5th injector vs extra injector per intake runner

[calichtr]

I am fairly new to all this so hopefully I am not saying something dumb.

I have heard some people say the 5th injector approach often ends up with one end cylinder richer than the other end which will mean the rich end cylinder will end up rich since you'll knock if you let the leaner end go too lean. This would seem to reduce HP since you have to run the rich end richer than optimal.

I have also heard of some intake manifolds that have spots for an extra injector per intake runner which allows you to tune each cylinder separately... although I am not sure how :confused:

Do you have any plans to implement something like this?

[Tom @ Fast Forward]

For the better part of a century, cars ran off of a carburetor. A version of single source injection of fuel into the intake manifold and run to multiple cylinders. Some of those vehicles set land speed records, 1/4 mile times and pretty decent Indy laps. Then we progressed to Throttle Body injection where one injector was used into the base of a throttle body and back to the various race tracks we went. Then emissions became a great issue and manufacturers went to all kinds of new technology to decrease emissions and along came multi-port injection and the like.

A long time back GM did a study and determined that a single source of injection could have as much as 10% distribution error in a smooth runner intake system. In our case, 90% of the fuel comes from the main injectors and is distributed as well as Mazda could make it happen. The last 10% comes from the single injector and is injected into the turbulent air at the outlet of the blower. This will definitely be better than the smmoth intake runner system that GM tested but, assuming it is as bad as 10%, then some cylinders could get 99% of the appropriated fuel and others could get 101%. This could mean that some cylinders could run at 12:1, for example and others at 11.88 and others at 12.12. I would venture to bet that it would not be any closer if you used four additional injectors with one at each cylinder. We have run tests at the dyno and could not measure any significant difference in temperature of the four exhaust runners.

At the power levels we are running (220WHP and below), I do not forsee switchig to a four additional injector system. Putting the four injectors in a manifold for a high horsepower hotside system is OK because you can use other methods of cooling the intake charge air (like an A/A IC). With that all you need is more fuel. If 12:1, for example, was all you needed to make the engine run, we would not need A/A or A/W intercoolers or liquid evaporative cooling like injecting water, water/alcohol, fuel or other liquid into the air stream prior to the cylinders.

I am successfully running well over 15PSI boost with 280cc main injectors and a fifth injector properly located as to add fuel and cooling. If water burned, we would have used that. ;)

There are two problems that I see about running the four extra injectors in the intake runners right at the cylinder. One, they are typically run with an Additional Injector Controller (AIC) like the SS. These are map/RPM based and not linked to the individual cylinder injectors. That means that if you inject twice per revolution, you are squirting at a closed intake valve three times and once with it open. That does not seem efficient to me? As they are so close to the valve, the fuel does not get a chance to be useful for cooling the air as it would if it were further away. Mazda used to do that with the 90-93 Miatas where they batch fired the injectors like the spark plugs. In that case, they would squirt once with the valve closed and once with it open. By 1994, they changed that to sequential fired and only fire while it is open. It was not a bad thing and caused no harm but sequentially firing did help emissions.

Keep in mind that single source injection like TBI and Carburetors where 100% of the fuel was single source provided went by the wayside not because they were a problem and engines blew up if you pushed them hard (still a lot of old muscle cars working hard at Firebird on Friday night :)) but because of emissions. If one were to worry about the simple 'lean' fuel of 12.12:1 being an issue, all you have to do is run the A/F at 11.8:1 and all cylinders would be 12:1 or better.

Hope that helps?

[FormerDatsun510Man]

I agree with a lot of what you are saying Tom, but a couple technical notes:

First, the amount of fuel coming from extra injector(s) on a 220+rwhp Hotside is not 10%. It is more like 30% for the 220rwhp power level. It becomes even more weighted at higher and high power levels. For example, at the 240rwhp power I am running:

4 x 245cc stock injectors at 70% duty cycle (estimated, see attached spreadsheet)
4 x 270cc extra injectors at 50% duty cycle (according to my Split Sec Map)

Total Fuel = (4*245*.7) + (4*270*.5) = 1226
Extra Injector Fuel = 4*270*.5 = 540
Extra Injector/Total Fuel ratio = 540/1226 = 44%

So at 240rwhp I am looking at the extra fuel accounting for 44% of the total. This is one of the reasons I believe a single extra injector is not the best solution for higher powered setups. The threshold IMO is around 220rwhp, because this is when the percent of extra injector fuel becomes proportionally pretty high.

