I spoke at length to Russ Collins of RC Engineering today about injector rating vs. injector flow. Many folks are confused about this issue, so I thought I would speak to the man himself.

He RATEs all of his injectors by the old school formula of lbs/hr or cc/min at 43.5 psi.

Jim Hall

I knew that 2 years ago, and at the time was told that 3 bars (43.5 psig) was the "industry standard" for rating fuel injectors. IMO, there needs to be ONE standard so when someone says "I got 30# injectors", it means: The injectors flow 30 lb/hr of gasoline at 43.5 psi fuel pressure. Otherwise, if it was not understood what pressure they were rated at eveyone would have to say something like: "These injectors flow 35.2 lbs/hr at 60 psig". Not rocket science.

So, is there a "new way" to rate injector flowrate?

GM expresses their injectors in terms of flow at 58psi instead of the old 43.5 standard.

Hell, I've never ever seen GM quote the injector flowrate @ pressue in any of their literature or in the Service Manual. Where have you seen it quoted?

The fact that the 2001 injectors were the same or different, was never the issue,

Not true ... there must have been half dozen threads arguing if the 01 and 02 injectors where the same. In fact Jim, you where the one who initially said they were smaller on the O2s if I recall correctly . Obviously now, we all know they are the same injectors since many board members called many dealers to verify the p/ns where identical.

I think for now we can put this to bed. Next time I need to make sure I am comparing in like units of measurement. I learned this in College Chemistry, but that was a long time ago.

I tried to explain all the injector flow rate vs. fuel pressure relationship way back in the heat of the discussion, but obviously nobody picked that up . I even showed a couple of examples of how the square root of the pressure ratio (flowrate correction factor for pressure) effected the injector flowrate. Oh well, I'm not a "tuner", so people tend not to listen to guys popping out of the wood work :lol: :d.

Thanks for the info anyway.


:cheers:

 

Still unexplained is the four Halltech T-1 SideWinder customers that have now made over 380 RWHP with the RC 34lb/hr@58 psi injectors.

Now check this out: We have a 2000 LS1 that made 337.7 RWHP and 345.1 RWT on the R&D Dyno, with me watching and about 30 other C5 guys last year. The engine had 900 miles on it. All pulls were in the 330s. Steve Cole himself was there watching.

Stock the car made 297.7 RWHP That's 40 RWHP, so far. Check out the list of mods and tell me where the numbers came from.

Mods on this car:

Halltech TRIC, MAG, Halltech 76mm MAF ends, LS6 Intake manifold; RC 34lb/hr@58 psi injectors, Halltech Ported Throttle Body, Halltech IAT sensor mod, TBCB, with stock exhaust except for titanium Z06 mufflers.

These injectors are the very same size we put on the STinger-R 470 Z06.

We now have Borla's headers, and the AFR1 onboard and need to redyno. This car goes sideways hitting second gear!

 

2000 Stock LS1 Engine and bolt on mods-34# injectors=397 HP

I tried to explain all the injector flow rate vs. fuel pressure relationship way back in the heat of the discussion, but obviously nobody picked that up . I even showed a couple of examples of how the square root of the pressure ratio (flowrate correction factor for pressure) effected the injector flowrate. Oh well, I'm not a "tuner", so people tend not to listen to guys popping out of the wood work :d.

I saw your post. I was always aware that the rating at 43.5 had to factor in the actual pressure. No mystery there at all.

If you go here: http://www.rceng.com/technical.htm#WORKSHEET


You can see that the actual fuel pressure is part of the formula. When we decided on the size injectors, we used this formula to determine the size to order. It was expressed in units @43.5 psi, which is the rating RC uses. I used that rating expression in all of my conversations with the forum. Remember, the 58 PSI static pressure has always been used in developing the injector size, but the expression is in units of measurement at 43.5 psi.

I now advertise and express everything in Corvette units or at 58 psi.

Our detractors jumped on this as a mistake on our part. It was not. The mistake occured in expressing the values in one unit of measurement, when everyone in the Corvette world is used to expressing it in the actual pressure vs. rated pressure. That started the controversy.

People saw this as an attempt to sell injectors, when in fact is was not. Luckily it turned out for the best, since the RC injectors appear to make more HP on the dyno than stock.

When someone can come along and duplicate our numbers with our intake and stock injectors, we will stop talking and selling injectors.

