How to Make 396 Hp at the wheels

[4g62bt2c30a]

hejo,

I think you are right on in your previous post. The math is as close as I think you can get. The reason I did not want to respond directly because I hoped that someone would take your knoledge and due some due diligence that I would not have to do. My point is this, I may be wrong but it just looks like it took a lot of work to make it all work. at 98% duty and 96 psi it seems like you are pushing the dead limits of all the parts involved. The information on this is out there you just have to look for it.. What happens to injectors at 98% duty? What is the effect of 96 psi over any kind of extended time? I am limited to what I can say due to my past posts..( That was my own doing)... I think that there is little room for error in your math and in the hardware used. It is gonna work or not... How do things such as air temp and altitude change these #s? If you have the ability to alter the fuel curve with a computer wouldn't it better to go with a larger delvery system and then tune with the black box? Big fuel pumps are cheap and you can always use injectors out of another vehicle to cut costs...


Corey

 

[hejo]

Corey I think your points are well founded. However this is why Mark is doing the testing that he is.... I hope people understand what it means to have you're car be a test platform. As he stated and I beleive he's an honest guy, he'll do the right thing to make a reliable product based on testing.

So I think where things got off track when it was being stated that it wasn't possible. Well it is possible as he's proven but the question you and a few others are asking is but how reliable. That's a very valid question to ask. I don't think Mark has the questions for that yet but it does seem to me he's doing some pretty heavy testing. Yes temp and alltitude are going to have an impact.

 

[4g62bt2c30a]

Originally posted by hejo:
Corey I think your points are well founded. However this is why Mark is doing the testing that he is.... I hope people understand what it means to have you're car be a test platform. As he stated and I beleive he's an honest guy, he'll do the right thing to make a reliable product based on testing.

So I think where things got off track when it was being stated that it wasn't possible. Well it is possible as he's proven but the question you and a few others are asking is but how reliable. That's a very valid question to ask. I don't think Mark has the questions for that yet but it does seem to me he's doing some pretty heavy testing. Yes temp and alltitude are going to have an impact.

Thanks for you response....
Corey

 

[cobalt]

Originally posted by JChoice:
DanO: Have you considered RC engineering? As far as I knew, they were the "Go to" guys for this type of stuff.

Yes, RC Engineering does clean and blueprint injectors. I would think that with a boosted NSX, you should be using a 320cc injector...

 

[DanO]

Originally posted by hejo:
Anybody got answers to DanO's post?

Well, I’m working on the answers…

Question 1 (pressure in the manifold in relation to fuel pressure)
This evening I had a chance to have a brief discussion with an engineer who’s worked in the Detroit auto industry for over 30 years and he answered my first question about manifold pressure and how it relates to our psi measurements. Basically he said that the pressure across the injector in the manifold is what counts. To maintain a constant differential fuel pressure in the manifold, cars typically use one of two ways: 1) they use a manifold absolute pressure (MAP) sensor and a fuel pressure regulator to lower the fuel pressure under vacuum and increase it under boost, or they use the MAP sensor/ecu to adjust the cycling of the injectors. It appears that our NSX uses a fuel regulator attached directly to a vacuum hose off the manifold and varies the fuel pressure from around 40psi to 50psi to maintain a constant 50psi in the manifold. It is a 1 to 1 relationship, that is, if the manifold is at 5psi and the fuel rail is at 50 psi then the real pressure across the fuel injectors in the manifold is 45psi.

Next I started picking his brains about the “Duty Cycle” of fuel injectors and how much time is there to inject fuel because this whole thing is rather fuzzy to me. Unfortunately, we ran out of time well before we ran out of beer and graph paper so we didn’t get too far, but he did start to clear some things up: Obviously, the duty cycle of an injector is the ratio of time an injector is “on” compared to off. But the definition of “on” is not necessarily what I assumed it to be, which is 1 / RPM x 2. I guess it’s somewhat less and therefore 100% duty cycle does not equal static flow rate…anyway we ran out of time but I’ll pick back up on it next time I see him.