The second point I disagree with relates to the fuel distribution with the stock Miata intake manifold. It was only designed to flow air... not fuel. It differs greatly in flow design from a carbureted manifold (or TBI manifold which really is a modified carbureted manifold). The Miata manifold, and most MFI manifolds are closer to a log style manifold. When one puts an extra injector in this manifold, it will be put at the front. However, the distance the fuel will have to travel will be quite close to cylinder #1, with the path being furthest to cylinder #4. This differs quite a bit from any carbureted manifold that I have been familiar with. On my Datsun 510, the downdraft manifold had very close to equal length runners to all 4 cylinders coming from the carburetor barrels. It basically looked like two Ys, where the end of each Y fed two cylinders (one fed 1&2 and the other 3&4). Even in that case, I recall there had been tests done that showed the outer cylinders (1&4) got a bit more fuel than the inner ones. Likewise, with sidedraft SUs, it had a single Y basically going straight from each carb. That would probably give fuel distribution as good as MFI. Similarly, with many V8 stock and performance intake manifolds designed for carburetors, one will see much attention is paid to the flow path. Take for instance the differences in single plane, dual plane and tunnel ram style manifolds. They all have their benefits/virtues, and they have attention given to the distance the fuel has to travel from the carb(s) to each port. It is a bit different than taking a intake manifold designed for MFI and adding a fuel injector in the front of it IMO.

Note, that these comments on extra injector vs one in each runner applies to the stock intake manifold. In the case of the Coldside manifold it is a different story because that manifold is designed for more even flow due to its plenum and also that you have the extra injector right at the outlet of the blower for good mixing from the turbulence there. Likewise, with the R4 manifold, it is closer to a carbureted type manifold, so placing a single extra injector in the downpipe to it would probably behave like TBI and yield pretty good fuel distribution.

Of course, all this is theory. To really quantify it, we would need to devise a way to test a/f ratios, temps, etc. at each cylinder and experiment. One real data point that I do have though is back in the old days with the original BRP setups they used no Powercard, but only 2 extra injectors. My setup went from 195rwhp to 207rwhp, with no other changes but simply the addition of the Powercard and then reducing the fuel coming from the extra injectors. The a/f ratio was the same 12:1, but the power went up 12rwhp. Since the only difference in the two setups would be where the fuel is coming from, I think likely this was showing the differences and effect of fuel distribution. Likewise, it would stand to reason that the less fuel coming from the extra injector (on a stock Miata intake manifold) the better the fuel distribution.

Bill

[FormerDatsun510Man]

Forget the attachment! I can't upload an Excel file format!!! grrrr LOL

Bill

[Tom @ Fast Forward]

I dumped the duplicate post for you. Too bad Excel wont let you 'save as' jpeg. :(

[Tom @ Fast Forward]

Well, my point was really about the problems, or lack there of, for single point of injection. IE. Carburator or Throttle Body Injection. I was trying to infer that it was the best but that the distribution must have been pretty good or a lot of people would have blown engines back in the days of my childhood with big blowers and carburetors. :)

My stock kits with the 5th injector have the 5th injector running at a max of 25% and typical of 12% (halfway). The 5th injector is 480 cc or basically = to two stock injectors. Running at the typical 12% = ~58cc/min. The main injectors are running at about 80% or 0.8 * 240 * 4 = 768. 58/768 = 7.5%

Maybe the Coldside is just more efficient? ;)

Now, if you compare my base 200WHP kit to your 240WHP kit, you need 20% more fuel. As your main injectors are running 10 % less than I do, I can see where you are running the extra injectors a lot.

My second point was that pulsing fuel at the closed intake valves 3 out of 4 pulses (I assume you have the SS set for 4 cylinder 4 cycle?) doesn't do much but possibly puddle the fuel at the closed valves. When the valve finally opens, the fuel is not atomized very well and may require more fuel to make the same 12:1. Remember, the wideband O2 sensor is reading how much air is consumed, not how much fuel. If there is unburned fuel, it will not register as rich. A good example is a misfire. With a misfire, all of the fuel goes into the exhaust pipe but the O2 sensor will read lean, not rich, as the air was not burned either.

Just guess as we really don't know one way or the other. As I said earlier, we have measured the temperature of the four exhaust runners when on the dyno and saw negligable difference from one to the other so the distribution must not be too bad. On my coldside running well over 15PSI on 91 octane in AZ heat, it must not be too bad either or parts would have popped out by now. :)

With respect to A/A intercoolers, that video of the boys at BRP drifting the customers car in the parking lot until the piston exited out the passenger side is one example where I would much rather had E-Cool. A/A ICs don't do much when there is no forward motion. ;)

[Mark]

Anywhere we can see this video??? :)

[FormerDatsun510Man]

I dumped the duplicate post for you. Too bad Excel wont let you 'save as' jpeg. :(

I tried simply changing the file extension to .txt. That way the user would simply need to change the file extension back to .xls... i.e. there would be no file conversion really going on, just a file extension swap. However, the second problem is the file size is over the miniscule limit that attachments are allowed. Do you think it would be possible to increase the attachment size that is allocated? I find this not only a problem with trying to attach technical documents, but also the attached pictures are really tiny to the point of not being worth attaching :biggrin:

[Tom @ Fast Forward]

http://www.FastForwardSuperchargers.com/videos/Solo2_Project_Blown_Engine2.wmv

Anywhere we can see this video??? :)

[Tom @ Fast Forward]

Bill,

Try again. I added the excel xls extension as valid and set it to 200K.


