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911st 911st is offline
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Join Date: Jan 2004
Location: Sacramento
Posts: 7,269
HF Fuel Distributor/ Head. How much CIS HP? CIS FlowTech

How much fuel or HP we can support with CIS will always be a question. Yes, EFI may be a better solution but some of us just love CIS and would not think of changing.

330HP stock
400hp with fat CO adjustment.
450 w lowered control pressure
500HP with HF, non lambda FD.
600hp with HF, Lambda FD set for extreme flow
700hp w max HF plus 8 bar system pressure
900hp+ w custom HF 8 cylinder Bentley head.


Larry at CISFLOWTECH ( 251-929-3771 ) is still modifying 930 Fuel Distributors (FD) to flow more fuel if anyone is interested.

For what it is worth, there is nothing magical about what he dose but he has perfected it and dose it well. It is always a good idea to think of having even the stock head rebuilt at this point to ensure accurate fueling and having the head set for more flow dose not add much to the cost.

He did the first HF head based on my ideas and request some 7 years ago for Brent930. We are lucky IA adopted it and popularized it as a very successful product.

Larry mentioned that a significant number of HF owner’s have had drivability issues as they did not know how to set up the WUR to control the head.

Anyone thinking of going this direction needs to know that manipulating WUR control pressures is key to drivability and successfully getting more fuel from this approach.

For example, if one can get 14.5/1 AFR at idle and cruse with a stock system, a HF FD that flows say 15% more fuel, once idle CO is readjusted to say 14.5 AFR, is probably going to be at about 12.3 AFR on cruse which is to rich unless it is a race car.

To get a proper cruse AFR with a HF-FD, base control pressure (CP) will have to be increased. This will slow the rate the sensor plate advances and bring the cruse AFR back toward a proper setting. Think of it this way, if the FD flows 10% more flow, we need to slow the metering progression 10% to keep stock AFR’s on part throttle.

However, most do not think of it but doing this will bring a bit of a negative effect on lag as it will present more resistance at the air sensor/metering plate and will create more fight with the turbo's effort to try to suck in air.

Thus, it is probably a better approach to exhaust all efforts to get more fuel from the stock FD before adding fuel by modifying the FD.

Last edited by 911st; 01-26-2010 at 01:06 PM..
Old 01-26-2010, 01:01 PM
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