Dyno graph

[Mr Beau]

98 RON equates to about 93 pump in North America. With the CR at 11.3:1, this is a bit aggressive, but the largish cams help to reduce this. With total advance under 30 degrees, your probably safe, but at the same time, leaving power on the table without more octane or twin plug.

Judging by the general appearance of the graph, I would guess the mixture is way off. I'll guess lean (as in lean of stoich), but it could also be pig rich.

What do the plugs look like?

You really need to get a wideband O2 on there and confirm the ignition timing.

[obrut]

Matt

We will all say a little prayer to the gods of air/fuel ratio to get you through the next few days. From what I have heard of John G's work - the base engine will be perfect so that means its simply a tuning issue.

My (now departed) 70 911E would not run to redline at all when i first got it - one MFI tune up later and it was transformed.

Cheers - Ryan

ps: this probably goes without saying but i would minimize driving it until you know whats going on as either too lean or too rich can cause damage.

[Langers]

Matt, if I remember correctly you had the injectors tested and told they were "marginal" but not in what sense they were marginal? Is that correct?
Did John Gregory tell you anything about the engine other than it was on the very upper limit of single plugs? Perhaps there is a secret to be discovered there.

[Tyson Schmidt]

That really is too high for single plug on 93 (our equivelent) octane. But what I was worried about in my original post was that you may have been running more advance than necessary with twin-plug.

But since that isn't the case, then it becomes an issue of simply setting the timing where it won't detonate, and getting the fuel mixture set as close to 13/1 under load, and pay particular attention to what the mixture is at the top-end. You don't want to melt a piston from a high rpm lean condition.

[Early_S_Man]

I guess beep ... coming from the real world of turbo lag ... is blind to the lag in autofocus camera's shutters, EFI, and other state-of-the-art dsp application that are not quite instantaneous! The real-world response is a delay in EFI response is in the HUNDREDS of milliseconds, not MICROSECONDS!!!

That is only a difference of three orders of magnitude!

ps ... I assume the 'N' on the right axis means Newton-meters ... there does seem to be a missing decimal place, though.

[Matt Holcomb]

Matt,

Well, when I last saw the plugs, I had a weird (gut) reaction to them. I didn't say anything because I assumed they had to be okay if my mechanic was putting them back in the engine.

It'll be interesting to see what they look like next week …


Ryan,

What's your opinion of the compression ratio in relation to the ignition system? Would you have questioned John? Or would you have also deferred to his experience?


Klaus,

I'll be having the injectors tested next week. I guess we'll soon know what Gus meant when he said "marginal".


Tyson,

If the car is developing the power it should be after next week's tune up, should I still be concerned about the compression ratio? What you would you if you were in my shoes? I currently lack the funds to have it twin-plugged or to take a compression point off the pistons. But if I did have the funds, I'd probably seek legal advice before shelling out the dough.


Matt Holcomb
MFIWDP
1974 911 Carrera 2.7 (RoW)
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[SteveF_911]

162 kph What gear were you using? 3rd or 4th?

It is a bit hard to tell to much until you get the AFR.

I have had my car on three different Dyno within weeks of each other and the HP varied by about 60hp at the rear wheel. From 101 to 160, the real figure at the flywheel is 152, I guess it has a lot to do with the set-up of the dyno.

Does the car pull well when you compare it to a SC or a 3.2? Or is it off song?

[obrut]

Matt

most of the stuff i've read indicates that about 10.5:1 is the top comp ratio for single plug/high quality pump gas. but, to some extent, pinging can be controlled by ignition advance (but at the expense of some power).

did the dyno guy say it was detonating/pinging? - its pretty noticeable and they should be on the look out for it

high lift cams reduce the effective comp ratio somewhat too (i understand that, in terms of increasing lift, you have S, GE60, GE80, RSR) - so that is also on your side

if jg thought your thing would run well as is on good pump gas then, given his rep, i would be inclined to agree

i would get the thing re-tuned, check everything including the a/f ratio, then re dyno before you think of getting back into the engine

maybe consider having a fresh set of eyes look at it??

Ryan

ps: is there any chance you could have a tank full of crap gas?? the no name service stations in nsw sell some horrible mixtures...

pps: the 911E i mentioned above was 'tuned' by 2 well known nsw shops are never ran well - the 3rd guy took the time to get it right (purely settings no new parts) and has had all my work ever since

[obrut]

ps: just called my guy - no real diagnosis possible without the a/f curve

[Victor]

Krikey mate, stone the crows.

Was it running like that at Calder Park Sprints?????

[Matt Holcomb]

Ryan,

Have you shown your mechanic the dyno graph?


Victor,

Look, it probably was -- I haven't done many k's since the Calder Sprints, and it feels the same to drive as it did then.

Given the car's (theoretical) power-to-weight ratio, I thought that a 1m 13s at Calder was a little on the slow side.

Paul Stuart can lap Calder in 1m 08s in his Carrera 2.7 -- at 8 or 9/10ths.


Matt Holcomb
MFIWDP
1974 911 Carrera 2.7 (RoW)
Dedicated Homepage
Engine Rebuild Homepage
Pelican Gallery Profile

[stuartj]

Matt
94kw at the wheels, using 1.31 which PCV uses, translates to 123kw at the flywheel.

I have a chart showing my 3.2 doing 107kw at the wheels, which is 140 at the wheels, handbook says 152kw.

So what are you looking for? Lucky its light.....

stuart

[obrut]

Nope - was on the phone to him on another matter (the high comp 7R MFI engine that I'm building actually...) and described it. a/f ratio first thing to check.

[Matt Holcomb]

Stuart,

I was expecting around 160-170kW at the flywheel. With measly 8.5:1 pistons, these engines are good for 155kW at the flywheel.


Matt Holcomb
MFIWDP
1974 911 Carrera 2.7 (RoW)
Dedicated Homepage
Engine Rebuild Homepage
Pelican Gallery Profile