Hat only, but #3 way lean? BBC

Hey, both times (2 so far) #3 has been much leaner than others, next one is #6, but thats way more "normal".

I understand that without ports the holes are different, but thats quite a lot!

Stripped 8-71 std helix, conventional port BBC, 7/4 2/3 swap cam (18726543). Overdrive 25% and 38.6%, boost 15-19. 11.5:1

Thank You!
Partel

 

hat only tunes

thats the problem with hat only. you tune to the leanest hole. that said, is this a delta opening or large rectangular opening in the hat and in the manifold? different manifolds can have an effect on fuel distribution also. depending on how fast you want to go (7.0?) you will have to play with the nozzle sizes in different areas. and watch the fuel pressures, etc. give alittle more detail about the combination and others smarter than me will surely help out.

 

540 Big M
8-71 TBS std, stripped
Large top&bottom
Edelbrock #7765 heads

E110 pump (13.2 gpm)
Jets recommended for 25% OD were 58/56/56/54 + 125.

After going 38.6% OD: 60/58/58/56 + 115

32* timing

I know cylinders are different, but #3 is way off.

 

Two things come to mind.
1-Look at the port divider inbetween #1 and #3 in the intake. Is it sharp, funny things happen if the divider is sharp. Take your die grinder and shape it into a big radiussed end.

2-Are your nozzles flowed? you may not have as big of a nozzle their as you think.

 

Put The Port Nozzles And Be Finished With It

 

If you can't do anything else, Put a colder plug in that hole.

 

one thing after running a blown big block chevy for years my advice would be put the down nozzles in it like shawn said it will be easier to tune you can manage the power of the motor better and tune each cylinder accordingly with just hat nozzles and 38* timing and 47 over with a 1071 standard kuhl blower it was like a bomb went off when i hit the throttle with a power glide trans i didnt have any trouble spinning the tires and i never knew which way it was going to go but it put on a good show ( lol ) i believe the downs nozzles would help

 

That is odd (I guess). Many years ago I ran the same basic combo (~11-1 compression) with a smaller BBCs (441-503). With a Cragar intake, 2 and 4 were traditionally the hot ones. I agree with eli on the short term, try a colder plug. However, I look back and wish I would have tried port nozzles.

 

Many years ago I had about the same combo as you,just running hat nozzles in a big block chev. Try this- left side-front to back-60 70 60 57 right side front to back 60 59 65 59. sounds crazy but it gave me an even burn! A old tuner gave me this nozzle stagger,when I was having the same problems as you. You might need to lean the the main jet a little being that these nozzles are bigger.

-Dale

 

It worked! Thanks!
Front
64 / 62
67 / 64
62 / 64
58 / 58
Back
Not perfect by any means, but much better! Will go with ports anyway...
I have one idea why #3 was lean: the cam is double swap i.e. 18726543. Didn't click right away, that this means 18726543-18726543, adjacent #3 and #1 are in sequence, like the 5/7 issue with stock F/O cams.
Mixture stealing?

 

possibly. No matter how you swap a chevy, two are always fighting somewhere, you just move that pair around.

I'm going to ports on my small chevy just to tune with. majority of thefuel will be up top still.