I tried simply changing the file extension to .txt. That way the user would simply need to change the file extension back to .xls... i.e. there would be no file conversion really going on, just a file extension swap. However, the second problem is the file size is over the miniscule limit that attachments are allowed. Do you think it would be possible to increase the attachment size that is allocated? I find this not only a problem with trying to attach technical documents, but also the attached pictures are really tiny to the point of not being worth attaching :biggrin:

[FormerDatsun510Man]

Well, my point was really about the problems, or lack there of, for single point of injection. IE. Carburator or Throttle Body Injection. I was trying to infer that it was the best but that the distribution must have been pretty good or a lot of people would have blown engines back in the days of my childhood with big blowers and carburetors. :)

My stock kits with the 5th injector have the 5th injector running at a max of 25% and typical of 12% (halfway). The 5th injector is 480 cc or basically = to two stock injectors. Running at the typical 12% = ~58cc/min. The main injectors are running at about 80% or 0.8 * 240 * 4 = 768. 58/768 = 7.5%

Maybe the Coldside is just more efficient? ;)

Now, if you compare my base 200WHP kit to your 240WHP kit, you need 20% more fuel. As your main injectors are running 10 % less than I do, I can see where you are running the extra injectors a lot.

My second point was that pulsing fuel at the closed intake valves 3 out of 4 pulses (I assume you have the SS set for 4 cylinder 4 cycle?) doesn't do much but possibly puddle the fuel at the closed valves. When the valve finally opens, the fuel is not atomized very well and may require more fuel to make the same 12:1. Remember, the wideband O2 sensor is reading how much air is consumed, not how much fuel. If there is unburned fuel, it will not register as rich. A good example is a misfire. With a misfire, all of the fuel goes into the exhaust pipe but the O2 sensor will read lean, not rich, as the air was not burned either.

Just guess as we really don't know one way or the other. As I said earlier, we have measured the temperature of the four exhaust runners when on the dyno and saw negligable difference from one to the other so the distribution must not be too bad. On my coldside running well over 15PSI on 91 octane in AZ heat, it must not be too bad either or parts would have popped out by now. :)

With respect to A/A intercoolers, that video of the boys at BRP drifting the customers car in the parking lot until the piston exited out the passenger side is one example where I would much rather had E-Cool. A/A ICs don't do much when there is no forward motion. ;)

Again, there is a difference in the design of an intake manifold for a carburetor vs. one for MFI. As I pointed out, the runner length from the point of fuel mixing with the air to the intake ports is kept pretty close on carbureted manifolds. Either with a single carb which is centrally located on the manifold, or with multiple carbs there are individual runners mated to each carb barrel. In contrast, look at the stock Miata intake manifold. Putting an extra injector at the dummy TB is going to have different flow paths and distances to the four cylinders. A few important points though:

1) These comments don't apply to the Coldside which has a plenum style manifold with the extra injector located at the blower outlet. I wouldn't be surprised if this gives very good fuel distribution :)... at least I don't see a problem with it.

2) I don't think the extra injector is a "problem" on Hotside setups running say up to 220rwhp. It is just that I wouldn't chance it above that power level.... at least not without an R4 manifold, which is a plenum design that would probably yield equal fuel distribution with a single extra injector.

3) I don't buy the extra four injectors causing fuel puddling problems. If this were the case I would see a drop in output. On the contrary, my setup is making at least the same rwhp per pulley size as the lower powered setups. If the fuel mixing was less good, or worse, causing misfires, this would cause a loss in rwhp output.

Regarding Air/Air Intercoolers. I don't know why that was brought up in this thread? As far as I have seen to date, they become necessary at a certain point on a Hotside setup. I buy the extra injector concept working because you have proven it on the setups here. But that is ~200rwhp. At 240rwhp, I don't see a choice, and given the fact that I don't do continous burnouts in the parking lot for 5 minutes I don't see it as a problem. I used to have a post IC temp gauge mounted in my car and am very familiar with how the Air/Air IC effected air charge temps. Even stopped, I never saw the temps go more than 50 deg F over ambient. As soon as you would move the car the least bit forward, we're talking like 10mph, the temps would drop immediately.

Bill

[calichtr]

FormerDatsun510Man beat me to the dependence of the IM design on how well it would seem a single injector could work. After all, people like Edelbrock made lots of money selling people better designed IM's for years (and still do) compared to either an OEM Miata which wasn't designed at ALL for an A/F mixture and I don't know if whomever (maybe you?) designed the IM you use with MP-62 coldside had even Air/(especially)Fuel mixture distribution in mind when it was designed or if the 5th injector was a subsequent add-on to get more power out.

