DaveK

Now you've got me worried because I didn't check the price.....

Their website says a straight power test is £55 which seemed like a bargain, so I booked. But why would you need 12 cars for a shootout? Couldn't you just turn up with however many and pay £5 extra each? Or is their website out of date and this is going to cost me £££££? (in which case I'll cancel!).

LouZ

I had my '90 C2 Tip tested on a "Mustang" Dyno in May as part of our PCA club's - Dyno Day. This is a 4-wheel Dyno, so a lot of C4 owners ran.

The shop stated that they extrapolate flywheel Horsepower by applying a multiplier to the rear-wheel (or 4-wheel) horsepower figures.

The factors used were:

1.28 multiplier for a C4 manual
1.18 for a C2 manual
1.25 for a C2 Tip

My measured rear wheel horsepower was 207.3 RWHP which would extrapolate to 259 engine HP.

A C4 with some mods put out 208 RWHP, then a custom primary bypass was fabricated and installed. The C4 retested at 217 RWHP.

These figures fall in line with Christer's results.

Do a search in early May 2003 for the various results.

Christer

I make 216rwhp about 254.1fwhp at 15% loss. I think JZ's dyno showed 207rwhp as 237 or something....

In any case, it really doesn't matter what the fwhp is - it is the whp that counts. So I think around 210rwhp is about the mean - you have a rebuilt engine and bypass or whatever so that's about right!

Dave. I can't make Monday as I am in Cornwall. I don't suppose I will do another one until I make further changes anyway.....

Phil Raby

Dave,

For some reason my reply to this didn't appear. Basically, I wasn't paying so am not sure of the price. I thought he said £80 an hour. Be worth checking.

Cheers

Phil

DaveK

Just checked - it is as per website, £55 + vat (so £65 basically). Hardly more than a tank of petol so well worth it.

Gavin

I have used the JZ Machtech Dyno on a number of occassions with different cars. Their cautiousness, if it exists, appears to be in the losses quoted, which are around the 25bhp figure. I think this gives a more realistic idea of what power the engine is actually giving. I thought all the dyno operators these days gave you rear wheel HP and the corrected Flywheel equivalent.

My C2 gave 262bhp at rearwheels after being rebuilt. It is still a bit tight and is due an upgrade to the latter plastic type manifold and enlarged throttle body & re-chip (waiting to be fitted). This according to Steve at JZ should get me about another 10 horsepower (along with the engine bedding in a bit more) and push me to within a 'gnats wotsit' of the magical 300bhp figure.

Christer

Gavin

262rwhp equates to around 308fwhp - that sounds way high unless they put some mods in it while they were there!!

The losses do not equate to a fixed figure like 25bhp - it is generally considered to be a percentage loss.

At JZM, they do not have a fixed value for the losses they use a formula.

Most cars are in the 207-215rwhp range when standard - how did you get 262rwhp just by rebuilding the engine? I think something is wrong somewhere. Can you check your figures? Did you get a 3.8 conversion done at the same time?

johnfm

What gear did they use for the dyno run - 3rd or 4th? DId they give you a graph?? Post it !

Gavin

Sorry, I was talking from my own personal experience of their dynoplots. I understand that they do not just apply a fixed figure when calculating flywheel bhp, but in my experience the actual loss figure has tended to be around the 25BHP figure. For example my old 3.2 had a loss figure of 22BHP. The subject of flywheel BHP against rear wheel BHP appears to be one that runs and runs. However, I don't think it is as simple as just using a fixed % (such as 15%) to work it out. The problem with that is that the losses do not necessarily increase inline with any given increase in power.

For example, the losses shown prior to the latest mods to the engine were approx 25bhp and after the rebuild and power increase, the losses have remained at 25BHP. Just because the engine may have gained 10% in power, should the losses have increased by 10% ??

I would be interested in any comments as this only my understanding as an enthusiast.

This is the current spec of my car after a top end rebuild at JZM:

- Titanium Valve spring retainers
- New valve springs
- Re-conditioned fuel injectors
- Roock/Porsche Sports cams ( Ask Steve at JZM for Spec)
- Raised Compression ratio
- Cup Air box
- K & N air filter
- Cup Bypass Pipe
- De- cat
- Re-chip
- RS flywheel and clutch
- RS Brakes, Full Roock Suspension and Strut Brace

The figures of 262bhp @ rear wheels and 288 @ Flywheel are as shown on the print out and graph. I believe that the run was in 4th, but i'll have to check as this is from memory. At the moment I do not have the ability to post the graph, but will when I can.

I did consider a 3.8 conversion at the time, but concluded that for the money the gains were not that great.

I'll keep you advised of any progress, or lack of it, thro the change to later inlet manifold etc.

robmug

Phil

I'd be up for the £50 shootout! What's the cost of their 'normal' RR session in comparison?

As an aside, I once had my E36 M3 Evolution superchipped (I was there on business and it seemed rude not to!) - power went from 321 to 341 bhp. On the way home I was trying to find where they had moved the rev limiter to - after 7000rpm in 3rd (about 115 mph) I gave them a call, to be told that they had removed the rev limiter...I must have been only a few rpm from blowing the engine I guess...

tonytaylor

Someone give Gavin the G-tech - it would be interesting to see what his car does with that.
262rwhp doesn`t really match up to 288 at flywheel.

DaveK

Rob,
As I posted - normal RR session is £55 + vat, so basically £65.

This is actually quite a bit cheaper than I had thought RR sessions would be - and they are 4WD dynos so I can go.

Gavin

Out of interest, there is a 3.8l Roock conversion around which I am sure some of you are familiar with, ( as featured in 911 & Porsche World, Michael Hinchcliffe's car). Power figures are:

- 280.2 BHP at rear wheels
- 304.8 BHP at rear wheels

Power loss 25bhp.......

JZM dyno......

Phil Raby

Hi Gavin

That was a nice car

I assume you mean 'at the flywheel' for the second figure?

Cheers

Phil

Gavin

Sorry, yes I do. I was /am watching 'ultimate force' on the tv...!