Dyno Results are In!!

[OZCarrera3]

Well, finally got the C3 dyno'd. I realise that these figures cannot be taken too seriously and mainly I wanted to do this just to see what the fuel ratio mixtures were like etc.

After rebuilding the motor with new late model SC (204hp '83) model pistons and barrels (i.e. up from 8.5:1 to 9.5:1 compression ratio - I think the later figure is correct), I had estimated that the engine would produce in the vecinity of about 220hp. The graphs indicate a maximum of 127.1kw (170hp) at the rear wheels, which translates to approximately 180kw (242hp) at the fly wheel using a 30% drive train loss factor (I know, this figure is arguably lees for 911's). In any case, I am fairly certain that I have achieved around 220hp which is adequately up on the 200hp the car came with from the factory.

My only concern is that the AFR seems a bit lean early in the rev range, is this normal or something that should be looked into further. Later in the rev range, the AFR is about right (assuming 12.5% is perfect)?

Here's the graphs for you to asses:

Graph with AFR and Power


Graph with Power and Torque

[OZCarrera3]

Oooppps!

Graphs are in the wrong order, power and torque are in the first shots - sorry guys.

[jorian]

"...translates to approximately 180kw (242hp) at the fly wheel using a 30% drive train loss factor."

Don't be so hard on yourself. It's more like 15%.

[Jack Olsen]

As has been said a number of times on this board, the only useful comparisons a dyno is really good for is A/B of the same car on the same dyno (preferably on the same day).

But even so, a 30% drivetrain loss figure? That's double the already-generous (commonly-used) figure of 15%. But the 15% figure would put you right at 200 crank hp. Did you dyno it before the mods?

Hopefully, an expert will sound in with some analysis of the A/F ratio.

[OZCarrera3]

Unfortunately I didn't get the car dyno'd before the rebuild, I agree this would have been the only way to truly know the improvement. I too thought the power loss figure was about 15%, but the guy at the dyno shop and a few others have assured me that its closer 30%. The dyno guy also said he had another C3 in there late last year and it only ran about 117kw at the rw.

Also, the increase in CR should net me some power gains shouldn't it?

At the end of the day I'm not too concerned (although the club may put me in a different category for the club championship now. We go on power to weight ratio), and would rather have the AFR figures verified.

Thanks for the feedback though.

[pjv911]

O.K. whats a C3 ?


Kurt Williams

[Bobboloo]

O.K. whats a C3 ?

Carrera 3.0

ROW 76/77' In the states the non turbo cars only came with 2.7Ls

The motor is built on the first(930) turbo cases that use the original version of the 70.4 crank.

[OZCarrera3]

Noah, thanks for the feedback on the AFR's.

The dyno shop tells me that there is not a lot more adjustment that can be done with the CIS, is this correct? As far as I'm aware, you can only adjust the mixture screw which does not give you the sort of fine tuning that we need here. I would be very interested to hear if you have other suggestions.

I'll check my records tonight, but I think the ROW SC's had higher compression ratio's to the US and yes, I'm running stock cams and exhaust.

[dd74]

Great work, Sheldon. Can you give us more details on the engine?

[asphaltgambler]

Try adjusting the main mixture screw first to see if it gets you a better AFR across the rpm range. Heat is energy, especially in an air-cooled engine. If your mixture is that fat you are killing HP /TQ.

[OZCarrera3]

dd74, the engine is basically standard except for the addition of the late ROW SC pistons and barrels (Noah, I checked my Oringinal Porsche 911 book and confirmed the CR is actually 9.8:1 for the 204hp Euro SCs, US models were 9.3:1) and some very basic 'cleaning up' or polishing of the inlet and exhaust ports.

Noah, would love (and plan) to fit some SSI's and a Monty exhaust in the future, but suspension work is my next project. Most of the suspension bushes and mounts are original and as you can imagine are what you might call 'tired'.

asphaltgambler, not sure what you mean by "If your mixture is that fat"? Do you mean its running too rich up high?

[dd74]

Sheldon - so conceivably, you built a Carrera 3.0 up with late Euro SC pistons, barrels and large bore CIS intakes and runners to come up with a motor that puts out over 240 hp. And it sounds as if you have stock cams in it and stock exhaust, right?

In a word - wow!

How's your low-end torque? Fairly strong?

[Jims5543]

Be careful of Dyno facilites AFR meters. I flew a tuner (Steve Kan) in from Texas to Florida to tune my RX-7 and after a few aborted pulls bue to rising AFR's we started changing the fuel maps.... to no avail.

We cross checked it against my Motec data log and they were not jiving.

Steve pulled his personal LM-1 out of his duffle bag and hooked it up to my car, we did another pull. The LM-1 agreed with my Motec, two against one wins. The shops dyno AFR device was wrong. Fortunatly it was showing leaner that actual so in a way it was safe but it was also very frustrating.

Cross check your AFR's next time you might be suprised.

[Wil Ferch]

30% drive train loss factor ??....LOL !

If anything, the transaxle design efficiency would often use a slightly "less" than the common convention of 15%...maybe even down to 8-10% loss.

30% makes for bar-room bragging rights HP.....

Wil

[pjv911]

Originally posted by Bobboloo
Carrera 3.0

ROW 76/77' In the states the non turbo cars only came with 2.7Ls

The motor is built on the first(930) turbo cases that use the original version of the 70.4 crank.

Thanks

[Jack Olsen]

Originally posted by Wil Ferch
30% makes for bar-room bragging rights...

Except for the poor guy who designed the transaxle.

[OZCarrera3]

As I said in my intial post, I was not about to take these figures seriously. I think it is reasonable to assume a figure in the vecinity of UP TO 220hp (only a 10% increase) given that standard car generates at least 200hp with considerably lower compression.

...maybe even down to 8-10% loss

Wil are you serious? I know Porsche are a remarkable engineering company, but I have not heard of drive train losses lower than about 15%. 8% would have my car producing only 185hp and my car has significantly more grunt than a standard 180hp SC (and I have done a back to back comparison).

Anyway, it all makes for an interesting discussion huh?

[SteveF_911]

Sheldon, I have used the same dyno shop as have about 20 other porsche owners I know.

In 4th gear as close to 1:1 gear ratio as possible the drive train and tyre power loss was worked out at about 34%. Which is what our club basses power figures for our club championship.

Whatever the true power is our motorsport committee will look at the figures and class you accordingly. I suspect they will put you at around the 220hp.

Oh well I guess it is time to work on the suspension.

[beepbeep]

Dude, you built yourself plain vanilla ROW 3.0 CIS car....one of those 204hp ones. Believeing you have 240hp+ on CIS and stock cams is wishfull thinking. Nothing wrong with 200hp either.

Drivetrain loss figures of 34% are laughable and most certainly not correct. It makes you believe you have a powerful engine though. Figures for Porsche 915 transaxle vary from 9% to 15%. 34% losses @ 240hp would imply a heat loss of 60kW inside transmission...imagine heating up your tranny with 60kW heater, that thing would glow after any longer full-power run.

In the end, only thing that matters is what reaches the road...you might as well say that you have 1000hp engine and 83% drivetrain loss if it makes you feel better...you are pedalling forward with 170hp and that's what there is.

[Bill Verburg]

Dude, you built yourself plain vanilla ROW 3.0 CIS car....one of those 204hp ones. Believeing you have 240hp+ on CIS and stock cams is wishfull thinking. Nothing wrong with 200hp either

I've Gotta agree