Tweaks to low power engines

[Ntrprise]

I've spent the last 18 months designing a 750 Formula car. The league is intended for people who want to design / build and race their own cars.

One of the few regulations is the engine. There are only 2 choices. I am going with the 1108 Fiat Fire engine. Although this meant to have more torque then the other choice, it is still low power. I know that on a track, it will lap quicker than a BMW M3 if running in good order. Top end is probably 115-120 MPH but agile as a cat.

Most my experience is with suspension and chassis set up as well as air flow management..... Engines are not my strongpoint.

My question is this - What is the best way to squeeze an extra few hamsters out of a low horsepower engine. Turbo’s are not allowed. Ideally, not many specialist or expensive tools required.... Any advice?

[kickstart]

If you are permitted a very good idea would be to blueprint the engine and balance the crankshaft. A huge amount depends on what the regulations allow. If the engine cannot be properly modified eg camshafts etc then you need to make sure that the engine is running at its optimum.
Think about carbs are these free ? If so webers are often a good move. What about airfilters, spark plugs, ignition leads, removing the cat convertor, special exhaust etc.
Whatever you do I would really recommend speaking to someone at the 750MC who could point you in the right direction.
Lastly when you have done up the engine get it properly set up on a rolling road - which will give you an honest power output/torque figure.
I suspect that you may find it worthwhile to entrust the engine to a decent engine builder to get it properly prepared as it is such an intergral part of the car.
Have fun

[KC]

The easiest ways to get more power from any engine is to increase its ability to intake and exhaust. Larger mass air valves (fuel injection) or carburettor intakes coupled with larger intake and exhaust valves flowing through a larger exhaust system will all increase power. However, there is no such thing as free power. To get more horsepower from a given engine it will probably require a reduction in available torque ar at least a redistibution of torque to another area of the rpm band.

Camshafts can also be used to increase the duration (time the cam holds the valves open) and lift (distance the valve is opened). However, there are tradeoffs here as well. The wilder the cam is the less rpm the engine will be able to make without adverse valve float (a condition where the valve springs cannot keep the tappet or roller in contact with the cam lobe). The more lift and duration an engine has the more air that can be added to the mixture. However, it also takes more valve spring pressure to compensate and this increases valve train friction. Always a trade off.

Depending on the fuel used, compression can make a big difference as well. For a low volatility fuel like methanol, really high compressions can be reached without giving up advanced engine timing and causing pre-detonation (a condition where the fuel mixture ignites too early in the up stroke annd usually folds up a con-rod). If using gasoline, then octane levels must be drastically increased to keep a high compression engine from pre-detonating. Gasoline can get tricky as it will detontate without a spark under high cylinder pressure. Very bad condition that will literally destroy an engine.

You need to find out what the power curve of your motor is. Where it makes peak horsepower and where it makes peak torque. The objective would be to have an engine that revs to a very high horsepower number for high sustained top speed that also has stump pulling low end torque to improve acceleration. As smaller displacement engines do not have large quantities of torque, most engine builders build them as screamer engines with a high horsepower number that requires a lot of close set ratio gears to keep the kettle boiling. This usually equates to a high maintenance engine that is expensive to maintain. A higher torque motor with a lower peak horsepower and lower rev limit will generally last longer, but requires a different driving style and strategy. This is essentially what Peugeot did with their new 307 world rally car. It uses only a four speed gearbox because it makes so much more torque.

[avsfan733]

order of payoff: (as far as im concerned)
compression
cams
internal lightening (rods pistons crankshaft)
porting
blueprinting (sometimes includes above)

also look other places besides the engine such as the transmission flywheel (the lighter the better unti la certain point) and just straight up tuning of the engine such as fuel air and ignition but those are prolly obvious ones

[GTV27]

A cheap change to save a couple (?) of horsepower is to ditch the alternator and run a total loss ignition.

If this is not acceptable (? rules?) then go for the lowest output alternator that you can get hold of to reduce friction/drag on the engine.

[Onlooker]

And make sure that the belt snaps as soon as you pull out of pitlane.You can hook up a switch that turns it off from the dash,equally you can get a data logger to turn it on and off depending on what G's that the car is pulling,ie accelerating = no alternator,braking = full alternator, and above say 100mph = working. Or hook it up to your brake light switch so that it only works when you have your foot on the brake

[zefarelly]

electric water pump, oil pump to reduce whats slaved off the engine ? and make cooling/lubrication more efficient so you can thrash it more !

[KC]

A popular item among today's version of hot rodders is to use gear reduction pulleys on engine driven items such as the water pump, alternator/generator, a/c, etc. They are still there and functional but turning lsower and taking less power to run. This will work easily with a smaller and lighter alternator especially.

[Mike Holmes]

Read the regs!! they are so specific for F750 most of the above is irrelevant, you can't change the cam, fit electric water pumps, polish etc on the Fiat Engine.

[imull]

thats what I though Mike. Asked about at uni today and the people who are involved with it have all said that they are sticking with Reliant engines...

[Mike Holmes]

I used to race a Jeffrey and then a Marrow in F750, the biggest headache was the Reliant engine, when you had a good one it went like stink but not for very long!! In the end the frustration became too much so I went to Race a MG Midget, at least now I have every expectation of seeing the chequered flag at the end of the race. Having said that they are brilliant little cars and if you want to learn about setting up a car and changing suspension it's great.

[NickReeve]

Personally I'd think that if you're a novice racer with a good handle on suspension and chassis settings I'd be inclined to do as little as possible with the engine other than build it as bulletproof as the regs allow. Classic case of 'to finish first, you must first finish'. Build for reliability and longevity and keep as much of that torque as you can as well. Concentrate on outhandling and outbraking 'em.......!

