View Full Version : Time for bigger injectors?

04-04-2003, 09:51 PM
As of now I have a stock MAF, 75MM TB, Ported plenum, 5% pulley, a raised top on its way, full exhaust with no cats, and nitrous is being put on as we speak. I have a ZEX nitrous kit and I am using a 55 shot. I have stock 30lb injectors. Do you think i'll have enough with the 36lb....? he nitrous kit says that it works with stock fuel system and injectors, but i dont want to lean out. I also have a 255lph pump to supply enough fuel. What should I do?

XR7 Dave
04-04-2003, 11:17 PM
Spring for some 38's and a 76MM C&L. You won't regret it. Also hook up your octane plug to a switch so that when you activate your ZEX it retards the timing 4 degrees. Your engine will thank you.

04-05-2003, 12:34 AM
the what and the what now???? WHere is that? The ZEX already bumps up the fuel pressure. I wonder if i'll be ok with the 30lb for now...untill i save up around 350 for new injectors..unless someone has a set to sell.

04-05-2003, 12:37 AM
i dont see any gain with a 73mm MAF. You are only gain 3mm in total diameter, thats not much at all. Even a 76mm....you are only gaining 6mm total. PLus they are pretty expensive for just a base with no electronics. I'd rather spend the 165 bucks other places.

04-05-2003, 12:40 PM
here are some 36s

ebay link (http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&item=2409625099&category=33554)

XR7 Dave
04-05-2003, 01:11 PM
Don't mean to sound arrogant, but if you don't understand what I just said, and if it doesn't make sense to match your MAF to your TB, then you really shouldn't be messing with nitrous. Just my .02.

As for the C&L 76(I never said anything about a 73mm BTW), first of all, your stock diffused 70mm MAF might flow 500-600 cfm, whereas the 76 flows almost 1000. The 76 is good for at least 375rwhp(without nitrous), so there would never be a need to upgrade again. 6mm is a HUGE improvement giving nearly double the airflow. The C&L also gives you the ability to change injectors at will, something your stock one cannot do at all. Since you have already sprung for the 75MM TB, I just assumed that logic and money would follow for you to match it with a comperably sized MAF that would allow you to run bigger injectors. My bad.

Regarding the injectors, you can find 38's for under $300 from a number of sources. However, unless you see benefit in a larger MAF, then don't bother with injectors either, because that will force you to either get a new maf or a chip.

Your car has an octane retard plug that can be connected to a switch retarding your timing during nitrous use. This will add a margin of safety against detonation under nitrous use which would most certainly result in a scattered engine. It is found next to the diagnositic connector under the hood. Pulling the plug retards WOT timing by 4 degrees. It can simply be wired to a switch either electronically activated by the nitrous switch or on a manual toggle.

Good luck. :)

04-05-2003, 04:46 PM
i know injectors and a new MAF would be nice, but doesn't 170 seem a little much for an aluminum hole? If i can find for for a good price i'll get that and also get new injectors. Would i be good enough to use the 36lb injectors from a later model SC, or would that not be enough and i'd have to jump up to the 38lb??

XR7 Dave
04-05-2003, 05:22 PM
I paid $135 for my 76mm brand new. I don't know how much cheaper you think it should be. If you were real creative, I suppose you could make one. 76MM is almost exactly 3". It's almost worth a shot. Maybe I should try it. :)

As for injectors, the newer SC units will still require a new MAF, so I guess why not get an injector big enough to handle any future mods? To answer your question, they would probably do ok, but not really worth the trouble.

04-05-2003, 08:01 PM
alright then...thanks for the help...now i'm looking for 38lb injectors and a new maf so i can get this car back together and try this nitrous.

04-05-2003, 08:37 PM
Is there any way that i could use any 75 or 77MM for a Ford? I see alot of mustang MAF's for cheap. I can get a 77mm bullet MAF for around 90 bucks. My question.....can i use that on mine? Is the only difference the size of the sampling tube? So if i got a sampling tube for 38lb injectors, could that MAF work for me even though its made for a newer style stang?????

04-06-2003, 04:01 PM
or....could i cut that difuser out of the stock one and then drill out the hole for te sampling tube...just like the instructions on MN12performance.com???? Or how about an adjustable FPR. Could I use that to bump up the pressure, making the injectors flow more?

04-07-2003, 02:17 AM
Decide if you are going to change injectors.

Now buy MAF calibrated for said injectors.

Buy either C&L and correct tube or get a Pro-M.

If you buy a Pro-M used it will MOST LIKELY be calibrated for a 5.0 V8. Just for an example: stock injector size for a SC will use a Mustang COBRA 24 lb calibration. So if you go 38 lb injectors and try and buy a used Pro-M you are in trouble. You will need to find out what calibration would work or get it recalibrated by Pro-M for about $125. So C&L looks alot better at this point.

Do a lot more reading and learning about nitrous before you jump into this. Unless you make real good money at 17 and have a spare car think it over.

04-07-2003, 12:26 PM
Stock late style injectors are really only 34.3# not 36#

Stock MAF (55mm older style or 70mm newer style) flow 990 kg/hr at 4.85V straight from the MAF transfer function in the EEC. My 76mm C&L with a 36# tube would handle ~1200 kg/hr and with the 50# tube can handle about 1500 kg/hr before it pegs the sensor. I was pegging the meter (hitting 5V) with the 36# tube so I had to go to the 50# tube to lower the voltage reading.

