power band, so power would maybe start at 4K or 5K RPM, under that it would be very slow to pick up. Therefor this engine would be difficult to use in traffic.

With a real hardcore racing engine, clearances will be set looser, because everything will expand more, because of more heat (harder use), this will require more frequent rebuilds.

Serge

[BDA]

The difference in what is desired in race and a street engine is not only the amount off power and torque but the range where there that power and torque is available. Most race engines produce the majority of their power at elevated rpms since that's where it's needed.

A lot of this is because of the cam - racing cams have higher lift and longer overlap. This means that the exhaust and inlet valves are opened wider and are open at the same time for a longer period of time. This is necessary because of the time it takes for the inlet charge to completely enter the combustion chamber and the time it takes to expel the exhaust gases. Another change is the size of the valves, inlet and exhaust manifolds and the carburetor or fuel injection flow rate. The fuel air mixture requires enough velocity in order to effectively mix properly. Race engines are setup to move much more air and fuel and can mean that the inlet and carbs or injection are too big for sufficient velocity at the lower flow rates of a street engine. Of course the exhaust manifold of a race car is sized for extracting the exhaust taking into consideration the rpm where the power is wanted and the amount of exhaust. A racing exhaust would not cause a problem on a street engine (other than the noise) but it would not be as efficient as it would be on a race engine. The compression ratios used on racing engines generally require fuel with higher octane numbers.

In some cases, doing all the tuning and modifications to make a race engine will make it hard to start and very temperamental in a street driving situation. 

On the other hand, there are some things that are done on a race engine that are useful on a street engine. The machining tolerances help reduce wear and friction compared to most street engines - though I wouldn't be surprised that the gap between the accuracy of the machining between racing and street engines has decreased substantially in recent years. 

You didn't ask about the rest of the car, but there are other reasons why racing systems are inappropriate for street use. For example, most racing transmissions use straight cut gears which are very noisy and they do not use synchronizers complicating stop and go driving.

[JR73]

It can also be down to personal preference, depends on what you are expecting from the engine along with how you intend to use the car?

If you are after refinement and ease of use etc then you probably won't enjoy trying to use a highly tuned 'race spec' engine - wild cams for example don't generally allow for a smooth tick over whilst left to idle, likewise lightweight flywheels along with uprated 'grabby' clutches require a little more concentration when filtering in stop start traffic in comparison to those fitted as standard to the majority of road cars...

A well built and set up race engine can be quite useable on the road - even more so if you have decided that you want such an engine! - the question is WHY you need such an engine in a road car? Race engines are refreshed/rebuilt quite often not only due to the hard life they experience on track but also to keep them delivering the power they where built to produce. - if you can't use all of the performance it can deliver where you intend to use the car then do you need to spend the money on having the 'ultimate' spec for that engine?!

Personally speaking I have a full race spec engine in one of my cars and I love it! - it's quite ridiculous in so many ways but that is also why I like it so much! Likewise, I don't do 20k miles in it a year or intend to use it for that many miles before stripping it and refreshing it. I can however use it (and more importantly to me enjoy it) quite easily on the road and find the driveability of it quite acceptable.

[4129R]

4 valve per cylinder heads make highly tuned engines much more tractable at low revs.

[jbcollier]

I guess it all depends on what you mean by race or full-race tunes.  A K&N air filter and a noisy exhaust isn’t going to make much difference in driveability.  If your engine won’t idle at less than 3K rpm and outright stalls unless you rev it to 5K before you dump the clutch, it may not be the best choice for stop and go traffic.

[Lyngeled]

Thanks for your replies. I now understand the meaning of less drivability. My interest is because I have been told that my engine is tuned and done a lot of things, but I am not sure how it “should” be driven. It has not those problem you describe with idling, it’s idling very fine. It does not feel that unusual compared to what you discribed.

Regards

[BDA]

Without knowing what was done to the motor, it would be difficult to say how it should drive but the fact that it idles smoothly is a good sign. If you could describe some of what was done or tell us what you have - what size carbs, for example, would be very helpful in predicting how driveable it might be.

I had an MG Midget race car that had a motor that would probably have been reasonably driveable. It had a pretty flat torque curve so there was reasonable torque throughout the rev range. I suspect that was because I was limited in the size (and number) of carbs.

[Lyngeled]

It has 2xDellorto 45 and Extractor Exhaust. Could be some more things done too, I am not sure.

Regards

[BDA]

I guess I should have also asked what engine you have! We also don't know if your car was meant for racing or the road when you got it (does it have or have provision for a muffler?), if you got the engine separately, had it ever been used and how...

If you have a Renault motor, that sounds like a lot and is probably a lot for a TC. I was discussing my carbs (45 DCOE) on my BDA motor on the yahoo group, sidedraftcentral and the moderator was surprised my carbs were not 40s which was the size Ford used on their BDAs in their Escort RS1600 street cars. They work fine in my engine. I would expect the 4 valve head that I have flows a lot more than the TC or any of the "standard" Renault motors generally found in a Europa and that would be why they work.

I'm couching my language here some because I am by no means an expert so as far as I KNOW, it could be that your motor would be fine on the street. I'm guessing that you haven't been able to drive it yet and that you're somewhere between receiving your car and getting it ready for the road. I would probably put the car together and drive it and see what it's like. If it doesn't workout then you can make some decisions.

All that said, I know we'd all like to hear more about your car and motor. (We'd like to know that regardless!) Maybe someone here who has more knowledge can help you more than I can.

[Nero]

45 DCOE are not uncommon on Alpine A110. They fitted them on 1600 engines but they reved higher so they make kind of sense. You can argue about that all day long.
For example, my fathers S2 runs with a modified Renault engine. It's standard crank but with bigger bore, different pistons and conrods to give longer stroke that brings it to 1760cc, bigger valves, ported, also a different exhaust, but still only running on 40 carbs. Most people got the 45s because the A110 got them and the engines are mostly overcarburated.
You need to know a lot more about your engine to judge the size of the carbs.

[Lyngeled]

It is a Renault 807,  I have asked earlier here, I think, about it using so much fuel. I have been told it was tuned in Sweden by Arne Berg, Bo Hellberg listed up for me, things that may have been done.

I have been drivning it, and does still (not now with Winter weather and salt), and I have found out that it is ok good shape, but still something need to be done to the engine. Using too much fuel and then I think it could produce more power. It will be when I do something to get first and second gear when I want to. I bought it in 17, and I am getting to learn more and more about it.

[BDA]

This might contain some interesting information:

http://www.lotuseuropa.org/LotusForum/index.php?topic=1748.0

[jbcollier]

A pair of sidedraft 45s were standard on the 807 engined R8, R12 and R17 Gordinis, as well as the Alpine A110 1565, 1596, 1605 and 1647 engines.  Fitting 40s (as I did to mine) fattens up the lower end a bit, improves economy and doesn’t take too much off the top end for street use.  If I was racing, I would fit 45s — and still lose.

The best thing I can recomend is to fit a wide-band O2 sensor and an A/F gauge.  No more guess work and you’ll be able to dial in the jetting perfectly.