BHP to 0-60 time, Is there a formula?

[Big Brother]

Anyone know a formula to work out how many bhp I will need to get a certain 0-60 time.

 

Currently car is a flared (sexy) winged, aeroscreened, 135 bhp Supersprint crossflow (118bhp according to Roger King)

0-60 time is quoted as 5.6 seconds (managed close this at the Brooklands day - 5.8s according to the black box)

 

Car is fitted with a 2000E gearbox with the following ratios

 

1 - 2.972

2 - 2.396

3 - 1.937

4 - 1.00

 

It also has astandard ford axle, I think its either a 3.89:1 or a 3.54:1 (probably the later)

 

Any idea how many horsepower I will need to get ...say....4.5s - 0 to 60 mph?

Also will aerodynamics play a big part on the way to 60mph?

 

 

Steve

 

www.Se7en-Up.co.uk

 

[Alex Birtwisle]

I would guess the number of pies you eat per day would have to be a factor too (sorry not a comment of any technical merit) but surely the mass of the car is important when considering a bhp/accelteration formula as well as perfect traction?

 

Alex

 

 

 

Edited by - abirtwisle on 2 Aug 2002 22:31:55

[oilyhands]

Mass, CD factor, gearing, torque profile etc.etc all these play their part. There is a program called cartest that allows you to enter the most significant of these and is eerily accurate in predicting a cars performance, it has a database of 300 or so cars and I have already set up a model for a Caterham. It also allows you to drag one car against a number of others over the qtr mile, it predicts acceleration, top speed, speeds in gear, optimum gearchange points etc.etc.

 

Oily

[Big Brother]

Oily,

If you get a spare few minutes, could you be kind enough to take a quick look at your program with the Caterham figures in it.

 

Basically what I need to know is how many BHP will I need to run a 4.5s 0-60 time.

 

also - all you people with trick crossflows - can you post your BHP and 0-60 times?

 

ADVthanksANCE

 

Steve

 

www.Se7en-Up.co.uk

 

[EFA]

Steve,

 

Wast of time as the parameters required (such as drag coef, frontal area etc) are not generally available and vary car to car.

 

For a good 0-60 you need a lowish in Seven terms) 1st gear and a 2nd gear ration which will take you cleanly beyond 60mph.

 

Tyres make a huge difference, soft road compound being OK, but A24 ACB10's or slicks (the fatter and softer the better) will gain you a massive reduction in time.

 

Is it really worth it when the acceleration which makes a differnce is 60-120mph - where driver performance is much more consistant also.

 

 

Remember that even Peter Carmichael did not manage to break the 4.5sec barrier at Brooklands on 9/9/01 - with 250bhp, ideal gear ratio's but 6" wide ACB10's!!

 

 

 

Fat Arn

Visit the K2 RUM site

See the Lotus Seven Club 4 Counties Area Website here

 

[JonP]

Hi Steve,

 

I have a formula which attempts to equate flywheel BHP to standing qtr times as follows:

 

BHP= weight in pounds/((std qtr /6.35)^3)

 

in Excel speak, so assuming you have a 1300ib car and the stding qtr is 12.7 secs you will need

 

1300/(12.7/6.35)^3 which equates to 1300/8 which is 162.5BHP...probably about right.

Obviously 1) this is not exactly what you want, and 2) makes loads of assumptions.

 

I would imagine you will need around 180BHP to achieve what you are looking for

based on my experiences, which is just achieveable with a roadable crossflow

 

BTW still reckon you would be better keeping your crossflow assuming you stay with your current car

just for originalities sake, but for real nutter blaster performance you would be better off with a more modern engine in a more modern chassis...:)

 

Cheers

 

JonP

 

Back Sevening again!

[JonP]

Steve,

 

You can tell I'm new to this lark....first smilie forget the brackets

 

JonP

[Big Brother]

Thanks all,

 

Here's the reason for the post.

 

I have a pretty early Caterham powered by a crossflow.

I was considering selling and getting a Superlight or keeping and going Zetec.

 

As several people have pointed out, the car is verging on being a classic and the crossflow is a classic Seven powerplant.

 

I have now made up my mind to stay with a 1959 designed engine in my 1957 designed car 😬

 

I want to find out the cost of getting the car to superlight (R300) performance while staying with a crossflow.

I understand that the engine/car is a fair bit heavier so I would need to better the R300's 160bhp and trim off a few pounds (car and driver )

Im just not sure how much extra BHP I will need to keep up with the "young uns"

 

Ideas....

