Hi all,

I've searched everywhere, but can't seem to find an exact answer to my question. My car (1988 Trans Am GTA) is getting a new motor - it's going to be a 383 with a Super Ram, ported Edelbrock base and a 58mm BBK throttle body. This is going into a street car, so no wild cam or nitrous. No S/C yet, although I'm not ruling it out for the future.

I'm shooting for somewhere between 400-500 HP at the wheels. Once it's all put together, I'm going to either try tackling the chip burning myself (scary) , or have one burnt to my engine specs. Possibly going to convert to SD along the way, as I understand it's easier to tune with a larger motor than my current MAF system.

My question is - what injectors would be a good fit? I'm pretty sure 30s will be too small, but 42s seem kind of large for this setup.

I was thinking 36#s would be a good fit, but those don't seem very commonly used - they're kind of hard to find (especially used), and Summit only lists Accels in 36#. Based on what I've read here, (and other places) I'm avoiding those. I would like to use FMS injectors, as I've heard good things about them, but the only ones that seem to be available in the range I'm looking at are 30# and 42# sizes.

Question - is there any reason NOT to use the FMS 42# injectors, if the chip is burnt with those in mind? Can I run those at a lower duty cycle to simulate smaller injectors - in other words, "throttle them back?"
Or will they have atomization problems, or just dump too much fuel, or not run properly, etc? I was thinking it would also be nice to have the option to "grow into them" if I add a supercharger or something later.

I'm new at this, and don't want to get the wrong parts...

I'm new to this too, but I've read alot of opinions in this forum. From what I understand, one reason NOT to use them would be that it's a waste of money. Check this site out and try the injector calculator, it helped me to my decision to stick with 30lb injectors

http://www.injector.com/injectorsele...891aabc14d0044

Good Luck....
Eric

Thanks Eric,

I checked that calculator - it said that the recommended lb/hr injector rating for a 450HP motor is 35.16. I think 30#s would be just too small - they'd be overworked, and running at close to 100% DC at WOT. I would worry about going lean, unless I ran the FP higher than the 43.5 PSI they're rated at. But then, I'd be putting a lot of strain on my FP.

I can find 42# injectors all day long used - I'm in no hurry, so I can wait around for a good deal to pop up. I've already seen a couple sets of used FMS 42 lb'ers go for $100-140 in classifieds, so it's not really the money issue.

Cool. I installed a 67gph fuel pump in my car to handle the upcoming mods. I'm gonna run the fuel pressure up to around 48 or so pounds. I don't THINK bumping the pressure will hurt your pump (assuming it's stock) If money's no object then 42s sound ok for your application. The new PROM would be MANDATORY should you go that route. Be sure if you buy them used, that you get them cleaned and flow matched.

BTW, anybody know if I should have my NEW injectors flow matched before I install them? If so, is there anywhere anyone would recommend to do the work?

Eric

That was one of the things I was going to do in the future - replace my stock pump with a higher flowing unit. But I kind of need to do the engine now, since I think the one in there has a cracked head or block.

It's not that money is no object - but I can get a set of 42#s much more easily and cheaper than a set of 36#s. I don't want to go any lower than 36#s for this setup.

Depending on the age / condition of whatever injectors I end up with, I was going to send them to Cruzin Performance for cleaning / flow matching. A lot of people have used them, and have had good results. I don't know if it would be worth the $120+shipping to have that done with new injectors though, unless you were building a high-dollar all out race car.

EDIT: Huh, weird. The site seems to be down. I was just on it yesterday!

What value did you use for the BSFC? EFI engines are more efficient than .5, Plug in .45, or even .42, and see what you come up with. IMO, #42s are plenty large. If you are planning on tuning your own EPROMS, you might consider the #30s. BTW, I have #36s on my 436, and #30s just might find their way in there yet.

I was using 0.5 for BSFC - I'm not sure what the actual constant is for these engines, so I wanted to err on the side of requiring too much fuel, rather than too little. Entering 0.45 BSFC, with 80% DC yields consumption of 31.64 lb/hr for a 450 hp engine, which is a good estimate of what I plan on running.

I'm still thinking the 30# will be a bit low - I don't want to overwork my injectors and have them fail on me. I know the 42#s are too big for this application (at least, running at 80% DC) however if you enter specs for a 450 HP engine, with 0.45 BSFC, and the injectors running at 60% DC, that puts the required injector size right around 42#.

Is there any difference between running a large injector at 60% DC, vs a smaller injector at 80%?

brutalform, what kind of HP numbers are you putting out? And what kind of intake are you running? Are you having any problems with the 36# on your car now?

36#/hr FMS injectors are rated at 39.5 psi. At the 36#/hr flow, you can make about 460 Hp. But with the fuel pressure turned up to 52 psi, you can make over 530 Hp. And these numbers are with a duty cycle of 80% at WOT.

Personally, I think the 42s may have a problem with idle. I have read somewhere where the PW for an injector should not be less than 0.7msec. The 42s seem very large. I'm getting away with 24#/hr FMS injectors on my 395.

So, you should consider WOT needs as well as idle issues.

