PDA

View Full Version : Running rich up top?



OLDFLM
01-14-2008, 10:27 AM
71 Firebird 400 running WAY rich above 4000rpm... Holley 3310 750, quick change with silver (medium) spring, jettable secondaries, rear PV blocked, 4.5PV front, downlegs, 31 shooter... runs great on the street, just seems to lay down a little on the top end... I think there's more in it...

73s in the primaries... (CORRECTED)
85s out back is how I had it set it up initially… 80s is where is is now…
Which AF looks better to you?

RPM 80A/F 85A/F
2500 13.2 13.3
2750 12.7 13.0
3000 12.5 12.7
3250 12.7 12.7
3500 12.7 12.9
3750 12.2 13.3
4000 11.1 12.2
4250 10.7 12.0
4500 10.6 11.7
4750 10.5 11.5
5000 10.6 11.5
5250 11.0 11.4
5500 11.4 11.5
5750 11.7 11.6
5800 11.7 11.6

How much more hp do you think it has in it if I can get the A/F nailed down throughout the RPMs?
Peak power was at 5350rpm btw w/A/F at 11.2.

Thoughts/comments on where I should go with the carb tuning next...

V/R,
Ty

68Formula
01-14-2008, 11:03 AM
I don't understand why just changing the secondary jets from 85 to 80 made it richer until 5750rpm.

Anyway, with the same carb and a 455 I'm runnning 68s in front for economy and a 71 secondary plate out back. I didn't finish tuning it for WOT, but even with a 71 secondary plate (which I think is equivalent to a 71 jet) once it used up the pump shot, it was still less than 12.5:1 at WOT.

I'm assuming you hit it from down load in 2nd gear and stayed on it while using a data logging system? Make sure you are consistant. We had to record by hand doing street tuning, and I found out later my helper was not recording the WOT reading at the same point, so sometimes the pump shot was still added. (I'd hit it on the on-ramp at about 2500rpm in 2nd gear and then had to get out of it by 5000rpm)

OLDFLM
01-15-2008, 06:26 AM
The numbers above are from the 1st and 4th pulls from the car being on a SuperFlow chassis dyno last week...

Carb mods are as follows:
Baseplate:
Slabed throttleshafts
Throttleshafts teflon bushed
4- corner idle circuit added
Blueprinted WOT
# 330 Accel pump cam

Mainbody, M-blocks & Bowls
Choketower removed & blended
Venturi casting shelf removed & blended
Rear idle circuit (4-corner idle) added
New HP downleg boosters w/ shear step
New airbleeds
New bowl vents
# 31 Squiter
Elec choke modified for fast idle cam use only
Quick change vac sec housing & spring kit
Added active rear metering block
Modified F&R metering blocks to build specs
Rear PV blocked

Just wondering if it's as good as I can get it with a 3310 or if there's more left in it. From this point I really don't know what to try...

V/R,
Ty

Vegas69
01-15-2008, 08:10 AM
Does your air filter flow enough CFM? Next time pull it off and do a run.

68Formula
01-15-2008, 09:24 AM
I'd add a longer stud and do a run with 2 filters stacked rather than removing it. When I tuned with and without the air cleaner I found without it ran 10% richer without. I think it's because the airflow path is not as clean without the base in place.

Shaker455
01-16-2008, 07:11 PM
[Quote] Thoughts/comments on where I should go with the carb tuning next...

V/R,
Ty
__________________


Maybe you should ask the person who built it for you?

Tell me how your A/F got richer with leaner jets?...your reading something wrong.

What did the guy running the dyno have to say about that?

Is 78/85 w/4.5 PV how it was shipped to you??

I would think it should be more like 72 to 74 up front with 82 to 84 in back with no rear PV.

Once your jetting is in the correct range the hi speed airbleeds can be taylored to balance the A/F