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Discussion Starter · #1 ·
If you do not mind, I would like to know your combo, FP, chip, ET/MPH and weight w/driver. Trying to determine just how far (HP-wise) you can go with these injectors.

I know raising the FP will cause the injectors to flow more, but what does that do to the inj DC?
 

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50's are good, SAFELY, to 425-450 hp. More than one has pushed a Regal to high tens, but, I consider this more than fool hardy if one believes in science.

Raising fuel pressure increases flow by the Square root of the new pressure divided by the old pressure-in theory. Takes a pretty big pressure jump to make much difference if this is true.

Turbo cars have a bsfc close to 0.6 lbs/hp altho many use the n.a. number of 0.5 lbs/hp when computing hp potential. Most injectors seem to be pretty much all in at 80% duty cycle even if the pulse width is increased to maximum.

Here is a site with more tech info and a java calculation. http://www.rceng.com/technical.htm

Remember that weight is just as important as hp when it comes to the final product so that a 2500 lbs car is a lot easier to get to the tens than a 3500 lb car. :D
 

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Discussion Starter · #3 ·
Steve,

your response is exactly why I am making this post. I see an implied rule-of-thumb in the TR world that says: max HP supported = Inj size(#s) * 10. I have seen a couple of claims that indicates folks are making 500RWHP with these injs using a popular and fairly accurate HP formula. I myself am making 485 based on 2,750lbs w/driver and the timeslip in my sig.

Now, here is where it gets wacky and confusing for me. I normally run up to 95 inj DC (as per DS) and have even seen 100+% with not a trace of a problem. MOF, when I ran that number, I had a fairly heavy dose of C16 in a mix and the car went thru the traps at 1450* on the EGT with 0 knock. That was on pos C with the standard M/E. Conventional thinking says I could have dropped down to pos B or run more boost safely!! Is there something unique about the MSD50s that allow folks to run like that?

This is all leading up to making a decision on what inj to upgrade to. I like the idea of the 57# low-impedance but if the MSD50s can perform at extremely high DC and the 57#s not as well, I am screwed from the get-go. Only other option is 72#s and the PITA of shipping off the ECM for the mod.
 

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correct me if I'm wrong but don't the new Z06's have 28lb. injectors? maybe it's 32 but that still almost double the injector and that model car is making 405 flywheel and maybe 350-370 at the wheels? i think that's also a conservative number...just like GM rated our cars. :D

is that 425hp at the wheels Steve? :confused:
 

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I have said it before and I will assume this until someone proves me wrong. I don't think you can trust the Injector Duty Cycle reading in DS with the MaxEffort chip, or any aftermarket chip for that matter. It's probably a calculated figure. Maybe it would be accurate if you had the TW set to 'F' (the richest possible setting), but the chip obviously fools with the fueling so I take those readings with a grain of salt. Another good example of this is the AF ratio reading in DS. It's a calculated value and has nothing to do with reading from any of the sensors.

I say the 50's are fine until you are running on position 'F' and then you are running out of fuel. To make matters more complex, you have to factor in where the 'Fuel In' (position 'A' I think) is set. Only person that can clear this up would be Steve Yaklin. powersix
 

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At 3870 with driver my trap speeds are 122mph. This equates on the HP calculator to 547HP. My 50lb injectors are at 85% DC @ 20lbs of boost. Fuel pressure 43lbs(static). I feel the 50's will get me in the ten's with no problems after I clear up a few gremlins.
 

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yeah...rear end.

If one uses .5 bsfc and 100% duty cycle, then it is simply 2 x 6 cyl x injector flow. Therefore 50s would be 600 hp. Everyone likes to use this formula because it is easy, but, it ain't necessarily right.

Lots of argument on whether injectors behave properly and continue to deliver past 80% dc.

Not as much argument over bsfc. I use .6 and some of the gurus use .55. I think this depends upon combo. The guys that run really fast have a higher bsfc than the moderate combos. You can see evidence of this in the A/F ratios. Faster guys are in the lower 11s A/F while us mortals are in the higher 11s A/F-wise. Near stock may be around 12-1.

Factory used 28 lb injectors and put out 250 or a bit more at the rear end when we cranked the boost and tried to get enuf fuel to them.

Woody, I think, has been 10.77 on 55s with a double pumper in the tank and seems to have been all done. That would imply something like 540 hp.

Me, I think it is risky to run past 80% and believe that you are getting more fuel than you were at 80%-I think it will be erratic. I like using 80% and .6 and knowing that I have a margin for error.

Might as well match them up for the max of the turbo potential, tho I believe the turbos are generally overated.

Yah pays your money and takes your choices. Some claim to have gone Tens on a TA49 and others claim to have run mid 11s on the 30# greenstripes....I don't think most of us are that good. :D
 

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I am with Steve. It makes more sense to build beyond your needs, and tune to your goals. There is always the "What If?" train of thought, which can be less profound with the correct preparations.

I would stick with your 50s if you like them, and run a 7th injector system. Get a 160# injector run it at static (boost ON triggered of course) and you have yourself a 76lb/hr system, with the enjoyment of your 50s and a stock ECM.

Most people chuckle at the fuel system in my Buick, not because I am running stock parts... but, because it has the capacity to go high-10s, and I am running 13s. I don't think twice about fueling issues.

