depends on the quality of the parts and whether the lump actually makes 156bhp to begin with.
get top stuff and a really decent headwork, with the right fuelling you could get to 170.
if its off the shelf tat then 160 is more likely

 

i agree

 

Bill Blydenstein recons 15% on an XE - that is already 179bhp - with a manifold that would be a bit higher - so 180 could be right, but it really would have to be extremely top spec work.

 

15% I thought it was difficult to improve on the standard XE head, let alone a 15% improvement.

 

it's not difficult - there's a tonne of things that can be done to improve things - but they're all quite small on their own - there's no one thing that gives huge gains.

I'd still like to see the engine which has only headwork actually make a genuine 156bhp + 15% though, not convinced about that at all.

 

would it not need the fuelling fettled a touch as well?

 

Bill B claims 15% for the 8v heads and about 8% for the 16v heads. That's at the wheels too, so it's about 14BHP on a 2.0 8v and about 10BHP on a 16v head.

 

and a lovely amount of mid-range too.

god knows how much he'll charge for the b+ pack on a 16v head though

 

10% at best is much more like it.

 

Depends on the car, There have been plenty of C20XE engined cars rolling roaded which have been standard and come out with a much higher bhp than the standard 150/156 figures.

 

Depends on the car, There have been plenty of C20XE engined cars rolling roaded which have been standard and come out with a much higher bhp than the standard 150/156 figures.

Rolling roads are as good an indicator of power output in some cases as the bbcs weather forecasting abilities lmao

 

How else are we supposed to measure bhp?

 

guess and then add 10

 

Good Plan,

 

Remove engine, with loom + ECU, and exhaust system complete, and put on a pukka dyno...

accurate flywheel figures!

Quick edit: It's about time we all just quoted wheel figures, they are a lot more important than flywheel figures, and are usually fairly accurate.

 

but then we have a problem Brian because we can't accurately calculate gains against std factory power figures.

 

Aren't 1/4 miles a good indicator if you know the weight of the car, the you can work out the power??

 

have you not seen the 6 page nova valver thread? lmao lmao

very interesting car your building by the way.

 

It's about time we all just quoted wheel figures, they are a lot more important than flywheel figures, and are usually fairly accurate.

i used to think that too until a pretty eye opening diatribe from sir dave of andrews.

In brief it said rolling roads produces unnatural compression of the tyre wall. The tyres sit in the crutch of two rollers; out on the road you only have one contact patch. Then you have straps or lardy blokes sitting on the slam panel. Transmission losses are increased exponentially.

You NEED coast down losses to add back to the wheel figure, coast down losses are the most accurate way of measuring the whole drive train, tyres and friction. Some people say coast down losses are bunkum, clutch could be dragging, tyres could be below normal pressure, but it doesn’t matter because the losses incurred during the power run will be EXACTLY the same as the losses incurred during coast down, that’s the whole point.

 

, but it doesn’t matter because the losses incurred during the power run will be EXACTLY the same as the losses incurred during coast down, that’s the whole point.

But they're not. In one case the engine is putting load through the gearbox and there are losses. In the other case the inertia of the dyno rollers is putting load on the gearbox. It's not the same, though it does give a rough estimate of flywheel power.

Acceleration increments are the most meaningful tests.
Wheel power figures give you some idea.
There are no reliable ways of measuring power, but any dyno run with wheel and flywheel (from coastdown) losses will give a good idea.
Just don't expect the results to be better than +/-5% accurate.

Best use of a dyno is in looking for problems or effect of changes.

 

have you not seen the 6 page nova valver thread? lmao lmao

very interesting car your building by the way.

I must be wrong in the head, I should probably just dump in a LET, being different is good though

 

Quote:

Just don't expect the results to be better than +/-5% accurate

Jusy incase anyone missed it.

Dan

 

heres the tech document written by dave walker, that dave ndrews was quoting.

Having a pair of rollers pressing against the road wheels really does introduce some unrealistic losses into the picture; in that you have an unnatural degree of compression of the tyre wall brought about by a relatively small diameter roller. What's more you have two contact patches giving double the loss. If the operator is really keen and puts a strap on the back of the car to pull it down onto the rollers it gets really interesting! If a car needs that level of grip it generally has a very powerful engine which in turn means big, (wide) tyres. The bigger/wider the
tyre then generally the more energy it takes to compress the side-wall. All basic stuff.
You don't have to be a genius to work out that the faster you go, the more effort it takes to keep deforming the side-wall (same deflection but in an increasingly smaller time-frame) hence "total rolling losses" increase with road speed.
Where it gets interesting is in the way you set the rolling road up. On my Sun RAM12 it has the facility for holding a given road speed - regardless of engine applied load. Straight forward, you dial in the road speed and when the car gets to, for example, 60mph, it won't go any faster. You can increase throttle until the tyres spin and smoke, but the brake holds the rollers at 60mph - regardless of what gear you are in. This is very useful for mapping - where you need to hold a steady load and speed to play with the fuel and ignition settings. On my rollers I have a digital read-out which goes to 0.1 of a bhp. When you tweak the timing on the lap-top you can see small changes which, while not deadly accurate, do give you an indication of what's going
on.

