Fueling & Injection - Upgraded Injectors on a 347cid H & C car....

What is the benefit of going to bigger injectors on a basically stock displacement H & C car? I know they are recommended on high HP H & C applications but what are the reasons? Lower duty cycle? More power? Better atomization?
Phillip

mine wouldn't keep up after 6500 rpm. went VERY lean

mine wouldnt keep up after about 4500 or so.. 26# injectors = detonation w/ added power.

So what would be a good sized injector for a heads/cam stock bottom end build?

So what would be a good sized injector for a heads/cam stock bottom end build?



From the info I got and from what I've seen... FMS 42lb seem to be a good idea... (bought some last week) ... when u go bigger injectors you really need to be tuned for them... so may as well go big!

That Injector is too large IMO for stock displacement with our fuel pressure.

an FMS/SVO 36# injector will handle the majority of stock CID, NA buildups.

I ran RC 36#er in my 460 rwhp heads/cam car with no issues :)

SV0 30# works fine for mine :)

I have '01 Z06 injectors on the 383 stroker, I think they are 28#'ers. Working good so far! :D

30#ers will do the job, but phil wants to spin to the moon ;) I like the added safety up top. Id hate to loose an injector @ 7300!

What about using 28.8s out of an 02 car? Not enough for 400-450rw?
If I need bigger then I'll get bigger. Better safe than sorry.

Spin me to the moon.....apparently When I dynoed they used garbage weather conditions....I am making more HP than I orginally thought. I probably need 42s
Phillip

Too large an injector can cause metering problems under low and medium throttle conditions. The proverbial equivilant of driving a finishing nail with a sledghammer; it's just too damn big to get super fine control over. Idealy you would like to keep roughly 80% duty cycle at WOT and max RPM. That provides enough reserve yet still controls part throttle conditions fairly accurately.

I just put FMS 42lb injectors in my car.. almost tuned for non WOT driving (LTRIMS 3.4 now.. my next tune will have them at 0 to -1.6) and haven't had any driveability issues....

I decided that bigger is better... I'm going to keep modding my car.. and w/these 42s I'll be safe for a long time...

though 1 piece of advise I can offer ... 42lb injectors + Stock IFR Tables = bad ass sounding hehe (just can't rev past 1500rpm and car wont idle... and the tail pipe leaks gasoline)

Horist - I'm glad you got them in and running good. I tried the stock IFR table with mine also(by accident ;) ). The car would idle for a few seconds and die...WAY RICH!! :eek2:

I've also run the 42# SVO's on a 5.3L truck with NO driveability issues. I bought some bigger Siemens 57#(43.5psi) injectors for something I was going to do. It didn't happen but, I put them in the 5.3L anyway to see how they acted. Absolutely NO problems. They actually drive as well as the little stock truck injectors. :)

These computers are very good at part throttle metering and from my experience with the SVO 42#ers and the Siemens 57#ers these two injectors have NO problems running at very low pulsewidths. Heck, my idle pulsewidths are like 1.9ms with the 57#ers and everything is fine.

Personally I'd just go with the 42#ers and forget about injectors. :) N/A you'll probably only see around a 60% duty cycle on them but, that will leave room for a small dry shot. :D

Thanks for all of the responses. I'm leaning towards bigger is better incase I decide that I need a little NO2 to help me out.

Too large an injector can cause metering problems under low and medium throttle conditions. The proverbial equivilant of driving a finishing nail with a sledghammer; it's just too damn big to get super fine control over. Idealy you would like to keep roughly 80% duty cycle at WOT and max RPM. That provides enough reserve yet still controls part throttle conditions fairly accurately.





So if My injector duty cycle is hitting 100% just before where I shift 6600rpm then I need to upgrade my injectors?

TTT