[Red Dog]

Ntrprise,

You are very restricted on mods to the Fiat as has been mentioned. You can:- lighten the flywheel, fit your own inlet and exhaust manifold, raise the compression, alter the cam timing but not the profile or lift, alter the ignition timing, run any carb but use only one choke, and very little else.

It might interest you to know that two of the Fiat engines running at the front last season were more standard than if you did the above listed mods. Do the manifold, compression and flywheel mods then get it running at its best with very careful building and setting up. Concentrate on getting the car to handle and then leave it alone until you are in the top 8 or 10 every time.

Best of luck. See you at the track.

[KC]

Since you are so limited in modification, you might look into disassembling the engine and having all the components internally balanced. Most racing engines in the US do not use a high mass flywheel or torque converter and the engine parts are all balanced down to one gram to keep them from adverse vibration. It can do wonders for smoothing down the engine and making it last longer.

[NickReeve]

Originally posted by Red Dog
Ntrprise,

You are very restricted on mods to the Fiat as has been mentioned. You can:- lighten the flywheel, fit your own inlet and exhaust manifold, raise the compression, alter the cam timing but not the profile or lift, alter the ignition timing, run any carb but use only one choke, and very little else.

It might interest you to know that two of the Fiat engines running at the front last season were more standard than if you did the above listed mods. Do the manifold, compression and flywheel mods then get it running at its best with very careful building and setting up. Concentrate on getting the car to handle and then leave it alone until you are in the top 8 or 10 every time.

Best of luck. See you at the track.

Spot on! I suspect that careful building is the key. No mass produced engine is ever built to optimise its theoretical performance so any gain you get is for free. I agree with KC on balancing IF its allowed......

[Red Dog]

Cheers Nick!

Balancing is allowed but one rod/piston must remain untouched and the crank must not be lightened.

The Fiat has a good bit more low down torque than the Reliant but it amazing how similar the performance of both engines is in terms of lap time. The biggest gain for Fiat runners is the reliability, as the Reliant is a bit fragile at 9000 rpm!!

The reliability thing is so important, especially for new drivers. Every problem you have (and there can be so many) weighs you down more and more and stops you developing as a driver.

Having been through the learning curve over the last 4 years I would urge any newcomer to focus on the basics and not be distracted by tweaks - especially of the demon kind.

[NickReeve]

Originally posted by Red Dog
Cheers Nick!

Balancing is allowed but one rod/piston must remain untouched and the crank must not be lightened.

Oh - sneaky! So no lightening the rods to 'balance them'!
Back to the old Prod saloon days almost, where you had to dig around the parts bins until you found four rods that were as light as possible and as close together in weight as possible. Obviously then its a question of selecting the lightest piston/rod combination then balancing down to that one. Assuming the crank is cast iron (or is it a forging?) can you debur the casting marks without being accused of lightening it?

[Cameron Winton]

A bit of lateral thinking. If your allowable modifications are limited how about reducing weight? It is often viewed as free power. Look everywhere. The biggest single item in the car in terms of weight, sometimes after the driver, is the engine so removing absolutely everything not necessary (eg grinding off redundant lugs etc)eventually all adds up.
I have also heard of drivers dieting before a season starts when competing in low power cars.
Everything counts. I heard an urban myth type story from 1960's dinghy sailing where an ultra competitive crew refused to paint their boat red because it contained lead!

[reddy]

Good comment about the weight. I used to be umncompetitive and about 90kg lost 10kg and went signifigantly faster.

the best thing to do is to buy about 3 engines. pull them all apart. Find the lightest rod thqt you can, and use that as your template. Balance them so that the big ands and the little ends weigh the same relative to each other... And you can also make sure that when you build the engine to use old oil compression rings to keep the friction down. Buy a quality dial gauge and make sure you are getting the maximum valve lift that you can. You may need to reshape the tappet end for example.. Make sure you have the latest 5 angle valve cut. geez, this reminds me of the old days. (If your really sneaking and have a good machine shop you can also look at have an offset crank....)

good luck and don't be surprised if it takes a few motors to build a good one..

[BSTR]

Originally posted by Cameron Winton
...
I have also heard of drivers dieting before a season starts when competing in low power cars.
...

From January 1st until now -8 kg and still atleast 7 kg to go until first race of the season... It's a lot easier to loose fat than cutting ends of all the bolts in the car or pay huge amounts of money for some 100 grams lighter battery boxes etc.

[zefarelly]

good point reddy . . .Ive not built loads of car engines, but when I used to build 2 stroke Lambretta engines you'd do the same thing again and again with fairly accurate consistency, 2 would be good, 1 would be poor, and one would fly . . . .if only for about 4-5000 miles before it went bang !

[imull]

Originally posted by Cameron Winton


I heard an urban myth type story from 1960's dinghy sailing where an ultra competitive crew refused to paint their boat red because it contained lead!

One of the blokes I sail with was disqualified from one tournament when he turned up with a boat that had been sanded back to the gel coat.

Also the top class Lasers have a hugely thicker centreline on the hull built up in legal materials and a really thin and flimsy deck. The rules say that the total hull weight must be, now where the weight must be...

Stewart Grand Prix also painted their cars white as it was the lightest colour.

What do your wheels weigh. There are some very light wheels on the market that will ultimately improve handling through lower sprung (or is it unsprung. can never remember )weight

[GTV27]

Wheels are unsprung, body is sprung.

Wheel weight saving is especially worthwhile as it benefits overall weight (always good), unsprung weight (good for suspension efficiency) and rotational inertia (good for braking and acceleration performance).

Also don't forget the tyres when considering wheel weight.

[imull]

cheers gtv. always get the mixed up, just like my left and right

[mark ch]

Check your regs as to what is allowed

http://www.motorsnippets.com/750mc/r...nship_2004.pdf