Taking a power curve is a different story. Steady state running is not the way to do it on a rolling road. For an acceleration run you need a computer with software that captures the torque at a given sample rate - usually based on roller (mph) speed. You drive against the roller in one gear, from low revs to maximum, and the computer records the load and speed - obviously calculating the bhp from these numbers. This is not as simple as it sounds.
On the front of my machine I have three dials. These allow me to adjust the rollers for simulated load. I can dial in the weight of the vehicle, the power needed to overcome wind resistance (at 55mph) and the rolling resistance (again at 55mph). This allows you to accurately simulate road conditions for fuel consumption tests. If you think I go to all that trouble for a single power run you are sadly mistaken!
There are a lot of reasons why a rolling road is not as accurate as an engine dyno. One of them is that the power of the engine is constantly changing. As combustion chambers heat up, power fades. As oil and water temperature changes, the power coming off the flywheel also changes. If you are involved in accurate research you have to carefully monitor all these parameters. I'm not. I don't.
What I have done is adjust the rolling road acceleration rate to give me a very close approximation of known cars. Example: I had a BMW showing 177bhp on the Magnex (of exhaust pipe fame) inertia roller. This machine is pretty accurate since it's just a lump of mass and a computer calculates the work done in accelerating, and decelerating, it. The computer doesn't know where the power is coming from, it's just work done - or undone. On my rollers I got exactly the same figure from that same car, in both cases corrected for standard temperature and air pressure.
For cars making between 130 and 200 bhp it seems to give realistic numbers and it's repeatable to within a brake or two, given the limitations of the system and the changes in actual power between runs. For smaller engines, like a full race 2CV, I have to increase the acceleration rate of the rollers, otherwise it could take all day to get to maximum rpm! On big 300 bhp V8 engines they woosh up so fast you can't be sure it isn't wheel-spin.
For these I increase the roller load to slow everything down. I have to admit there's an element of "feel" to it. We've done over 5000 power runs now and I think I can tell when it's all over too soon - or not.
What you get from all this is a power figure at the wheels across the rev range - totally meaningless, and here's why: The rolling resistance of the tyres depends on road speed. If I run the car up in third gear the road speed reaches maybe 90mph. If I run it in fourth gear the rollers might make 120 mph. In third I have less power loss through the wheels than I have in fourth gear, which means that in third (at for example, 6000rpm) I have 80bhp at the wheels. At 6000rpm in fourth I have only 70bhp at the wheels. That missing 10 bhp is being lost in the road wheels rotating at 120 mph instead of 90 mph.
The clever bit is measuring the rolling losses on the run down and adding these to the "at-the-wheels" figure. I can run in any gear and get the same power curve - but only after the rolling losses have been measured and added to the wheel figure. If I look at the road wheel power in different gears at the same rpm I get a totally different reading.
To prove the point we ran a Golf GTi at 3000rpm and recorded the power at the wheels. I then put another 10psi into the tyres. This higher pressure reduces the amount of distortion of the side-wall and hence reduces the rolling losses. We "gained" nearly 5 bhp at the wheels. Moral: if you want more power at the wheels, or improved fuel consumption, keep your tyres up to pressure. From this you can see that the idea of calculating a transmission loss common to all cars is patent nonsense - you need to know the road speed, the tyre size and its rolling resistance. If you get big variations at the wheels from week-on-week tests then you may well have been very careless with your tyre pressures.
From my limited experience the major loss is the tyres. If I dip the clutch and keep the car in gear while I measure coast down losses I get some added drag - possibly from the gear oil in the box but more likely due to the clutch dragging plus the load on the release bearing. To state that you get a given percentage (I think it was something like 15% or 17%) only shows a total ignorance of how the whole thing works. No shame in that. I used to happily measure power at the wheels and quote it in features - because I was ignorant of exactly what I was measuring. Ignorance isn't stupidity - it's just a case of not knowing what you are talking about.
Where ignorance becomes dangerous is when you set yourself up as a "professional" and present your ignorance to the world as proven fact. I do not claim that my rolling road gives deadly accurate flywheel figures, but it does give a repeatable number that bears some relationship to the real world.
In a contest to get the most power at the wheels I would run my car in first gear with 60 psi in skinny tyres fitted to bicycle rims. Does that make the engine more powerful?

 

i used to think that too until a pretty eye opening diatribe from sir dave of andrews.

Don't supose you have that diatribe lying around do you odders?? that would be cool
EDIT: Yeah, d'oh! didn't see your post above!

I know about the two contact patches, and fair enough, but I'd like to see the rest of that text if possible....

Coast downs always seem to be, well, innacurate. If they weren't, pumping up you tyre pressures should have no effect on the end result, but it does!

 

you pump your tyres up, you get less rolling drag on the way up, and the way down, its equal.

p.s thats the whole article from dave walker, the post just had a quick intro fom dave andrews

I've re-printed below a document produced by Dave Walker of Emerald and Car and Car Conversions, it sets out why at the wheels figures are useless as direct comparisons and why you need the RR to measure the losses by running a coast down test and adding the losses back...