Power

Message

2F45T4U · #1 Post by **2F45T4U** » Mon Oct 09, 2006 2:17 am

Can you get this much power out of a Sprint engine? Surely 240hp at the wheels would mean about 300 at the flywheel!?

http://cgi.ebay.co.uk/TR7-16-Valve-TRAC ... dZViewItem

Lewis · #2 Post by **Lewis** » Mon Oct 09, 2006 8:06 am

That's Marks from Jigsaws old TR7 racing car - going by the photos. A tad optimistic is the power figure, methinks.

240 at the fly would be more likely.....IIRC that was the kind of power he quoted for it, wether that was hideously optimistic or not

I've seeen another Sprint engine running over 240BHP but that was with a healthy dose of laughing gas

#3 Post by **Mad Mart** » Mon Oct 09, 2006 8:17 am

I'm sure Scott can tell you as he drove it round Mallory. It's more like 220bhp @ the flywheel IIRC.

xvivalve · #4 Post by **xvivalve** » Mon Oct 09, 2006 9:30 am

There was an 'interesting' comparison between Mark's figures for Scott's car and what Aldon managed to get out of it...

Dollyboy · #5 Post by **Dollyboy** » Mon Oct 09, 2006 12:32 pm

I thought BHP was the 'engine braking corrected' figure, therefore not 240hp at wheels, but a theoretical 240hp at flywheel accounting for drivetrain losses?

Lewis · #6 Post by **Lewis** » Mon Oct 09, 2006 12:49 pm

You're right there Dollyboy! You could work out the BHP of the engine on a rolling road, without transmission losses (but it would not be very accurate!)

What follows is a public service announcment!

BHP (Brake horsepower) actually refers to the power measured at the crankshaft using a braking system brake - an engine dynometer. It used to be that engine power was measured using the deflection resulting from this braking being applied - nowadays it refers to the braking system that is used to measure torque during the run, which can then be used to calulate power afterwards (multiply the torque by engine speed in revs per second and then by the circumference of the braking band to give the power)

Rear wheel horsepower is the measure of what the car is actually delivering to the wheels (or wheel horsepower, for 4 wheel drive vehicles and front wheel drives). This is measured on a rolling road and accounts for the all the losses resulting from ancilleries such as air conditioning, the alternator and of course the transmission losses from gearbox and axle.

The two primary US measurements were gross and net horsepower. Net is now the common one.

Gross horsepower is the now outdated power measurement at the crankshaft without any ancilleries - anything driven by the engine that's not absolutely essential - such as alternators, power steering pumps and with the fuelling and ignition system in 'ideal' configuration.

Prior to 1973, horsepower specifications were listed by the manufacturers as gross horsepower. After 1972, manufacturers provided net horsepower specifications as they were more reflective on the actual outputs of the engine. Net horsepower is the same concept (power measured at the crankshaft) but includes the losses of all the ancilleries - these are both effectively the same as BHP...

I bet they'd be disappointed if they rolling roaded that TR7

- Then again, it may well be 240 at the crank....

Drivetrain losses are usually in the region of about 10 to 25%, can be more for complicated powertrains such as the Imprezas 4x4 system and so on.

Shorty's shaker Fordson was a devil of a machine and that probably could make 300BHP......but it was made to take half that in N20

2.1 triumph dolomite sprint engine full race spec with new block lightened & balenced bottom end with steel rods,1 off JE racing pistons machined in the states,comp head 3 angle valve seats, 306 duration piper cam,twin 45 webbers with K&N filters,msd blaster coil,moroso leads,msd digital6 ignition system,NOS fogger kit with 75bhp jets at mo but engine built to take 150bhp

Was a fast maachiiiiinneeee!

Judge Mental · #7 Post by **Judge Mental** » Tue Oct 10, 2006 9:18 pm

All I can say is that it seemed to rev alot more freely than mine. The 240bhp figure was what it achieved on Baldwin's rollers. His figure is a guestimated flywheel corrected, not at the wheels. Mine was 220bhp on the same rollers and has now been more or less confirmed as being 165rwbhp so I would hazard a guess that the tr7 engine produces 200 at the flywheel. It felt about right for that.

My cerbera was around 300 bhp per tonne and that was alot faster than this TR7. I think Mark sold it for £2350 last year. I think Martin saw the last owner having problems with it at a track day.

#8 Post by **Mad Mart** » Tue Oct 10, 2006 9:21 pm

I think Martin saw the last owner having problems with it at a track day.

Aye, Mallory last April, but can't remember what was wrong only that he didn't get much track time.

These were taken at Mallory in April '05.