 

Halltech,

What do you think about proving the need for larger injectors and quieting the naysayers at the same time? Put a Z on the dyno making around 375-400 rwhp with YOUR injectors. This seems to be the biggest area of interest. Any less seems close enough to stock and more will have everyone agreeing larger injectors are necessary. Then, replace them with stock, do any relearns, etc and get it back on the dyno ASAP (in the same day) while conditions are the same. Any A/F tuning is fair game. Publish everything in SAE and it's done.

Maybe you could turn this into a friendly wager. Start an injector GP that hinges on your performance on the dyno. If you show at least X% (or Xhp) improvement over the stock injector with yours, the GP goes into effect. 25 registrations should make it worth your while, eh? I'll be number 1.

Chad

 

Halltech,

What do you think about proving the need for larger injectors and quieting the naysayers at the same time? Put a Z on the dyno making around 375-400 rwhp with YOUR injectors. This seems to be the biggest area of interest. Any less seems close enough to stock and more will have everyone agreeing larger injectors are necessary. Then, replace them with stock, do any relearns, etc and get it back on the dyno ASAP (in the same day) while conditions are the same. Any A/F tuning is fair game. Publish everything in SAE and it's done.

Maybe you could turn this into a friendly wager. Start an injector GP that hinges on your performance on the dyno. If you show at least X% (or Xhp) improvement over the stock injector with yours, the GP goes into effect. 25 registrations should make it worth your while, eh? I'll be number 1.

Chad

This has already been done three times. The fourth also had an underdrive pulley and BPP X-pipe and made 392 RWHP.

Nothing else to prove. Those that doubt our results will never purchase anything from Halltech anyway. At this point, I really don't care whether folks believe our results or not.

Jim

 

This has already been done three times. The fourth also had an underdrive pulley and BPP X-pipe and made 392 RWHP.

Nothing else to prove. Those that doubt our results will never purchase anything from Halltech anyway. At this point, I really don't care whether folks believe our results or not.

Jim

Hey Jim,

Just curious as to what exactly you attribute the gain to (and "bigger injectors" is not the answer I'm looking for ).

Are the cars you've tested running lean and thus show a need for the larger injectors? Are the stock injectors running at too high of a duty cycle and thus the PCM pulls timing? Are you seeing a timing increase (assuming you've run scans on the cars) by going to the larger injectors?

The reason I'm curious is b/c while I've got a lot less test time than you have, I've seen a number of cars run the stockers to very high duty cycles (we'd all agree this isn't optimum), but the injectors are still able to fuel the motor adequately (11.5-12.5:1 A/F ratios...so they're not running lean, even with AFR tweaks one way or the other).

So I guess bottom line is, even if a stock injector is a bit fatigued, if its able to supply the appropriate fuel to the motor...why then do you see increases in power just by swapping injectors (leaving the rest of the combo alone)? Could the PCM indeed be pulling timing out?

Thanks!

 

Some Injector Insight

So I guess bottom line is, even if a stock injector is a bit fatigued, if its able to supply the appropriate fuel to the motor...why then do you see increases in power just by swapping injectors (leaving the rest of the combo alone)? Could the PCM indeed be pulling timing out?

Thanks!

My theory on that would be because when injectors are ran in the 85%+ d/c cycle range, they start becoming vertually impossible to control correctly by the PCM commands. In fact (according to RC Eng), depending on the design of the injector, it will basically go static wide-open (ie, 100% d/c when the actual d/c hits 90~92%). Also, realize that as the d/c of the injector increases, there are more losses due to the fact that the open and close time of the injector (which is fixed for any give injector/PCM controller) becomes a larger part of its entire d/c.

Also, its unknown how these aftermarket injectors project their spray pattern compared to the stock injectors. I would think they where both adiquate, but without some nitty-gritty testing, it could be that the larger injectors have a superior spray pattern at the same fuel pressure but lower d/c which in turn makes for better power development with the same amount of fuel. It could very well be that a car with injectors running at the max edge will run richer because the injectors are toggling into the 100% d/c realm (at 90~92%) and this robs power due to a rich A/F. With larger injectors the d/c will come down into a very controlable d/c region, and that will make it easier to tune the engine for max power ... ie, very correct A/F throught the whole RPM range. Peak HP is always made where the injector's d/c is maximum (most fuel flow), so its best to have injectors you can really tune well to make the most HP potential of the engine ... not injectors that are in the "no man's land" of the control region.

:cheers:

 

so are the injectors different between an 01 and 02 Z and, if so, what are they?

Don

 

Re: Some Injector Insight

With larger injectors the d/c will come down into a very controlable d/c region, and that will make it easier to tune the engine for max power ... ie, very correct A/F throught the whole RPM range. Peak HP is always made where the injector's d/c is maximum (most fuel flow), so its best to have injectors you can really tune well to make the most HP potential of the engine ... not injectors that are in the "no man's land" of the control region.