And I wasn't trying to infer anything bad about your system for the design point you sell, but rather for people trying to get higher (like 230-240 or so) WHP. Just to be sure, you talked about 15PSI with 91octane... but I assume that is not the normal level in you standard kit for around 200WHP, right?

Cripes, you guys write too fast, by the time I read your posts and try to reply, someone has beaten me to it :hang:

[FormerDatsun510Man]

Thanks Tom! Attached is the fuel and water injection excel spreadsheet. I have the values in it for what I estimate I am running.

Bill

[FormerDatsun510Man]

You know, I probably can prove this with my setup though I was just thinking :). With no change to my engine management I could get a 550cc or so extra injector and put it in the down pipe to the intake manifold, there's a bung already there for it. Then I could simply unplug the four extra injector connectors and connect one of them to the single extra injector. The split second map would have the same curve (probably, hopefully :)) just would need to multiply it by 550/270. I could run it both with the 4 extra injectors in runners vs. single extra injector at the dyno with the same a/f ratios and see if there is any appreciable difference in power output and also if I am having to injector more or less fuel with either setup.

I thought the last dyno was going to be my last LOL. All in the name of progress! :biggrin:

The other test could be no extra injectors and simply 440cc main injectors run by a Megasquirt. Just kidding Tom! :biggrin:

Bill

[Tom @ Fast Forward]

Well, California just confirmed that the stock manifold is different from the Coldside manifold. No CARB on the hotside without a new test. Strictly based on the shape of the manifold. I think you would agree that 'emissions wise' there is no difference. Ah well.

[Satisaii]

Hey Bill,

Do you know what belt size your set-up is using?

I am about to go buy one, and need a starting point for a 130/65 combo.

Thanks,
John

[FormerDatsun510Man]

Yes, I am running the Gates 60439 size belt. It is a tight fit with that belt size. However, I am running a BRP prototype tensioner which I think needs some more work. I would like to run the next size up, which I believe is either a 60441 or 60442.

Bill

[Tom @ Fast Forward]

25-060441 is next.

[Satisaii]

Thanks for the info.

[Tom @ Fast Forward]

Here is a copy of the NAPA page on belts in the range we use.

http://www.FastForwardSuperchargers.com/NAPA-Gates-Belts.jpg

What you might find interesting is that you can buy a 060455 belt for example and have several different lengths? :) The 6PK number is supposed to represent the length in mm and the 0455 number is supposed to mean the length in inches (45.5"). Doesn't make a lot of sense, does it? :) 45.5" = 1155mm. About in the middle of the numbers listed.

[Satisaii]

Major thread hijacking here. What I thought would be a simple question has turned on me...

Where do you go to get these things? I went to the three closest stores, and the only belt that was close (and not special order) was the 6PK1120. I have not REALLY tried HARD to put that one on (it won't go easy), but I think I need one size up.

[Tom @ Fast Forward]

Normally, around here, if NAPA doesn't have it in stock, they have it here in one to two days. You can also take the number to AutoZone and ask for the Gatorback. That is also a great belt and they sometimes have between sizes as well.

[calichtr]

Well, California just confirmed that the stock manifold is different from the Coldside manifold. No CARB on the hotside without a new test. Strictly based on the shape of the manifold. I think you would agree that 'emissions wise' there is no difference. Ah well.

Huh? Humor/sarcasm? Sorry I don't know more about your parts... any chance of you posting more pix on your main (non-forum) website of your pieces?

[Tom @ Fast Forward]

Sadly it was neither humor or sarcasm. They actually said that the main reason for denial was that the stock intake manifold was different from the one I used for CARB testing on my Coldside. I then wrote back and offered to use my Coldside manifold on the hotside kit and was then informed that the crossover pipe could really mess up emissions and that would require re-testing even with the same manifold.

I find it unbelievable but there it is.

[wineguy]

...I find it unbelievable but there it is.

Believe it, unfortunately. It's hard to imagine how a stock crossover tube carrying nothing but slightly compressed air is going to mangle the tailpipe emissions! Of course, only in Kalifornya...

WARNING -- THREAD DRIFT/RANT FOLLOWS:
That's alright, I had the TTB (federal agency replacing the ATF) deny a permit application because the filed dba said "XYZ Co.", and the permit application said "XYZ Company". Consequently, I re-filed another dba with the correct semantics -- it is my opinion, that there are two many governement agencies that are relying less on the law and it's intent, and more on "inter-office policies" regarding stuff like this.
[thread drift=OFF]

Thanks :rolleyes:

Anyway, keep up the good work, Tom!