Question 2 (NSX fuel pump relief valve)
I have not heard anything back from anyone regarding this question. I guess I’ll just have to buy a fuel pressure gauge, plug the line before the regulator and crank on the fuel pump until the pressure stabilizes (or blows out a line <g>) and see what this relief valve is all about. Anyone want to volunteer for this or am I going to have to do it myself? <g>

Question 3 (injector blueprinting company)
I talked to RC engineering today (thank for the advice guys!) and the guy I talked to was real nice and informative. I’m going to send in my injectors (why not as my fuel pump will be broken <g> (see above)) to have them cleaned and then flow tested at various levels up to 100psi. The gentleman indicated that the NSX injectors were very high quality and I should expect them to flow at 240cc at 43.5psi and to follow the “formula” as the psi increased.

I think this will be my last post on this thread because I think it’s gotten technical enough in nature to move to the tech forum and is quite a bit off topic. If hejo wants to repost his equations and numbers as a topic on the tech list I think that would be really cool place to continue this discussion.

BTW, I am not trying to prove or disprove anybody’s hp gain claim or make any claims about anybody’s upcoming supercharger product <g>. Nor am I trying to second-guess Mark B’s beta fuel management system as Mark has forgotten more about cars then I’ll hope to ever learn; my interest is purely educational.

DanO

 

[sjs]

Thanks DanO!

I wouldn't be too concerned about testing your pump. Before replacing mine I "dead-headed" it numerous times to measure it's max psi at idle and under load. (Mine never go high enough for this test.) To hit the desired levels you will probably need to bypass the resistor. It's the small finned block just above the fuel filter. Pull the connector and stick a jumper wire across the two sides. That will allow 14+ volts to the pump.

 

[BryanZublin]

DanO wrote:

> 1) they use a manifold absolute pressure (MAP) sensor and
> a fuel pressure regulator to lower the fuel pressure under
> vacuum and increase it under boost, or they use the MAP
> sensor/ecu to adjust the cycling of the injectors.

I think you will find that 99% of the cars (including the NSX) use a mechanical pressure regulator referenced to the manifold pressure so that the pressure across the injector is maintained at a constant value. A MAP sensor does not play a part in this method.

>It appears that our NSX uses a fuel regulator attached
>directly to a vacuum hose off the manifold and varies the
>fuel pressure from around 40psi to 50psi to maintain a
>constant 50psi in the manifold.

Yes, I think 50 psi is what is listed in the repair manual.

>It is a 1 to 1 relationship, that is, if the manifold is
>at 5psi and the fuel rail is at 50 psi then the real
>pressure across the fuel injectors in the manifold is 45psi.

Yes, this is correct. However, with the NSX pressure regulator, if the manifold *was* at 5 psi (only possible with forced induction), then the regulator would actually increase the fuel rail pressure to 55 psi to maintain 50 psi across the injector. I haven't tested the stock NSX pressure regulator to see if it is still linear with boost, but I would guess that it will still work for moderate levels (5 to 10 psi).

Regarding the injector duty cycle, it is calculated / measured as follows:

DC = 100 * ( Ton / (Ton + Toff) )

DC: Duty cycle (%)
Ton = time duration that the injector is ON, for one injector cycle
Toff = time duration that the injector is OFF, for one injector cycle

A 100% duty cycle represents an injector that is ON all the time (Toff = 0).

The term (Ton + Toff) is equal to the period of the injector cycle and is related to engine speed (RPM). More details can be found in any EFI book and can probably be better explained than my attempt.

By the way, many people quote the 80% max duty cycle as a desired limit for injectors. The fact is, unless you have added an external circuit to change the duty cycle, or have modified the ECU, the max duty cycle that the injectors see is based on what Honda has programmed into the ECU. Under wide open throttle and high RPM, maybe it's 70%, maybe it's 90%, we don't know unless it has been measured.

>I’m going to send in my injectors (why not as my fuel pump
>will be broken (see above)) to have them cleaned and then
>flow tested at various levels up to 100psi.

Please post the data when you receive it. I have not seen this data on the web.

Regards,
Bryan Zublin

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Zublin Engineering
http://www.zublin.com