Jets

[B1 ECC]

Hi everybody, I've just got the engine back in it's newly rebuilt state (Again). So I thought, before I blow this one, a survey would be a good idea.
If anyone is running a 750 double pumper with 400+ hp can you tell me your jet sizes.This would help as a "yardstick" comparison.
Thanks

[andycanam]

Ian
Good to hear from you again... glad you've got your engine sorted.

On the jet size, my dyno from AS (on their 500bhp package) says w/71/80 jets. not sure what that means but I do know that a dyno run on over here and my many hrs of track fun have proved it to be spot on...

To be 100% sure I'd have it run in on a dyno where the fueling would be monitored and adjusted if neccessary.

See you on the track.
Andy

[B1 ECC]

Andy,
Thanks for the info,good starting point.

Ian

[Steve_D]

My 407 engine goes back on the dyno Friday 9th.
It has an 800cfm carb which currently has 71/85 jets.
If all goes well then we should confirm or change those jets. I will post the results.
Steve

[B1 ECC]

Best of luck with the dyno run, the results should be really interesting!
Thanks for the info.

[davefiddes]

You might want to consider grabbing one of the wideband oxygen sensor boxes were were talking about on another thread. The boxes have the abilty to log the AFR and RPM (and other parameters if you wire up the sensors) and might be able to spot any issues which are causing your engine to run lean and toast itself.

I'm running a 700cfm carb on my 450 bhp engine so I don't think my jetting is particularly comparable. It's running 69/78 with 6.5 power valve.

[B1 ECC]

Dave,
Thanks for the input, i've had it rigged to a meter and that showed O.K. the AFR readings from the engine dyno runs are right on the money. I'm looking for a variable hence the gathering of info. The engine doesn't run lean, but it does detonate!

[davefiddes]

If the AFR is OK maybe the advance curve or plugs are wrong??

I was reading an interesting article yesterday evening about a guy with erratic timing causing funny fueling issues. He ended up converting from a halleffect distributor to a crank trigger. This cured the timing issues completely. Because the dist is at the end of a, comparatively, sloppy timing chain and dist gear the scatter make be pretty excessive...and/or only show up when the engine is under extreme load on track. You'd need some sort of ECU to replace the dist function but I think that such things can be had for reasonable money.

[andycanam]

B1 ECC said:

The engine doesn't run lean, but it does detonate!

I assume it didn't do this on the dyno though, only on track?

You still unable to track the problem down?

[B1 ECC]

Andy,
Yes, that's exactly it! It ran perfectly on the dyno, I even took the heads of afterwards and everything was perfect. 800 miles of road use to "run it in" no problems, 5 laps of Bruntingthorpe "Bang" asta la vista engine number five

Ian

[B1 ECC]

Thanks to everybody who contributed.