Also, you should install a large fuel pump to supply large injectors.

About 2 1/2 years ago, after the engine was built, it made 490 hp, and 569 lb,ft on the engine dyno. It was dynoed with the EFI SuperRam intact, and we had used a mail order ASM EPROM. The engine was REAL ,REAL rich, that it would not rev beyond 5000 RPM. Thats where the 490 was cut off. At least it managed the TQ at 3500 RPM. After getting into doing my own EPROMS, It was a real eye opener to see just what was NOT done to my EPROM. No problems with the #36s, but I have more fuel than I need. I believe #30s would have been a better choice. My friend, Floorguy, is using #24s in his S/R 383, and he is running 11.80s in a full trim vette.

Do you know where I could get 36 lb FMS injectors? All I see being sold seems to be 30s and 42s...

I don't think I'm going to consider getting 42#s anymore, based on what I've read. It seems that many people are running 30-36 lbs with large-displacement SBCs and not having any problems. Besides, I don't want to worry about my idle, or using too much fuel, straining my pump, etc.

I think I'm probably gonna have to live with my stock pump for at least a little while, once the motor goes in - does anyone know what the limits of the stock pump are, in terms of fuel delivery, pressure, etc...I'm trying to figure out what pressure and injector size the stock pump will reliably support.

Hm, interesting, as that is the same intake setup I'll be running. What are the details of your setup, if you don't mind me asking? Is it a track only car, or a street / strip car? Streetable cam, pump gas, etc?

Does your friend with the Vette have his pressure up real high to be able to support that engine w/24#s? Hm, I may consider just getting some 30#s and being done with it - it seems like many people are getting away with less than that, with good results.

I'll look for an exact number later, but I THINK the stock pump max's out at around 30gph and usually they are run between 36-42 psi (probably closer to early 40s). I have the numbers at home (at work now) so I'll look them up later. For what it's worth, if you put the new injectors in and leave the stock pump, I doubt you'll get much more power from them as they will be limited by the stock pump.

Eric

No believe it or not, he runs lower pressure than 3 bar. I think its around 39 psi.

My car is street/strip. The cam is a "small" solid roller, 236/242 @ .050. Runs on pump gas.

Another source for injectors:

http://www.racetronix.com/621020.html

30GPH....man, looks like I'll be doing that at the same time. I think I'd cry if I leaned out my new $$$ motor and blew it up because of a crap fuel pump.

This is one expensive hobby! My bank account is gonna hate me, but if it's gotta be done, it's gotta be done.

That's awesome news. That's almost exactly what I'm going to be doing - roller setup, street cam, 93 octane pump gas. That's amazing that he gets those kind of times out of 24#s at around stock pressure! He doesn't worry about going lean?

Wow, looks like I may have found a source for my injectors. $240 a set for 32#s is a great price for new injectors. I might even get my fuel pump from them too, as it looks like I'll have to do that as well.

Do you (or anyone) have any experience with these injectors? How would they compare to say a FMS set?

I've got their pump setup and these injectors. I just put them on a month ago and so far they have worked great.

If you go to Racetronix, be sure to look for injectors that are flow rated at our fuel pressure, which is 43.5psi. Do not buy an LS1 type injector, the flow rating is off and its about 0.12" shorter in length.

I have bought from Racetronix in the past, they seem to be pretty good. Also, they do run sales every once in a while.

You can get 36#/hr FMS injectors from Summit Racing and directly from Ford Motorsports. I do not have Ford's website to quote you, do a search.

BTW: At work I check Fords site once in a while (I work at Ford now), I have not seen 30#/hr injectors offered on Ford's site.

But, I'm running the 24#/hr FMS injectors in my 395, and I am getting close to the limit on these injectors. If no power adder is used, the 30#/hr injectors with a better fuel pump (I installed the TTA fuel pump), and an AFPR should be plenty of fuel.

Well, I just did it. I ordered their GSS340M fuel pump kit with harness, and a set of 32 lb/hr injectors. Dinged my wallet pretty good, but it should be a nice setup. All on sale, as well (according to the site, anyway.)

I double checked the injectors, and they are rated at 43.5 psi, so that's OK - and the fuel pump should be more than adequate. They had a lower capacity pump that would have been fine, but that kit was only $10 less than the one with the higher rating, so I just got the better one.

I already have a Holley and a BBK (I think) AFPR - I had the Holley on my old TPI setup before, and the BBK came on the used Super Ram I bought. I'm probably gonna stick with the Holley, as I like the easy fuel pressure adjustment with the large wheel.

Thanks to everyone who helped, you guys have been great!

That sounds great! Good luck.

I agree with you, the Holley AFPR makes it easy to adjust the fuel pressure. I have a fuel pressure gauge hooked up full time in the engine bay, so I dont even need to hook it up and disconnect it.

Hey Black, is that an intank, or in line mount pump?

It's an in-tank pump. It's supposed to just drop right in place of the stocker.

My fuel pressure is quite low. I normally run 37psi. The car likes that pressure. I have a set of 22's laying around. I may put those in instead.