:cheers:

I'm certainly not debating the reason behind running injectors at a lower duty cycle.

However, I'll just take my own car as an example. Until I put the MAFT on it was at 10.4:1 A/F ratio. Injector pulse width was over 21 mSec at WOT over 6000rpm. This is _awfully_ high. Then by leaning out the fuel trim with the MAFT, I got the A/F ratio right at 12.5:1. Pulse width is down to ~18 mSec.

The A/F ratio doesn't budge above 3000rpm...it's flat in the mid-12 range. Seems very controllable and repeatable.

For the sake of argument, let's say I throw in some RC Eng. 30s. Why, by themselves, would they allow more HP given NO other changes? The A/F ratio is already good, and it appears that the motor is being properly fueled.

If I add XX and XX mods to the car and it NEEDS more fuel...then I understand the reason for bigger injectors. That's not what I'm inquiring about, though.

Is somehow the 18 mSec pulse width telling the computer to reduce timing/power somehow...and if I installed larger injectors and got the p/w down, it would then increase power?

Just theorizing here.

 

Jim,

Thanks for the update - that squares with what GM, my tuner and someone who has actually flow tested these (stock) injectors told me. My Z06 is running around 370 RWHP (unfortunately I lost a few HP and gained .5 RWTQ with B&B headers) with your T1 and a MAFT. My tuner ran a scan on the injectors and it would seem I am well below 100% duty cycle @ WOT.

I have bought from you in the past, in fact ordered your new and improved velocity air filter for the T1 today. I believe new injectors would not make any improvement just yet, but if I can squeeze another 10-15 RWHP then who knows

Les

 

Re: Re: More information on Injector Sizing from Katech and RC

Jim,

Thanks for the update - that squares with what GM, my tuner and someone who has actually flow tested these (stock) injectors told me. My Z06 is running around 370 RWHP (unfortunately I lost a few HP and gained .5 RWTQ with B&B headers) with your T1 and a MAFT. My tuner ran a scan on the injectors and it would seem I am well below 100% duty cycle @ WOT.

I have bought from you in the past, in fact ordered your new and improved velocity air filter for the T1 today. I believe new injectors would not make any improvement just yet, but if I can squeeze another 10-15 RWHP then who knows

Les

Les,

If you have the information, would you mind sharing what your injector pulse width(s) are at WOT over 6000rpm?

This can be very valuable information to compare. Also, what is your WOT timing advance above 4000rpm?

Thx!

 

Jim,

I was unaware that the back-to-back testing had already been done. Since it has been tested AND proven beneficial, why is the merit of larger injectors still such a hot topic for debate?

Can someone please post a link to the back-to-back injector test(s)? This should clear up any speculation.

Chad

 

Re: Re: Some Injector Insight

For the sake of argument, let's say I throw in some RC Eng. 30s. Why, by themselves, would they allow more HP given NO other changes? The A/F ratio is already good, and it appears that the motor is being properly fueled.

If the injectors you have now are currently running at 90%+ d/c, then its possible larger injectors could actually yeild more HP because of the reasons I discussed above.

Besides, your car is slightly modded with 363 RWHP. so the stock injectors aren't quite at the limit yet ... but close I'd say. Remember, a good tuner defines the "limit" at an 85% d/c .... not 100% for the reasons I gave above.

As far as the PCM cutting back ignition timing at large injector d/cs, I couldn't say ... but its a good theory to investigate.

 

Re: Re: More information on Injector Sizing from Katech and RC

Jim,

Thanks for the update - that squares with what GM, my tuner and someone who has actually flow tested these (stock) injectors told me. My Z06 is running around 370 RWHP (unfortunately I lost a few HP and gained .5 RWTQ with B&B headers) with your T1 and a MAFT. My tuner ran a scan on the injectors and it would seem I am well below 100% duty cycle @ WOT.

So what was the injector d/c at 370 RWHP? And how did your tuner meaure the injector d/c (what type of tool/software?).

Method of measurement is not always accurate depending on how its done.

 

so are the injectors different between an 01 and 02 Z and, if so, what are they?

Don

From many previous threads, about 3 or 4 different board members called many GM part departments and verified that the injector p/n was exactly the same for 01 and 02 injectors.

Good enough proof for me.

 

WA 2 FST,

You have posed a rather interesting question, and I will attempt address it to the best of my knowledge. My experience in this area is based on turbo-charged engines but I don't see why the same logic shouldn't hold for n/a engines too. So here goes.