 

 

 

Steve

 

www.Se7en-Up.co.uk

 

[murph7355]

IMO you should (if you haven't already) go and have a good blast in an SL.

 

The accelerative abilities are only a small part of the equation, and I very much doubt you'll get a XF engned car feeling the same no matter how much power you chuck at it or how much weight you can trim out.

 

I'm not saying it will feel better or worse, just significantly different.

 

So if you've not had a good stint in an SL/R300 it would be wise to. That way you'll be able to tell which bits of its personality you do and don't like.

 

Example - with the K engine and gearbox you will have a car that is much lighter in the nose (not much you'll be able to do about weight there) and is much keener to rev. Indeed which needs to be rev'd. These two traits alone will give you a huge difference in feel...

 

0-60 times are only of any worth if you're prepared to be pretty brutal with the car and have someone next to you who is prepared to do the same. I doubt any of us come close to our car's potential acceleration wise from 0 on regular occasion (as Arn intimates).

 

On the classic front, I'm not sure. There's a very strong argument for saying that the original SL, in proper SL form is likely to become one of *the* classic 7 models. The R300 dilutes the purity a bit in standard form and many state the std SL to be the best 7 ever.

 

I'm not rubbishing XF's here as I think they sound lovely and go bloody well when fettled (Excess Baggage step forward). But they're not exactly rare or anything.

 

Have a go in an SL and maybe look at getting into a used original if you like it?

[Paul Ranson]

For a good 0-60 you need a lowish in Seven terms) 1st gear and a 2nd gear ration which will take you cleanly beyond 60mph.

Probably better to have a first gear that runs to just over 60mph. You will still be able to break traction no problem. It would be a real pita on the road though.

 

Has anybody tried a 0-60 run in second?

 

Paul

[Swiss_Tony]

Paul

I used to have a 3.4 diff in my 7 which took it over 60 in 1st.

It wasnt that bad to drive on the road but it is very hard to get a decent 0-60 time. It would either light the tyres up or bog down its very difficult to get it right.

I have since re-fitted the 3.9 which is a lot more controlable.

 

James

 

[EFA]

Paul,

 

I run a setup whihc requires 2nd to get to 60mph - the result is much quicker times.

 

Without a seq box, on the less than perfect Brooklands day on 9/9/01 I did a 3.38 best and consitant 3.45's to 3.6's. Interesting to note that without the weight of a passenger the times were .4 secs higher.

 

Onto JonP's calculation, I have just reverse engineered your equation and this gives K2RUM weighing 1364 Lbs (with me in plus fuel etc) a stg 1/4 time of 9.42 seconds!!

 

Please note I recognise this is an utterly impossible time before Dave Edmunds starts interpreting this as a claim.....

 

 

 

Fat Arn

Visit the K2 RUM site

See the Lotus Seven Club 4 Counties Area Website here

 

[Big Brother]

Andy,

 

I appreciate what you are saying about the SL and the X-flow being totally different beasts.

The whole upgrade question arose when I accepted a few passanger laps in a SLR.

What struck me was the sheer acceleration difference between the two cars.

I understand the difference in cornering and braking ability, however the acceleration must be reachable, albeit not to the level obtained in a SLR due to the 190 Bhp on tap.

 

The standard SL (R300) is quoted as having a 4.7 secs with 160 Bhp.

I'm just keen to know how many gee gee's I will need to match this 0-60 time lugging a great heavy lump around....Oh, and a crossflow engine too

 

 

 

Steve

 

www.Se7en-Up.co.uk

 

[BDR750]

Trouble with 1st gears that give 60+ mph is that you often still need to change into 2nd to reach a true 60mph road speed as a result of wheelspin.

 

My car suffers from this and although geared for 62.6mph in 1st gear at 9,500 never achieves that road speed eventhough I hit the rev limiter at 9,500 rpm in 1st.

 

This is evidenced from the telemetry as the rpm in 2nd gear at the point of change is always lower than what it should be if i'd really achieved the roadspeed equivalent to 9,500 rpm in 1st.

 

Getting back to the point Steve I don't think there is a definitive formula. V8 drag racers have over the years produced drag strip dynos but their parameters are obviously not flexed far enough to cater for 1000lb machines as my times/terminal speed/weight indicate i've got less than 200bhp.

 

My only other comment is that I think you'll need a fair bit more than 162bhp to run 12.7 secs at Santa Pod in a 1300lb car.

