head porting, and tune change

All,
I am running a blown alky BBC set up, the heads I run are the dart 360's with the dart CNC porting, and they flow about 365 CFM with my combo, I have been talking to Race Flow development and they claim the have a CNC program that can get these heads to flow a lot better some were close to 420 to 440 CFM
My question is if the heads flow more air to the cyclinders this will lean out the motor and if I run the same over drive I will need to fatten up the tune? or just drop a few teeth of over drive and keep the fuel the same? I just want to make sure i am correct? Any help would be greatly appreciated,

Thanks a ton

Butch

 

Head Flow

I will say about the RFD Dart 360's. I had them build me a set and the "claim" is accurate. Mine flow around 450CFM I haven't run them yet so I will leave the rest of the answer to the experts. You won't be disappointed.

Corey

 

Yes you are thinking correctly, more fuel or less blower. Personally for us less blower is not an option

Side note: If they still have the 2.300 valves in them I would be surprised if they will flow over 410 unless you lift them to .900". Let us know how they turn out or if you could please PM me the flowsheet.

 

If they flow more air they will make more power. That means it will require more fuel. From 370 to 420 cfm's would be around a 100 to 120 HP. Around a half a gallon at 8000 rpm's would be a safe fuel change. One thing to keep in mind when working with a cast head on a blown engine is the valves and guides move around a lot. The higher the boost and the bigger the cam and the higher the RPM's, the more they flex and move. Keep the guides long and the aluminum around them thick enough for some support. This will hurt the airflow, but your heads, seats and guides will have a much easier life.

 

Here's similiar example:
When the Dart Big M heads came out they "outflowed" the 360's "by a mile". Well, I don't recall the cfm numbers, but they didn't out do the 360's until after some higher lift, like .850 or so. I remember one friend took of his 360's and tried these and "couldn't tell the difference" but his cam only lifted the valve to .750", oooops

 

Here is something to think about in your spare time. If you install better flowing heads with a roots and mechanical injection you should not have to add any fuel. Your manifold pressure should drop and power go up.

 

Correct , more of the mixture gets into the cylinder instead of backing up in the manifold causing the manifold psi to go up .

 

Roots............. naw!!

OK Sufer Boy.... When ya gonna tell them it's a screw blower??

 

That is correct, depending on some other factors. Boost before and after, comp ratio, cam profile, ect... My short answer is still to add the extra fuel for the extra power and tune from there.

 

Comment from well known tuner "You can't go wrong with too much fuel, but you can't go fast either".

 

Tuning change when porting heads

All,
I just wanted to say thanks so much for all of the GREAT info, I will fatten up the AFR on my Davenport program and make the changes to the main jet for the first few passes and see what the plugs, computer and rod brings tell us.
This site is one of a kind, there is no were else you can find this many hi caliper racers/tuners willing to help!!!!! Thanks again !!!!!!!

Thank you Will for a Great web site!!!

Butch

 

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