Modified Power-to-Weight

[biturbo228]

So, in the vein of lightweighting and general modification, I've been putting together a geeky spreadsheet comparing power-to-weight and estimated power-to-drag of various cars, including modified ones where I can get the info. Thought I'd ask here to see if I can add anything to it

It's a bit of a work in progress, but once it's done I hope to do a bit of a comparison against 1/4 mile times to see where things shake out re: power-to-weight vs drag, and then see where some modified things stack up against production cars (basically, this all stemmed from me getting chopped by a Mk1 Focus ST and wondering how much power I needed to stop that happening again!).

So, who's weighed their car, has a decent idea of how much power it's making, and can remember what mods they've done? If you want to, I'll add it to the list and see where it shakes out other useful bits are any aero mods and/or if it's been lowered, by how much.

Will post a link to the list when I get home

[sonus]

My TVR has 106rwhp and 136fwhp and managed 192kmh in 4th at approximately 5250-5500rpm on the Autobahn and weighs 950kg

[biturbo228]

Very nice Rover V8?

At 143bhp/ton it should be sitting around E30 325i, Austin Healey 100S and my old V6 Alfa 156 in terms of speediness up to around 60-70 or so when aero drag really starts to add up. At that point, I'd expect the Alfa and E30 to start pulling ahead as their power-to-drag is better, but yours should comfortably pull past the big Healey.

Also, your Vixen being so small shows how important a small frontal area is. Despite the Alfa having a much slipperier shape (0.31 drag coefficient), because it's so much bigger it produces about the same drag as your TVR (if your TVR is lowered at all it might be even better!).

Neat

[Frankenhealey]

The Frankenealey when running quad Weber 48DCOEs was 484 fwhp and 1020 kilos. At 140ish the front end would lift. Standing 1/4 at the Jersey Festival gave 12.19 and 122mph on road tyres.

[biturbo228]

Jesus. 'Frankenhealey' is definitely an apt name. Near as damnit the same power-to-weight ratio as a Ferrari Enzo! It'll out-drag you eventually, but you'll scare the living daylights out of it until that point.

Drag-wise, if the estimations are about right (there's a bit of error creeping in around frontal area and some drag coefficients), you could roll on the throttle at 70ish next to a Dodge Challenger SRT8 392 (or a super-slippery Audi B9 S4) and match speeds with them all the way up. If you tried that from a standing start you'd mince them

[colnerov]

Final drive ratio plays a part. Acceleration vs top speed.

[scimjim]

And gear ratios, tyre/wheel size and torque characteristics.

[stealthstylz]

And which wheels the engine is turning. I helped build a 650bhp MK4 Astra years ago, ran 12s in the 1/4 mile but would outrun anything we ever came across on the road from a rolling start. Can't remember the exact times now but 100-180mph was faster than any supercar you could buy at the time.

[biturbo228]

Absolutely, and drivetrain losses and power under the curve (which is what it really is when an engine is 'torquey').

Good old lying about power figures is a good one as well. I've had to leave out quite a few older American cars, a fair few Japanese ones, and some of the older Brits where I haven't been able to get good net power figures for them. It's interesting how much it can vary.

For instance, early PI TR6s state 150bhp, but are hovering around 141bhp at the flywheel, and the 240Z's 151bhp is more like 135. Found that out when I was wondering why the 137bhp MGB GT V8 was as quick or quicker than both. Turns out MG was telling the truth and the other two were telling fibs

[Frankenhealey]

Sept 19, 2019 11:20:38 GMT biturbo228 said:

Jesus. 'Frankenhealey' is definitely an apt name. Near as damnit the same power-to-weight ratio as a Ferrari Enzo! It'll out-drag you eventually, but you'll scare the living daylights out of it until that point.

Drag-wise, if the estimations are about right (there's a bit of error creeping in around frontal area and some drag coefficients), you could roll on the throttle at 70ish next to a Dodge Challenger SRT8 392 (or a super-slippery Audi B9 S4) and match speeds with them all the way up. If you tried that from a standing start you'd mince them

Note the road tyres point, RWD and 7J back wheels. Anyhoo it's back to approx 440 bhp on a 4-barrel now as 8mpg on the Webers was too wallet threatening.

[mungo]

my bug is 180 hp and did the 1/4 in 13.05 @99mph.
probably weighs 850kg
2332 with 48IDA's

[biturbo228]

Sept 19, 2019 12:22:00 GMT Frankenhealey said:

Note the road tyres point, RWD and 7J back wheels. Anyhoo it's back to approx 440 bhp on a 4-barrel now as 8mpg on the Webers was too wallet threatening.

