Have you had your 308 Dyno'd?

http://www.enjoythetrack.com/ferrari/Dyno.pdf

 

http://ferrarichat.com/forum/showthread.php?t=127791

 

Nick,
I very much hate to be the one to tell you, but your graph shows that your engine has problems. It should be making peak hp at 7500 rpm and that would give it about 30 more hp, but instead of pulling to redline, it starts to nose over at 6100 and crashes at 6300. Something's wrong.

Did you get and Air/Fuel graph when they did the run? That might help determine if its a mixture or ignition problem.

On a different note, it looks like a hub dyno not a rear wheel dyno is that right? did they give you any idea what the correction factor to crank might be? On a rear wheel dyno 17-18% seems to be the accepted number, but that includes tires losses which are probably about 5% I'd guess since running the tires at maximum inflation adds about 2-3% over running at normal pressure.

 

http://www.prahranair.com.au/308dyno.JPG

 

Autronic ECU? I love those. Used to be a great deal before the US dollar turned into a damn peso.

Aaron

 

Max advance on a carb 2v is somewhere around 40 degrees btdc I thought. A four valve car advance maxes at 34 degrees due to the more efficient combustion chamber, but the 2v needed more advance at higher rpm to completely burn the mixture. You may simply need to turn up the advance if that is so. I have a 2v advance graph at home I will try to post tonight.

 

On a hud dyno, I think the correct loss number is 10-12%.

The torque peak in the right spot says all is good to that point, but something is going wrong above 6000. It might be mixture. It's not an air restriction, that makes the hp flatline and you don't have that. It drop is suspicously like a what a cylinder missing would do, although that is usualy more abrupt, the dyno software adds "smoothing" to the results and could make it look tha way yours looks. I'd go after mixture first I think since you thing the igintion system is in good shape.

 

It's my understanding that the kind of dyno shown above gives very different readings than that of a rear wheel dyno because the rear wheels are not on. Peak bhp for these engines is much higher than 6k....

 

Those look a lot like QV advance points.
Do you know what carb jetting you have? I would not expect it to be lean as a Euro, but the truth is gas formulations have changed since the car was originally designed, and many find you have to enrichen the jetting to return to original output.
The other thing could be someone incorrectly timed the cams at the last belt change.
No worries, mate - Team FChat is here with mo shortage of opinions!!!!

 

Then I think 18% loss is inaccurate since carobu built a euro spec GT4 engine, made some improvements but kept within the "stock" guidelines and only arrived at 230HP, thats a fresh dyno tuned engine on an engine dyno. I doubt your original worn engine makes the same HP.

 

+1

 

I think Paul is talking about what loss factor to use. 18% is way too high for a hub dyno, but 10-12% makes sense...but that still gives a number that is a bit too high considering you are 20-30 hp low with whatever is wrong with the engine. Every brand dyno gives different results, that's just the way it is. For comparing, dynojets are pretty much the standard and I'm pretty sure you'd get a lower number on a dynojet and I think that is all Paul is saying, but what you're really looking for on the dyno is not a number, it's exactly what you found, a little problem that needs attention.

 

One thing many have not taken into consideration is that drivetrain loss for our cars is not 17-18% across the board. The power loss is linear across the power band. Power loss for our engines is speculated to be about 17-18% @ 6600-7000RPM. More energy to turn the transmission at higher rpm=more power loss due to gears. I believe we may lose a bit more than that due to the amount of gears the flywheel alone goes through prior to it even reaching the transmission. That means that at a lower rpm, the power loss is going to be less. A recent article called, "the horrible truth" in a hot rod magazine dyno tested a Ford v8 engine out of the car, and then in the car with full drivetrain attached (manual transmission). The car was some rear wheel drive '60s muscle car which I unfortunately cannot recall. It lost a staggering 27% (can't recall if it was 27% or 37%, either way it is a huge number) through the drivetrain at less than 5000rpm. It was the same engine. Read on:

Take a long piece of rope with a rock attached to the end of it. Swing it around so the rock is swinging around while the person is holding the opposite end without the rock. Swing the rope at 20 RPM. Note the amount of energy it takes to swing the rope at 20 RPM. Then swing the rope at 30 RPM, and note the energy difference. As the RPM increases, so is the energy required to increase rpm.

The case for your engine dictactes 190bhp at the hub (not at the wheels, which are a big factor) @ 6000rpm. Every healthy 308 I have seen has peak power @ 6500-7000 (stock engines). Being that peak power was made at 6000rpm with your car and the wheels were not on, I would hesitate to say it is entirely accurate.

 

Odd. I read an article with an olds something years ago dyno'd in and out and 15% loss, which is the excepted number for front engine rear drive. I thinkt he 17-18% number that gets thrown around for 308s comes from norwood dyno runs, but that might not be true.

I’m sure there is some merit to the loss % not being a constant %, it theory it should be, but there are many factors that could make reality different from theory.

 

At rear wheels Dynojet showed 211 peak hp @ 6600 rpm and 181 ft-lb tq. . . not sure of exact rpm peaks 'cause haven't had chance to look at raw data yet.

This engine has high compression pistons and aftermarket EFI system with stock cams and valve train. The guy started the pull at around 2600 rpm where it had about 170 ft-lb tq. Tq started falling away pretty fast after 6k rpm. Looking forward to see what the big cams do again.

Will post graphs and/or raw data if anyone wants.

Sean

 

See Aircon's Dynojet chassis dyno results for his GT4 in Australia. See page 4 of "Rejetting carbs" thread also unders 308/328/mondial. Go to page 4 Aircon's reply dated 9/25/07, open the link.

Aircon got 184 HP at about 6500RPM. 184 divided by 81% gives about 224 "engine HP"
But be sure to to look at his AF (air-fuel ratios) and his jetting. AF ratios seriously effect power output.

My '75 GT4 (with the earlier "more aggressive" cams) came with 220 AC (air correction jets). This is seriously lean where you actually want it a little fat (on top end).

I changed to 185 AC jets and the car became much stronger on the top end. Jetting now is 55 idle 135 main, 185 AC, F36 emulsion tubes. Very free flow Magaflow muffler. Works very well.

BTW dont go past 34 degrees BTDC on ignition advance (set at 6000 RPM).

 

more info on the EFI please?

 

post, post, post! QV or 2V?

Aaron

 

Of course we want you to post the graph man!

 

I got my GT4 dyno'd at a dynojet facility today: max rwhp: 190.61@6530 rpm max torque: 177.45@3750 rpm
I will try to scan the sheet soon and post a better picture.
Unfortunately the clutch died after the second run.

Rocco

Here are the car specs: 1975 US 308 GT4 stock motor with mille miglia muffler, itg foam air filter, crane ignition and 140/190/55 jets.
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