First of all wanted to say hello to everyone. Found your site referenced quite a bit at chevelletech.com. I've been kicking around a TPI setup on my chevelle for quite a while and finally found a setup which I think might work well for my engine. I've recently purchased a FIRST INJECTIONS system. I am into deciding on a injector size. My 383 has the GM "hot cam" along with edelbrock RPM heads and 9.5-1 compression or so. I'm looking for opinions on choosing the injectors. I thought that 30lb injectors would be about right but First Injections suggested 24lbs thogh they assured me they would swap out for 30's if I wasn't happy with the 24's. Anyone have any real world experience with FI systems or a similar combo. Any input would be appreciated.
Thanks in advance.
Jack

 

If your 383 is going to make 400+ hp or there abouts..go with 30's. 24's may "work" but may go static when you mash the loud pedal.

 

Yep, I agree with Morley, go with the 30s, you should be around 43 to 45 psi for the fuel pressure. Just be sure to install an AFPR (adjustable fuel pressure regulator). The AFPR will give you a bit of tunability.

Also, You will need a fuel pump to match those 30#/hr injectors.

 

I am making 510 hp and my 32# injector start running at 96% @ 46 lbs around 5600 rpm. I may go up to 36# if I find it to be a problem.

 

Thanks for the replys...I spoke with FI yesterday eve and here's part of his reply...

IF YOU DID FIND THE 24# INJECTORS WERE TO SMALL, I WOULD JUST HAVE YOU SEND THEM BACK WITH THE PROM AND SEND THE 30# INJECTORS AND THE NEW PROM TO YOU AT NO CHARGE. THE MOST COMMON PROBLEM THAT I HAVE RUN ACROSS SELLING FUEL INJECTIONS IS OVER INJECTING. I HAVE PLENTY OF 30# INJECTORS IN STOCK BECAUSE EVERYONE THAT ORDERS THEM ENDS UP SENDING THEM BACK FOR THE 24# INJECTORS. NORMALLY THE 30'S END UP IN THE BIG BLOCK APPLICATIONS. I CHECKED THE FORMULA FOR YOU AND A 400 HORSE ENGINE WOULD TECHNICALLY USE A 25# INJECTOR. YOU CAN CHECK WITH THIS FORMULA BHP X BSFC (WHICH IS TYPICALLY .50) DIVIDE THAT NUMBER BY THE NUMBER OF CYLINDERS ( WHICH WOULD BE 8) AND YOU SHOULD GET 25. YOU WOULD NEED IN EXCESS OF 475 HORSE TO REQUIRE A 30# INJECTOR.

I got a similar response from TPIS.

Now I think that my engine probably makes in excess of 400hp but I've never dyno it so I can't say for sure. I figure I'll just go with his suggestion since its his system. He might not be so willing to exchange if I insisted on 30's and found out they were
too big... I should be able to monitor duty cycle with Tech1.
Thanks again for your input. I'l probably be bugging you guys more along the way..I've always liked the tpi look. If it doesn't work out I'll can always transplant to the wife's 91 firebird...

I might add that First Injection seems like great people to deal with....

 

FWIW: I am using 24#/hr Ford Racing injectors in my 395 cu.in. stroker. I have the AFPR set at 52 psi, so the 24s are actually flowing about 27#/hr. But I pulled only 340 RWHP with my current setup.

The main problem with too much injector is the PW during idle is very short and can lead to idle stability problems. You should never run an injector under 0.8 msec. A minimum PW of 1.0 should be adhered to. With my current setup, the PW at idle is 1.3 msec (with the 24s at 52psi).

So, I guess that you should take their advice and go with the 24s. Afterall, they will swap with you for 30s in you need them.
So you cant go wrong with their deal.

But dont forget about the AFPR.