Rear wheel horsepower, How much should I have Options

[porschefile2010]

So, we finally have the rebuilt engine back in the car and we decided to tune it on a "rolling road" to make sure we got the mixture right.
So this is a 75 2.0 with standard FI and no emmissions gear on it. I had sort of hoped for around 75hp at the wheels but it has come out at 57hp rwhp.
Engine has new AA pistons and cylinders and the standard 2.0 heads so does this sort of number sound right and if it's way short what could be the problem.
Also, will it get better as the new pistons settle in.
I go get the car on Friday so will put some pics up then

[johannes]

Sounds very weak ...

[Mblizzard]

I thought brake horsepower (bhp) was the measure of an engine's horsepower (at e crank) before the loss in power caused by the gearbox, alternator, differential, and other components. So I have always been told that measuring HP at the wheels (dyno) will always result in a lower number than the published figures.

A 1975 has 88 HP as a published number. Without the emission stuff you are likely getting more than that. But 57 does seem a little low.

[VaccaRabite]

Well, starting at 88hp for a stock late 2.0, removing a third of that for drivetrain loss equals 58Hp.
If you had a 95Hp engine (stock non emission) you should have about 62 on the road.

You are a tad low, but reasonable.
Zach

[Bleyseng]

Bullshit! you have done something wrong like the CR is way off...Did you use flat top pistons or bus pistons with a huge dish?

This is my old test after I did my first Stock rebuild way back in 2000. There is very little loss with a 901 tranny certainly not 15%.
I did have the SS heat exchanger and a Bursch exhaust on it for this test.

[brant]

remember there is a HUGE dyno variance between brands/manufacturers...

some of the stock racing classes will only use a certified machine, and I believe at this time only 1 brand is certified ... although there are likely 20 brands made.

[hydroliftin]

I rebuilt my 2.0 a few years back and feel it gained significant power as it wore in. I discovered recently that the timing had been advanced way too much for several years. At last I found a mechanic smart enough to measure top dead center and not just rely on the timing mark. That was good for a huge inprovement in power and reduced head temps. Keep at it. Your motor can probably do better.

[porschefile2010]

Yes, not that I know a great deal about it, but I would have thought that as the pistons and rings settle in, friction would be reduced and power would lift somewhat. The engine had only 15 minutes on it when it was tune on the rollers. 57 did seem a bit weak though. I pick it up tomorrow and will see how it feels.

When I bought it it had a oversize 2.3 in it which I blew one head on so this second engine should feel less torquey and have more top end. Appreciate the input as usual and will report in Friday.

[SirAndy]

I thought brake horsepower (bhp) was the measure of an engine's horsepower (at e crank) before the loss in power caused by the gearbox, alternator, differential, and other components. So I have always been told that measuring HP at the wheels (dyno) will always result in a lower number than the published figures.

A 1975 has 88 HP as a published number. Without the emission stuff you are likely getting more than that. But 57 does seem a little low.

One thing to remember, in Europe at the time the 914 was build, HP was usually measured in DIN HP which is much closer to the rear wheel HP than the more commonly used SAE HP in the USA.

I'm pretty certain the factory rating of 88HP is pretty close to rear wheel HP ...
(IMG:style_emoticons/default/shades.gif)

[jd74914]

Yes, not that I know a great deal about it, but I would have thought that as the pistons and rings settle in, friction would be reduced and power would lift somewhat. The engine had only 15 minutes on it when it was tune on the rollers. 57 did seem a bit weak though. I pick it up tomorrow and will see how it feels.

I highly doubt the rings were sealing with only 15 minutes of run time...

[Dave_Darling]

One thing to remember, in Europe at the time the 914 was build, HP was usually measured in DIN HP which is much closer to the rear wheel HP than the more commonly used SAE HP in the USA.