 

Finally I wouldn't suggest taking passenger's to improve your performance 😬

 

 

 

 

[Paul D Jones]

Arnie can you please post the transpossed formule as my maths is not up to it anymore.

 

 

 

Paul.

See My Car Here

[Jason Plato]

When my superlight 1600 was in std factory spec ( 140bhp ) aeroscreen , 185/60/13 tyres , 515 kg , when myself and kevin ford - he had 150bhp crossflow , windsceen , live axle , we did a drag from 20mph side by side upto around 110 mph there was nothing in it , maybe half a car length .

 

If you are looking for similar performance to a R300 , then maybe targeting similar power/torque per ton would be best ??? . IMHO 0-60 depends on so many factors where as 20-100 mph is easier to replicate or measure .

 

Dave

[edmandsd]

It seems we're justifying why Caterham's have no advantage being lighter ??

 

Truth is the lighter the car the more significant a passenger becomes in terms of their proportion of the all up vehicle weight - This is why a motorbikes performance is reduced enormously with a passenger but not a Bentley Turbo R.

 

Weight savings are less noticeable when an object's moving than from a standing start. If Arnie had set his car up for optimum acceleration from a standing start with just himself in the car then he'd have got better times than simply compensating with a passenger.

 

 

 

Edited by - edmandsd on 4 Aug 2002 11:20:07

[cdg]

Steve

 

Are you sure about those gear ratios? Don't look correct to me. 2000E ratios are; 2.9, 2.0, 1.4, 1 (approximately)

 

Chris.

 

 

[Big Brother]

Chris,

 

I got them from the Tony Weale book.

They are for the 2821E "Bullet" box

 

Steve

 

www.Se7en-Up.co.uk

 

[Peter Carmichael]

When I was failing to achieve decent 0-60s at Brooklands I was trying to do it with a 1st gear geared to take me over 60mph. Failed as Dave explained, with the tyre slip preventing a raised 9700 hard limit from allowing >60.

 

Other attempts on the day taught me loads. Apparently you can't just dump the clutch and expect to get anywhere fast, but seeing as my clutch plates were about to wear out it seemed an appropriate expedient at the time. I am still very unsure about how to get my car off the line quickly - also demonstrated at Curborough where my 60 ft times were consistently slower than Arnie. Best 60 ft time was 2.49 seconds, IIRC.

 

*thumbup*253 bhp, up and running *thumbup*New boingy bits

[JAG]

To estimate the amount of horsepower you need for a 4.5'ish 0-60 time you should be able to simply ratio the current horsepower with the current 0-60 time.

 

This will only work if you DON'T CHANGE any other feature of the car.

 

Currently you have 0-60 in 5.6 with 135bhp therefore you should need;

 

(5.6/4.5) x 135 = 168bhp (at the same point in the rev range)

 

This is close to the R300 figure because;

 

1) gear ratios in an R300 are different.

 

2) tyre rolling radius may be different (you didn't state what your tyre size is)

 

3) manufacturers acceleration times are usually generated with a car in the optimum spec, that's not necessarily the same as the car you buy off the shelf!

 

Aerodynamics won't make much difference over such a short time but reducing frontal area can only improve things i.e.get rid of the windscreen.

 

Last point; making the car lighter will only help!

 

Edited by - JAG on 5 Aug 2002 09:18:06

[Peter Carmichael]

Too simple JAG, I would have thought. Accel from standstill has to cope with tyre slippage and you operate the car throughout the rev range and not just maximum power.

 

*thumbup*253 bhp, up and running *thumbup*New boingy bits

[JAG]

So long as the same driver is driving, the rest of the car remains unchanged (tyre type and radius, overall weight, gear ratios etc...) and power and torque maximums occur at roughly the same place in the power band then my bhp figure is about right.

 

Ultimately very few variables actually affect the rate at which a vehicle (or any other object) will accelerate or decelerate;

 

A=F/M (by re-arranging F=M.A, thanks Isaac). Where A=acceleration, F=force and M=mass.

 

So forget all the complicated bits, like tyre slippage, gear ratios, aerodynamics and power characteristics because they WON'T CHANGE.

 

The only item that will change is force (F) as that is a derivative of the engine power (and torque).

[pooh]

Surely, the more power you have, the more difficult it is to translate it into acceleration without spinning the wheels?

[JonP]

Going back to my 'magic' formula.........I think the BHP figure should be wheel BHP as there is no correction for transmission loss etc.

 

Does that make it any closer to reality Arnie??

 

Cheers

 

JonP

 

Back Sevening again!