Most of the `power' mods people do to their cars are based on making the engine breathe better. These mods involve opening up the intake to let more air in, putting in bigger cams (to make it easier for intake and exhaust to pass though the engine) and then freeing up the exhaust tract. I will consider only the effect of improving the intake here.

So what really happens when you put in a higher flowing air-filter system? More air gets in, the PCM throws in more fuel (to maintain a nice a/f ratio) and you get more power. The bottom line is that you need more air and fuel to make more power. But there is a side effect to all of this. As the car's engine management computer (PCM) detects the increased air-flow, it moves to a different location on the fuel curve or curves (these fuel curves have been programmed into the PCM), which provides a more conservative timing. The main reason for the PCM behaving in this fashion is to protect the engine from catastrophic failure in the event the mas-air-sensor or some other component failing. The end result of the lower timing is that you loose power.

Tuners compensate for this by introducing another control element into the picture - an air/fuel computer (this unit may be known by different names but it essentially alters the mass-air signal going to the PCM). So now one can use the a/f computer and trick the PCM into thinking that less air is entering the system, although a lot more air is really entering the engine. This lets the PCM operate in the most optimal portion of the fuel maps and you get good timing and lots of power. But note that because you have tricked the PCM into thinking that less air is entering the system, it in turn will run the fuel injectors at a lower duty cycle, resulting in less fuel being sprayed. Less fuel means lower power. So in order to get more air, more fuel and still allow the PCM to operate in the optimal portion of the fuel maps, you stick in bigger injectors. Now these bigger injectors will continue to spray more fuel, although the PCM is driving them at say the stock duty cycle. The bottom line is that, with this form of tuning, you are striving to keep the PCM operating at the stock location on the fuel maps, while altering a lot of the parameters around it.

I hope I made things a little more clear. Please feel free to write me if you want a more in-depth explanation. On my previous car, I had replaced the stock T-25 turbo flowing 325cfm at 15psi of boost with a much larger one - the Frank 2, capable of 625cfm at 15psi. As a consequence the stock fuel injectors were replaced with much large 660cc ones.

Regards.
-Anil

 

So in order to get more air, more fuel and still allow the PCM to operate in the optimal portion of the fuel maps, you stick in bigger injectors. Now these bigger injectors will continue to spray more fuel, although the PCM is driving them at say the stock duty cycle. The bottom line is that, with this form of tuning, you are striving to keep the PCM operating at the stock location on the fuel maps, while altering a lot of the parameters around it.

The only thing I would comment on is that the PCM will have to be "re-mapped" to make the FI/PCM system operate like you have described. You just can't throw in bigger injectors and manipulate the MAF sensor signal to fool the PCM and expect it to provide the perfect A/F ratio throughout the RPM range.

Question: Does the LS1/LS6 use the MAF sensor and the IAP sensors for FI control at WOT?

 

Jim - totally off subject, but is this the same Russ Collins that built and rode the dual and triple fuel Honda motorcycles back in the 70's and 80's? If it is, I saw him race Terry Vance on the top fuel Suzuki the last time that Terry rode the bike at Orange County. The scariest race I think I ever witnessed; Terry claims that the bike put the fear of God in him permanently and thankfully, he parked that monster.

Rob

 

The only thing I would comment on is that the PCM will have to be "re-mapped" to make the FI/PCM system operate like you have described. You just can't throw in bigger injectors and manipulate the MAF sensor signal to fool the PCM and expect it to provide the perfect A/F ratio throughout the RPM range.

The fuel-computers I was refering to allow you to adjust the air-signal going to the PCM at multiple points on the rpm sprctrum. While not perfect, it does allow you to get a near optimal a/f ratio throughout the rpm range. The reason it is not perfect is because the PCM uses other factors to determine timing, and we are only attempting to control one or two elements here.

-Anil

 

Re: Re: Re: More information on Injector Sizing from Katech and RC

Hi Wes,

I called my tuner (Brad Brand - holds the world record for outlaw class 10.5 - knows something about cars). He said while scanning he only looked at peak, and on my car with A/F at 12.8 it got to 17.5ms. He says we can take it up the road tomorrow and scan for lower RPM but that is what it did at the top.

I (and he) are with you on this. If the car isn't running lean and is getting adequate fuel changing to a larger injector in of itself will have zero effect on RWHP. In fact as you go up in injector size at a given fuel pressure you don't spray (atomize) as well so you do not burn as cleanly, which is why GM does it this way. His calculations show that I am running 90% duty cycle, which is fine even for endurance racing (where running high duty cycle can create heat problems in injectors).