I think you're referring to the SAE Gross power rating. That went out around 72 or 73, and the SAE Net rating was used instead. The Net standard was similar to, and possibly even a little more strict than, the DIN standard.

http://en.wikipedia.org/wiki/Horsepower#SAE_gross_power

If I recall correctly, the 914-6 made something like 120 SAE Gross HP, 110 DIN HP, and about 105 SAE Net HP.

All three standards call for measuring the power at the crankshaft, not at the drive wheels. There are drivetrain losses when measuring power at the wheels, but they can vary depending on a whole lot of factors. I have heard figures from 10% to 20% thrown around, but they could be more or could be less in any given case.

--DD

[porschefile2010]

I thought I had read that the early 2.0's put out around 95 at the crank and the later ones something like 80. I know there are differrent measure of bhp and I am not sure which one the books refer to but I suspect it would be SAE. So if it is 80 at the crank and I have 57 at the wheels we are in the ballpark with potential for it to improve as the engine runs in.
Not big numbers though are they ?

[johannes]

The dyno I made on my 1975 1.8 was following

Rear wheel HP 55,4
Transmission Loss HP 17,4
At the Crank HP 78,8

The car is stock but the catalysator that has been removed and a Bursch muffler.

Transmission loss is 22%

[bulitt]

So, we finally have the rebuilt engine back in the car and we decided to tune it on a "rolling road" to make sure we got the mixture right.
So this is a 75 2.0 with standard FI and no emmissions gear on it. I had sort of hoped for around 75hp at the wheels but it has come out at 57hp rwhp.
Engine has new AA pistons and cylinders and the standard 2.0 heads so does this sort of number sound right and if it's way short what could be the problem.
Also, will it get better as the new pistons settle in.
I go get the car on Friday so will put some pics up then

So they tuned the car on the dyno for you? Did they use a wideband O2 sensor to determine the A/F ratio? Did they use different plugs as they adjusted the ratio?
Did they tweak the timing? What is the condition of your clutch? New? Slipping? What injectors are you using?

[Bleyseng]

Look at picture of my stock 2.0L on a rolling dyno-91hp at the rear wheels. It was a total rebuild but with flat top pistons at 8 to 1 CR.
I had tuned the MPS and it looks totally correct if you look at the AFR 13.5 to 1.

55 RWHP is weak..... (IMG:style_emoticons/default/chair.gif)

[SirAndy]

Look at picture of my stock 2.0L on a rolling dyno-91hp at the rear wheels. It was a total rebuild but with flat top pistons at 8 to 1 CR.
I had tuned the MPS and it looks totally correct if you look at the AFR 13.5 to 1.

55 RWHP is weak..... (IMG:style_emoticons/default/chair.gif)

(IMG:style_emoticons/default/agree.gif)

[porschefile2010]

Just picking up on Geoff's point early on about pistons. I used the AA european flat tops. So they aren't dished and CR should be ok. I pick the car up this arvo so will speak to the guy who rebuilt the engine for me.

He said he had been very particular to check and recheck TDC and timing so I am hoping that's ok.
The other thing of course is how accurate thr machine is but 57 seems at least 10-15 hp off the mark.

they might have left the handbrake on!

[SirAndy]

57 seems at least 10-15 hp off the mark.

More like 30+ off the mark ...
(IMG:style_emoticons/default/popcorn[1].gif)

[Dave_Darling]

I thought I had read that the early 2.0's put out around 95 at the crank and the later ones something like 80. I know there are differrent measure of bhp and I am not sure which one the books refer to but I suspect it would be SAE.

73-74 2.0, US spec: 95 DIN HP
73-74 2.0, European spec: 100 DIN HP
75-76 2.0, US spec: 88 DIN HP

Note that all are DIN ratings.

I don't think I've seen specifically what the 75-76 European 2.0s made.

The difference between the US and European spec for the 73-74 2.0 cars was: 7.6:1 compression versus 8.0:1 compression. That's it.

The 75-76 US-spec cars had the 7.6:1 compression, and also had the nasty late-style exhaust, with or without catalyst.

--DD

[Bleyseng]

All Euro 914's had the 100 hp set up-8to1CR