HTH,
 

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NCBuickGN:
Scottie-GNZ:


Only other option is 72#s and the PITA of shipping off the ECM for the mod.
Got a fresh ECM from www.gmpartsdirect.com (3 days)

Shipped to Bob Bailey for low-imp mod (back to me same week)

10 days total, and no more concerns about DC!

Priceless! :)
The low impedance mod matches the ecm drivers to the injectors (low imp injectors) and prevents ecm overheating from excessive current draw. It also supposedly makes the pulsewidth control more crisp on the injector end.

It will not improve injector control past 80% dc as far as I know. :)

With regard to sizing, it's kinda lousy economics to go from 50 to 55 or 57# injectors. Not much bang for the buck. Take it from a guy that has had 36, 40, 42.5, 50, and 75# injectors. :D

I would go straight to the 72/75# injector, and if you want to spend some more money that is burning those holes in your pockets, go mafless. Unclutter that engine compartment, so to say! :D

But, I think you said you were running 1450s for egts?, Tw that thing down, or take some out of offset as you are running too fat. You have more left. 1550-1625 is probably more like it.

I bet Ed is running in that range with his 50s. Get the latest chip with the X-factor and add some fuel right at the end.

The pulse width in DS should be right, but, altho some seem to have implied that you can run past 100%, you cannot. It can calculate a time and command it but effective max pulse width is a function of rpm. The higher you turn the engine, the smaller the effective max pulsewidth will be. In other words if you comand the injector to be open for one second, that obviously cannot happen at 5000 rpm...not in sync with the crankshaft as you would have about 40 intake strokes while the injector was being held open.

Now, combo and operating conditions really determine bsfc. The average engine seems to be around .5#/hour. A high rpm prostock engine might be between .35 and .40 #/hr. Forced aspiration engines tend to be .55-.65. Unless you have the engine on a dyno and measure fuel consumption, you really don't know. With all the effects of various parts combinations, all you can do is use history and guess.

If you have injectors, then you can use egt and knock to find the limits. Leanest is not always fastest. How many times have you heard popping at the top end and yet not a trace of detonation? Probably more than once on a faster car. Good octane may prevent detonation even though the engine is lean popping. Give it more fuel and it often will run faster.

At 1450 egts, I would say you are running quite rich and have not used up the injectors. Lean it down, pulsewidths witll come down, and the car will probably make more power. Keep leaning it and it may not detonate, but, it may slow down. Trial and error. :)
 

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I was referring to this statement.

"10 days total, and no more concerns about DC!"

Guess I missed something?
:)
 

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running on the edge with injectors is my favorite pastime!

however, I feel my 3725 lb car will easily run 10.6's with 55's...I haven't had a decent 60' time since I put the ATR headers on (header to turbo leak........)

if ya look at Lubrant's chart, I am right there...I used to think that chart was wildly optimistic, but as it turns out, if the injector gets enough volume (better or more fuel pumps) it works out....I run my ME at the default offset in position C and never get a burp

all that said, get 72's (with a pump/pumps to support) and never look back

I'll be going there and MAFless this season
 

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Scottie-GNZ:


Only other option is 72#s

and the

PITA of shipping off the ECM for the mod.
Yup, had to take the entirety of Scotty's quote, including the reference to 72# injectors.

The post hopefully encouragingly pointed out the ECM mod (required for the 72s) was not necessarily a PITA, & once completed (and the 72s installed), there would likely be no further reason for concern over DC at current/known power levels.

(Hopefully, no one on the boards is likely to presume only an ECM mod ALONE (without a concommitant injector upgrade) would have a beneficial effect on inj. DC.)

HTH :)
 

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:)

no, I thought you meant you did not have to worry about duty cycle after the mod. Anytime one hits 80% with, or without, the mod, you have to begin to worry as the mod does not allow the injector to perform any better past past 80% than it would without the mod.

I think what you meant was that bigger injectors would allow him to run at lower duty cycles.

:)

I think he can run a bit lower as it is with the current injectors if he leans the car down and raises the egts.
 

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11.44 @ 117 at Bowling Green this year.1.51 60'times, 50lb injectors, 53 turbo, Champ. iron heads 206 roller cam, F.A.S.T., shifting at 5700 I'm sure there is another 2 tenths there when I lower the shift points to around 5200. injectors at 92%DC with 23lbs boost, I don't think car is going to go faster than 11.20 ish with these injectors..But I'm happy as can be with the car and the way it drives. I use the heck out if it on the street with the a/c on and SMC alcohol. Ya just gotta love these cars!!
 

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Steve Wood:
:)

no, I thought you meant you did not have to worry about duty cycle after the mod.
Nope.

Although at one time (14+ months ago) I confess to being "dumb" enough to have trusted that all TB.com advertising vendors were honest/honorable (and subsequently dealt with a lying thieving sleazoid slacker), I would never be so uninformed as to suggest that the low-imp ECM mod be done as an independent mod.

So, that's at least 2 things I've learned from the boards, eh? LOL! :)
 

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11.15 so far with the 50's, but that doesn't count in a 2900# car :)
 

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Sure it counts! It's all apart of the equation. Easier to go fast with light weight than a lead sled!
 
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