AFR Big Chief Heads

Howdy...

Has anyone got some experience with Big Chief heads and calculated best AFR for good power without burning parts... My combo is a New Century / Arias 526 with Big Chiefs and a 14/71 Superman. I have been bitten in the backside twice now with AFR's that should work fine with a conventional wedge BBC. These heads with this blower obviously need way more fuel...

Cheers Pete

 

afr

I don't use afr calculations but I know how many GPM it takes to go fast with a big chief roots or screw. Do you have a flowmeter?

 

No I don't have a flow meter, the fuel system ghas been flowed so I guess i could calculate what it is flowing whithin a fair margin. I race in a bracket class so going as fast as possible is not quite as important to me as having a repeatable and safe tune...

Would love to know a flow number for referance, I have fitting for a flow meter so I might be able to get hold of one for a meeting or two...


Cheers Pete

 

chevy

The good thing about a big chief is it will go fast even fat and safe. We ran a 540 with stock heads and a k9 superman with mods at 37%OD. In 600 ft air I had the main pill plugged with a 990 enderle pump. It was running 4 teens at 2900lbs so making good steam.I think around 42 lbs of boost at 8800rpm.

Our screw setup runs way richer than any hemi. It will go pretty quick with full cad on the plugs and no oil dilution.
The only way I know to hurt one is with timing and crazy rpm above 9k.

 

I am running 20% over, I am not 100% sure what series Superman it is as I got it second hand and cant find any markings that mean anything. I run a 990 pump and the system was set up with a .090 sizer so looking at around 9 gpm at 8000 rpm with .130 main pill.
Our track see's DA's from 2-300 feet right through through to 3500ft plus as we are only a couple of miles from the sea. I am running a Mallory mag at this stage, looking towards am MSD when I can get the bucks together.

So from this and your experience it looks like I need quite a bit more fuel???

Thanks for your interest
Pete

 

chevy

I never ran a pump sizer or a main that lean. At least block off the pump sizer and make a 330 hit and check plugs. You have a 2000hp bullet easily. I can't imagine 9 gpm keeping pistons happy in decent air.
I think my 990 made 15 gpm at 8000 and i put every drop into the engine and the plugs were burned to the second thread.

 

Pump was flowed at 15.51 GPM @ 8000... Do you recall what egt's you would see typically at 330

Pete

 

Hey Overkill...
How much timing are you using?

Cheers Pete

 

timing

32 max with 43psi from kobelco.

 

Thanks

I am still way under that 27* @ 32 lbs line on plus barely making the turn on the plugs so it is a fuel issue only that I am dealing with

Pete

 

Are you changing the Main jet as the air changes?

 

The car has not had this blown engine in it for very long. I am following the weather but it looks like the baseline I started out with was out of the ball park to start with. The plugs and temps to 330 and then to half track looked fine, my mistake I guess was not then running to 3/4 track before a full track pass. When I get back to the track I will put a bunch more fuel in it. Reason I started the thread was to try and fast track the process a bit a find out what other guys have been running successfully and safely as the AFR these heads and blower want compared to a convential BBC 23* head is bucket loads more...

Pete