So while I believe Jim Hall (and I do) I don't understand how a car making 370 RWHP with the right A/F ratio benefits even 1 HP from a larger injector, unless as you say the PCM is calculating duty cycle and pulls timing out or something like that - I would love to know the answer.

Les

Les,

If you have the information, would you mind sharing what your injector pulse width(s) are at WOT over 6000rpm?

This can be very valuable information to compare. Also, what is your WOT timing advance above 4000rpm?

Thx!

 

The fuel-computers I was refering to allow you to adjust the air-signal going to the PCM at multiple points on the rpm sprctrum.
-Anil

Are you talking about aftermarket in series devices to reprogram the PCM via user inputs or complete aftermarket PCMs? I don't know if there is anything available like that for the LS1/LS6 yet. Anyone know?

The bottom line is that the PCM will have to be reprogramed (one way or another) anytime different sized injectors are used.

 

Are you talking about aftermarket in series devices to reprogram the PCM via user inputs or complete aftermarket PCMs? I don't know if there is anything available like that for the LS1/LS6 yet. Anyone know?

The bottom line is that the PCM will have to be reprogramed (one way or another) anytime different sized injectors are used.

That is right, I was refering to aftermarket air/fuel computers which allow the air signal going into the PCM to be altered, based on rpm, throttle-position, etc. I don't know if something like that exists for the LS6 (and that is why I said that I am speaking with my background in turbo-charged cars).

I do, however, hope that we have something something similar because it helps a lot when turning.

-Anil

 

From what little I understand, Jim has four cars that have seen the other side of 380 rwhp with his T-1 intake, an MAFT, and 30# injectors. Those with the same combo but w/o the 30#er's are seeing something less.

The answer to this mystery seems to lie among the 30#er's and MAFT working together with the stock PCM to produce a real world result much closer to the optimum.

Does anyone know if the PCM can "see" the injector's duty cycle for purpose of controlling it? Why would it even care?

It would be helpful to see a couple of more results with the 30# injectors with an MAFT to corroborate the results that Jim has seen with the four that he's tested so far.

If it works, why ask why? (so long as A/F remains in a safe range).

 

Jim Hall -- how do you "reprogram" the PCM fuel maps when you throw 30# or larger injectors into the LS6? Is it all through the AFR1?

Is the AFR1 just a MAF sensor signal trimmer device?

 

Jim - totally off subject, but is this the same Russ Collins that built and rode the dual and triple fuel Honda motorcycles back in the 70's and 80's? If it is, I saw him race Terry Vance on the top fuel Suzuki the last time that Terry rode the bike at Orange County. The scariest race I think I ever witnessed; Terry claims that the bike put the fear of God in him permanently and thankfully, he parked that monster.

Rob

That's him. He now has one less ear from a C5 accident in which his front end actually broke sending him into a tree.

He is probably the most knowledgable person I have even met on fuel injection and engine building. He was building blown motorcycle engines when I was in High School.

Larger fuel injectors on their own do nothing to improve the performance of the engine.

For those that have been following the progression of our 2002 Z06, you will remember that we made 367 RWHP (+16.2 RWHP/+19.4RWT) with just the T-1 Intake.

After we ported the throttle body, and the injectors, we returned to the dyno and could not manage over 369 RWHP. The injectors alone actually took some power away, since they made the car run slightly rich at WOT. 1-19 showed -2 to -6 LT Trims.

I decided to use our AFR1 to recalibrated (fool the PCM) by leaning out the a/f mixture in the high frequencies. One click only on the AFR1 (2%) and the car felt like it had a supercharger on board.

Back to the dyno, and 381.2, backed by three more pulls within 1 HP.

Three days later we installed B&Bs and went back to the same dyno again. 384.2 RWHP. The actual RWHP was 395 RWHP, but the correction factor pulled 3% or so out of the pull.

Since then John Wu and Sean Reis have installed the same mods with very similar results. John Wu hit 383.5 RWHP, Sean 380.1 RWHP. (Sean had not installed the some of the T-1 SideWinder mods at that point).

What is interesting is that the computer likes the combination of the AFR and the injectors.

We did three months of testing to come up with this combination. I am not really sure why it works so well. Mods are very strange in that many times, a mod needs one or two other mods to come alive. A bigger cam is not worth much if the heads can't flow the numbers, and the heads and cam can't make things happen without a less restrictive set of tuned headers, and so on.

This is why we sell packages and not a full range of parts. The LS6 is a genuine muscle car, which is begging for more air and fuel. We just like to make that happen.

Jim