I recently swapped out three 24# high impedance injectors (don't ask) for three 72# low impedance injectors. Obviously, I reset my hex switches for a much lower duty cycle to compensate for the substantially larger injectors. A data capture at low boost (limited to 6-psig) yielded good O2 voltages, 850mV. However, something bothers me. When the SF is working, my exhaust tone changes from a smooth tone to a somewhat "puttering" or a "wrap-wrap-wrap" kind of sound. It sounds like an old pickup with glasspacks! The puttering seems to coincide with the injector pulse rate. Is this normal? I never experienced this with the 24# injectors (at least not audible).

One other thing bothers me. At higher pulse rates, i.e. hex setting of 5 or higher, my fuel pressure drops. My friend says this is not a concern, as long as O2 voltage around 850 mV is sustained. This makes sense, but it just doesn't seem right. I run a Grand National in-tank pump and an ATI in-line (240 lph @ 60-psig). Sounds like one (or both) pumps are not adequate. Thoughts? Any insight would be appreciated.

 

Ditch your friend as a source of advice. You must not use the stock type O2 sensor to tune a blower car. Very bad mojo. You could see 850mV and still be way to lean. If the FP is dropping, you are out of pump and you must fix this before running under boost or doing any other tuning or trouble shooting. FP should rise with boost. Think of the stock FP regualtor as a 1:1 FMU.

I never observed the puttering sound, but fix the pumps and then see what you have.

Rich Krause

 

Ditch your friend as a source of advice. You must not use the stock type O2 sensor to tune a blower car. Very bad mojo. You could see 850mV and still be way to lean. If the FP is dropping, you are out of pump and you must fix this before running under boost or doing any other tuning or trouble shooting. FP should rise with boost. Think of the stock FP regualtor as a 1:1 FMU.

I never observed the puttering sound, but fix the pumps and then see what you have.

Rich Krause

 

My fuel pressure does rise with boost, close to a 1:1 ratio. It gets up to slightly over 60-psig, then depending on hex setting, either sustains or drops. Any suggestions on which pump(s) to use? Single or double? Thanks again.

Willie

 

Need to know more about your setup, especially boost and displacement, to be too specific about pumps. But a good single intak can support big hp. Unless you have a monster setup, a 255lph intank is most likely sufficient. Last years setup used a Bosch 255lph intank, stock lines and regulator, and a Kenne Belle Boost-a-Pump to support 733rwhp (M6).

Racetronix advertises on this site and seems to be knowledgable about LT1 fuel systems.

Rich Krause

 

Rich,

305 TPI
20-psig boost

Do you have a P/N for the Bosch pump? Is Kenne Belle's boost-a-pump similar to MSD's, which raises voltage with boost? Does Kenne Belle have a website? Also, why can't you tune a boosted application with the stock N/B?

Willie

 

Stock O2 sensor just tells you richer or leaner than 14.7, which is not enough information. At (for example) 850mV it might be 13.5:1 (too lean) or 12:1 (richer than needed).

If I were doing a single intank now I'd get the Walbro pump. I can find a pn if you like. Not familiar with the MSD product, but the KB BaP is boost sensitive and does increase voltage to the pump under boost. KB has a web site, but if decide to buy a BaP get it from www.kennedysdynotune.com for the after sales service, which isn't so great if you order directly from KB. KB is at http://www.kennebell.net/

Rich Krause

 

Appreciate the info (as always). I think I found the problem though. I've got the SF injectors and FP gauge plumbed into the test port on my fuel rail. I do not know about LT1/LS1 fuel rails, but mine has a restrictive passageway in the rail just below the Schrader valve (test port). A friend of mine had to drill his out somewhat to flow enough fuel for his nitrous setup. With this restriction, it's very possible my SF injectors & FP gauge are not seeing the fuel it requires. Time to get down and dirty and drill that orifice out. But because a fuel rail on a TPI is very labor intensive, I wonder if a better solution would be to tee into the 3/8" line somewhere in the engine compartment??? hmm....

Willie