With the stock MAF and NOx, I'll bet you'll be real close to pegging the meter. That's usually a very very bad thing. If you're lucky, it'll set codes. If you're unlucky, it'll go lean and blow up in a relatively big hurry. NOx does not like being lean... at all.

P.S. I agree with everything Dave said. :)

04-07-2003, 02:44 PM
but what about a FPR? I guess i wont mind getting a new MAF, but i rather not get injectors. Can i use an AFPR to raise the pressure, thus providing more fuel into the injectors?

XR7 Dave
04-07-2003, 06:35 PM
Couple problems with raising fuel pressure.

1. The adaptive nature of the EEC will tend to dial out the gains from increased pressure. This is not a reliable way of compensating.

2. As pressure increases beyond a certian limit, your flow will begin to drop off. If you raise the baseline pressure, then add boost pressure, then add the additional from the ZEX kit (it uses higher pressure to get you the additional fuel for the nitrous), you will be getting pretty high which taxes both your pump and injectors. I wouldn't suggest trying this.

You could mod your maf according to the instructions on MN12 Performance, but that won't help you run bigger injectors.

If you want to get a Mustang MAF, that is fine, but you need to make sure that you get the right calibration. You need to take the Mustang calibration injector size x 8/6 to see what injectors it is compatable with on a 6 cyl.

For example: 24 x 8/6 = 32 This is pretty close to the stock injector on an SC.

Another example: 30 x 8/6 = 40 This is close to 38's which is what I have on my car. Mine is a Pro M calibrated Cobra30 and it runs perfect.

Unless I am wrong, nitrous on it's own doesn't draw more air than when the motor is off the bottle. The additional air comes from the nitrous itself.

And what Steve is talking about with using different sample tubes to get more airflow capability is only valid if you have the ability to tune the EEC, which you don't.

As for getting more fuel by raising pressure, that is exactly how the ZEX kit works every time you kit the button. It does it for you. Technically you don't need to do anything, just like ZEX says.

But getting back to the original question, you asked if you needed bigger injectors. I said you should get some. You don't have to, but you should. Now you are saying that you don't want to get new injectors. The whole discussion about MAFs was centered around getting new injectors. If you choose not to get new injectors, then don't worry about the MAF at all.


04-07-2003, 08:06 PM
GET THE INJECTORS. you might as well and it will be a lot more safe. If you do, make sure you get Bosch injectors. I've heard (this may or may not be true) that the bosch can hold up a lot better to high fuel pressures than the lucas can. Also, are you having some one else install it? how much they charging you? Its really simple to do, i put mine in in about 4 hours.

Any more detailed location of where that octane plug is? I think i am going to wire that up for when i turn it up to 75 shot.

04-07-2003, 09:14 PM
you guys have been a huge help. I think the safest way is to get larger injectors..which in turn will lead me to get a new MAF. I do all my work myself, and since the blower is off now....it'll be a peice of cake to change the injectors. Will the new injectors....should I go with an AFPR. I'm not sure if the stock one is ok to use or should I get a kirban with the 38lb injectors.
I would also like to see a pic of where that octane plug is so i can use that when i run the nitrous. Can i flip that switch at the line at the track and turn it off when i'm done? Will it mess up idle or the mixture at the start? I just want to make sure it only works at WOT, and doesn't effect my lauch before the nitrous kicks in (halfway down the track). So it wont bump up the timing at idle and half throttle....only full throttle??

04-08-2003, 12:38 AM
Originally posted by XR7 Dave
Unless I am wrong, nitrous on it's own doesn't draw more air than when the motor is off the bottle. The additional air comes from the nitrous itself.

NOx on it's own won't increase won't increase airflow. HOWEVER, it will make the motor rev much faster and extend (for lack of a better word) the powerband of the motor. So, if it could rev to say 5000 before power dropping like a stone, it may now like to run to 5500 before it falls hard. That extra 500 is where it would lean out.

And on the injectors, may I recommend these
Accel 40's (http://store.summitracing.com/default.asp?target=search.asp&type=bysummitpart&searchtype=both&part=ACC-150640) or these Accel 36's (http://store.summitracing.com/default.asp?target=search.asp&type=bysummitpart&searchtype=both&part=ACC-150636)

I run Accel 48s in mine and they seem to work pretty well. The 'true' aftermarket 36's would probably be ok for you. Although 38 or 40's give more room to grow later on.

04-08-2003, 11:52 AM
Originally posted by BlackbirdSC
NOx on it's own won't increase won't increase airflow. HOWEVER, it will make the motor rev much faster and extend (for lack of a better word) the powerband of the motor.

What Dave said was that NOx provides it's own increased air. That's how it increases HP so much, NOx is it's own source of combustable oxygen so you don't need to flow more air into the engine to gain from NOx.

So you're right, NOX doesn't increase airflow.

04-08-2003, 05:31 PM
Dave, where did you find that new MAF for $135?

XR7 Dave
04-08-2003, 05:52 PM
C&C Performance (http://cncperformanceparts.com/tbird.htm)

This is where I got mine. Guess they were on sale. Still $145 ain't bad, and they will get you the right sample tube.

Summit (http://store.summitracing.com/default.asp?target=search.asp&type=bykeyword&searchtype=both&part=mass+air)

This is the Vortec 80 calibrated for 30lb injectors on a Mustang should work fine with 38's. $149 is not bad.

04-08-2003, 06:15 PM
Thanks Dave.

04-09-2003, 12:02 AM
so the stock FPR will work on with the bigger injectos and the fuel pump...as well as the zex kit when it bumps it up???