'Only' 440bhp but don't blame you for the 8mpg part...

Sept 19, 2019 12:38:45 GMT mungo said:

my bug is 180 hp and did the 1/4 in 13.05 @99mph.
probably weighs 850kg
2332 with 48IDA's

Neat that's pretty quick! Looks lowered by the picture, any idea how much by? Makes quite a bit of difference to the drag.

[mungo]

The rear is stock and the front is down probably 6 inches from stock .
235/60 15 M&H racemasters on the back
From a standing start it has so much grip.......... it's never lifted the front wheels though, might have done with full slicks.I could never afford to start breaking stuff so retired from the strip.

[biturbo228]

Gotcha I've averaged it to 3" drop between front and rear. With that, you're sitting around 964 Carrera RS' and CLK55 AMGs

The beetle's drag coefficient is as you'd expect for a 50s design though, so in terms of top speed and acceleration above 70 or so you're looking closer to a Mk2 Golf GTi 16v. Seems quite similar to a lot of hopped up older cars: scares the daylights out of things at stop-lights, but on a mile drag strip they'd get left behind.

[Frankenhealey]

I once entertained starting a 1/2K-NASP club, i.e. 500bhp/ton naturally aspirated. No turbos, no chargers, no NOS. It would have been a small group.

[stealthstylz]

Sept 19, 2019 12:10:19 GMT biturbo228 said:

Absolutely, and drivetrain losses and power under the curve (which is what it really is when an engine is 'torquey').

Good old lying about power figures is a good one as well. I've had to leave out quite a few older American cars, a fair few Japanese ones, and some of the older Brits where I haven't been able to get good net power figures for them. It's interesting how much it can vary.

For instance, early PI TR6s state 150bhp, but are hovering around 141bhp at the flywheel, and the 240Z's 151bhp is more like 135. Found that out when I was wondering why the 137bhp MGB GT V8 was as quick or quicker than both. Turns out MG was telling the truth and the other two were telling fibs

Think a lot of it was whether it was tested to DIN standard or SAE or whatever. I know the Yank stuff was over rated compared to as it was in the car as they didn't test then with any of the other spinny bits that are related to the engine other than that what is needed for it to run etc. However some stuff was then massaged up or down further by sales people, for insurance or racing reasons usually.

[sonus]

Sept 19, 2019 9:03:07 GMT biturbo228 said:

Very nice Rover V8?

At 143bhp/ton it should be sitting around E30 325i, Austin Healey 100S and my old V6 Alfa 156 in terms of speediness up to around 60-70 or so when aero drag really starts to add up. At that point, I'd expect the Alfa and E30 to start pulling ahead as their power-to-drag is better, but yours should comfortably pull past the big Healey.

Also, your Vixen being so small shows how important a small frontal area is. Despite the Alfa having a much slipperier shape (0.31 drag coefficient), because it's so much bigger it produces about the same drag as your TVR (if your TVR is lowered at all it might be even better!).

Neat

IT has a Daimler 2.5 Hemi V8 that was rated at 140bhp from the factory fitted in the Daimler 250 V8 saloon. 195/65/15 tires, Jaguar e-type 3.31:1 diff and BorgWarner T5 gearbox.

[austinpowers]

I don’t think my Trabant is going to scare any Farriers, but the engine has been modified from 26hp to 43hp.
And is now just below 600 kg.

[mk2cossie]

My ole girl weighed 1420kg, and managed a quarter mile of 15.8seconds with 175bhp at the flywheel.

Now makes 207bhp at the flywheel, but not been back to Santa Pod yet to see what improvements have been made!
Probably lowered about an inch from standard at a guess if that helps

[mungo]

Sept 19, 2019 14:35:58 GMT biturbo228 said:

Gotcha I've averaged it to 3" drop between front and rear. With that, you're sitting around 964 Carrera RS' and CLK55 AMGs

The beetle's drag coefficient is as you'd expect for a 50s design though, so in terms of top speed and acceleration above 70 or so you're looking closer to a Mk2 Golf GTi 16v. Seems quite similar to a lot of hopped up older cars: scares the daylights out of things at stop-lights, but on a mile drag strip they'd get left behind.

 yeah, I'm out of legs at the end of a 1/4 mile let alone a full mile !!  and I'd deffo not want to be anywhere near the thing over 100 mph ....it's a deathtrap   (no seatbelts! )