308GT4 Dyno results

Here you go
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Here's the corrected graph.
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No problem...I like to see dyno graphs.


Torque and HP are not independent. By definition HP=Torque*rpm/5252, therefore Torque=HP*5252/rpm

Russ is your guy for weber tuning. 12.5-13.2 is about where you want to be. An free flowing exhaust should lean it out a bit so do that before you spend time doing any other tuning.

 

It's been documented a few times that the forward motion of the car does not really give a pressure head to make much of a difference, but does keep a supply a cooler ambient air. As to runing without an airbox cover, there is a very big difference than running without in both hp (can be as much as 10), sound and mixture control - as you said, without having to suck as hard, the mixture will be a bit leaner typically with the airbox cover off.

Soapbox on: With the formulation of todays gas, I would not go leaner than a 125 main ever- or even use it - or even a 135 for that matter if your carbs are healthy (i.e. do not leak). If you really want to tweak it, a mobile A/F meter such as the Innovate LM-1 is great. I like to tune mine on the road - once you have the A?F where you want it, THEN go get the dyno as a mere formality or to set the best advance as it's the mixture that determines hp.

Nice dyno - have fun and good luck!

 

I've got 125's for mains and the car is still running fairly rich. At the same time, it's got loads and loads of power. I can keep up fairly well with 328's and have seen 7800 rpm in 5th gear with the car still accelerating (and without cheating: no wind and no hills).

Everybody is telling me that 125's should be too small for my engine, and yet they work excellent. In fact, the car choked on 135's and even on 130's.

I guess not all webers are created alike??? Or could it be that my idle jets are so obnoxiously large that these compensate for the smallish mains? Most of my flame throwing is with the throttle closed, coming down from high revs.... Haven't checked the idles yet...

When time permits, I'll stick the AF meter that I have laying around in the tailpipes and measure....

Hans

 

to me, light load looks too rich but i'd be really happy with the full throttle readings. one could argue that you need a larger air corrector, which is a bit odd to me...but that's beside the point. you might find the new exhaust will lean that out anyway.

regardless, i wouldn't be touching the mains.

 

Make sure that you do the well documented air box restriction mods while you are at it.
With all this work you are doing you want to make sure the car is breathing the best it can.
Sort of like having the right extractors/exhaust.

Steve.

 

aussie cars don't have the airbox restriction, do they?

i know mine doesn't.

 

hmmm

it'd probably be good to see just what you do have. You can check one of the outside ones to see what size. I'd sure agree you tune on what you see, however.
Just got the rpm kit and will try it out as I tune the new 44 carbs - will post the graphs in a few weeks.
I use an LM-1 with welded bung for the sensor.

The airbox silencing seemed to appear on late 70s cars here. Being as Oz is one of the last Lands of the Free, perhaps they got a break on this.

 

wow...that is SO wrong! i hope you misunderstood. 14.7:1 at WOT would possibly damage your engine.

12.5:1 is as close as you're going to get. a larger jet will make it 11.5:1 and a smaller one 13.5:1

14.7:1 is theoretical best lean burn for complete combustion and is meant to give best economy...not best power. my 50 idles give me btwn 14 and 14.5:1

50/135/F36/170

http://www.ferrarichat.com/forum/showthread.php?t=164562

 

no..my 135 mains gave 12.5:1 for most of the time, i think. AND....my limited experience demonstrated that it won't be completely even all the way anyway. 125s were lean as hell (down to 15:1) and 140s were 11.5:1

after setting up the motec on the 355, i was a bit disappointed with the results of the carbies...until i realised that that was as good as it gets and it was pretty damn good!

31mpg btwn canberra and melb was enough to put a smile on my face.

http://pless.com.au/cars/gt4/rebuild/images/308dyno.JPG

don't worry about the HP numbers...different dyno...different day.

 

31 mpg???

Holy smoke! The best I've ever seen was 16.5 mpg, and that was when I was driving on the Autobahn on the space saver tire. Normal fuel burn is 13.5 to 14 mpg....

Of course, I DO have a rather heavy throttle foot

 

PP's car is about the best tweaked carb car on the planet. Note that he uses 50 idles, and when we are cruising, we are mostly on the idle circuit. Rich idles cure a lot of ills quickly, but Aircon took the time to do it right and has the top end cover richness - you'll find a 170 a/c far richer than almost all other 308 applications. This allows the main to reach down and better cover transition, gives him power on top, yet allows the lean 50 idles to sip fuel at low throttle openings. I know I say this all the time, but we need to try to go with the leanest idles we can safely get away with and and compensate by bringing the main circuit in sooner. Rich idles tune faster to acceptable running and good power, but the economy is the price you pay.

Ferrari went at it in exactly the opposite way in the mid 70s by going to leaner mains -- now, fuel was formulated very differently back then so it is hard to directly compare. I don't know why they went that way - perhaps it was the best way to tune for the specific emissions test. Which leads me to another soapbox - if you are still running the same jetting from the 70s, well it is not the best as fuel is so very different now.

 

remember...imperial gallons!

 

Okay, but that would still get you nearly 26 miles per US gallon...

I will definately start tuning my carbs once

* I've got my new house finished
* I've got my new garage finished
* I've got that plane that is sitting in the workshop finished
* I've got that new propeller, gearbox, engine mount and cowling on my own plane finished...

Sigh... so much to do, so little time....

One question:

How do temp and altitude affect carb tuning?

In other words: If I'd tune for as-lean-as-possible at sea level in winter, would summer temps give richer, leaner or the same mixture? And altitude?

Thanks!

Hans

 

I see what you mean, I believe.

Question: whereabout does transition between idles and mains take place?

We tend to drive a fair bit faster here than you guys do in the US (or Oz for that matter). My cruising typically is at 140 to 150 kph (88-94 mph). I guess that's main jet territory?? What mixture would I aim for at those cruising speeds? Around 13.5?

Thanks

Hans