Oh No another "what size injector?" thread
Thread Starter
Le Mans Master
Joined: Feb 1999
Posts: 9,922
Likes: 38
From: South Carolina
St. Jude Donor '03 & '05
Oh No another "what size injector?" thread
I am currently running up to 93% duty cycle at 6200rpm with 30# SVO injectors in my 396LT1. My redline, is around 6500rpm, and my wideband is showing now about 13.1 to 13.3 AFR. It was recommended that I run 42# Delphis, which seems quite a jump, but they are the experts. I know its not a recommend thing to run past 80% duty cycle. So, are the 40#'s to big, just right, or should I go with 36#'s.
I am running and maintaining 43.5ish fuel pressure up to 6300rpm.
I am running and maintaining 43.5ish fuel pressure up to 6300rpm.
Burning Brakes
Joined: Nov 2006
Posts: 1,102
Likes: 1
From: Portsmouth Virginia 396LT4 435RWHP/400RWTQ Best so far 11.26 @ 123mph
Steve,
I too had that issue with my 396 stroker and 30# FMS injectors running about 95% duty cycle at 43psi to get 12.6 AFR during WOT dyno testing to 6500 rpm. Ran them for a while but ended up changing them to 36# for that reason and retuning it. This is based on a 10.8 to 1 compression,230/236 on 112 cam and 195 AFR comp. head. I did make some bigger adjustments in my VE tables though to improve BLM's at Idle/Cruise because they were running at 108 to 112 in various BLM cells pulling a considerable amount of fuel out using 36#'s. I think you will find 42's too big.
Rick
I too had that issue with my 396 stroker and 30# FMS injectors running about 95% duty cycle at 43psi to get 12.6 AFR during WOT dyno testing to 6500 rpm. Ran them for a while but ended up changing them to 36# for that reason and retuning it. This is based on a 10.8 to 1 compression,230/236 on 112 cam and 195 AFR comp. head. I did make some bigger adjustments in my VE tables though to improve BLM's at Idle/Cruise because they were running at 108 to 112 in various BLM cells pulling a considerable amount of fuel out using 36#'s. I think you will find 42's too big.
Rick
Thread Starter
Le Mans Master
Joined: Feb 1999
Posts: 9,922
Likes: 38
From: South Carolina
St. Jude Donor '03 & '05
Steve,
I too had that issue with my 396 stroker and 30# FMS injectors running about 95% duty cycle at 43psi to get 12.6 AFR during WOT dyno testing to 6500 rpm. Ran them for a while but ended up changing them to 36# for that reason and retuning it. This is based on a 10.8 to 1 compression,230/236 on 112 cam and 195 AFR comp. head. I did make some bigger adjustments in my VE tables though to improve BLM's at Idle/Cruise because they were running at 108 to 112 in various BLM cells pulling a considerable amount of fuel out using 36#'s. I think you will find 42's too big.
Rick
I too had that issue with my 396 stroker and 30# FMS injectors running about 95% duty cycle at 43psi to get 12.6 AFR during WOT dyno testing to 6500 rpm. Ran them for a while but ended up changing them to 36# for that reason and retuning it. This is based on a 10.8 to 1 compression,230/236 on 112 cam and 195 AFR comp. head. I did make some bigger adjustments in my VE tables though to improve BLM's at Idle/Cruise because they were running at 108 to 112 in various BLM cells pulling a considerable amount of fuel out using 36#'s. I think you will find 42's too big.
Rick
Who tuned your Vette? Do you have your VE tables for viewing?
Melting Slicks
Joined: Aug 2003
Posts: 3,395
Likes: 393
From: Lakeville MI
Why not simply raise the fuel pressure to make your current injectors flow like larger injectors to bring down the duty cycle?
Here's a handy flow calculator I came across.
http://www.csgnetwork.com/fiflowcalc.html
Here's a handy flow calculator I came across.
http://www.csgnetwork.com/fiflowcalc.html
Thread Starter
Le Mans Master
Joined: Feb 1999
Posts: 9,922
Likes: 38
From: South Carolina
St. Jude Donor '03 & '05
Why not simply raise the fuel pressure to make your current injectors flow like larger injectors to bring down the duty cycle?
Here's a handy flow calculator I came across.
http://www.csgnetwork.com/fiflowcalc.html
Here's a handy flow calculator I came across.
http://www.csgnetwork.com/fiflowcalc.html
55psi only brings it up 3#'s. And my regulator wont go to 55psi if I tried.
Safety Car
Joined: Apr 2003
Posts: 3,793
Likes: 9
From: VA
I am currently running up to 93% duty cycle at 6200rpm with 30# SVO injectors in my 396LT1. My redline, is around 6500rpm, and my wideband is showing now about 13.1 to 13.3 AFR. It was recommended that I run 42# Delphis, which seems quite a jump, but they are the experts. I know its not a recommend thing to run past 80% duty cycle. So, are the 40#'s to big, just right, or should I go with 36#'s.
I am running and maintaining 43.5ish fuel pressure up to 6300rpm.
I am running and maintaining 43.5ish fuel pressure up to 6300rpm.
If the current tune is not close or there will be further mods, then the 42# leaves more headroom. Tons of people run 42# in LT1s with no problems, so they are not too big.
If I was paying someone to tune and they recommended 42# I'd probably follow their recommendation unless there was a good reason not to. And there isn't a good reason not to here.
Thread Starter
Le Mans Master
Joined: Feb 1999
Posts: 9,922
Likes: 38
From: South Carolina
St. Jude Donor '03 & '05
My tuner did a great job, there were just mechanicals on my side that needed to get fixed. Now that they are fixed I am trying to slowly tune things incrementely. \It was originally tuned for 30#, and I think 36# are in order.
Safety Car
Joined: Dec 2002
Posts: 3,655
Likes: 24
From: Charleston SC
Steve,
I have ran 36s and 42s w/o a problem, My recommendation is to get what ever is cheaper plain and simple. I run about 78% max Dc with the 36's but the y car ran great with the 42's as well and I was able to tune the car dead nuts with either of the two. Good luck and again get what you can find for the best price.
I have ran 36s and 42s w/o a problem, My recommendation is to get what ever is cheaper plain and simple. I run about 78% max Dc with the 36's but the y car ran great with the 42's as well and I was able to tune the car dead nuts with either of the two. Good luck and again get what you can find for the best price.
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Thread Starter
Le Mans Master
Joined: Feb 1999
Posts: 9,922
Likes: 38
From: South Carolina
St. Jude Donor '03 & '05
I am going to search for 36#'s. Hopefully I will have them by Christmas.
I got a fuel rail, the correct one for my 94 manifold. This will help too, as the injectors will go all the way down in their holes in the manifold.
I got a fuel rail, the correct one for my 94 manifold. This will help too, as the injectors will go all the way down in their holes in the manifold.
Safety Car
Joined: Apr 2005
Posts: 3,624
Likes: 431
From: Dale City VA
The FMS 36's are getting hard to find. However I just bought a set from Racetronix, I belive they bought Fords remaining inventory.
Will
Thread Starter
Le Mans Master
Joined: Feb 1999
Posts: 9,922
Likes: 38
From: South Carolina
St. Jude Donor '03 & '05
I am finding used ones, but they are wanting about the same for new.
Soon I will be selling my ported 93 manifold with 30#'s, then I will have some money to just get them, and racetronix has them for a fair price.
Soon I will be selling my ported 93 manifold with 30#'s, then I will have some money to just get them, and racetronix has them for a fair price.
