need info

Fifth Generation Honda Prelude topics

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ladieslovecoolludes
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need info

Post by ladieslovecoolludes »

hey people i recently started an n/a rebuild plan is as follows: -full port and polish head (intake and exhaust ports and combustion chamber), whole intake and throttle body -head planed -block decked -oem gaskets -throttle body spacer -440cc injectors (talon or bosh) -255 walbro in tank pump -aem fuel rail with adjustable regulator -stock cams and valvetrain -h23 pistons & rods -header 4-2-1 (not sure which brand yet) -high flow universal cat (probably magnaflow) -2.5" pipes with most likely 3" muffler. So i need to know if i need to have a different control unit (or can i just have some kind of piggyback system) and what is a safe pressure i can run to get max power but not to burn everything up. I also heard about deleting iab's for more top end with slight unnoticable bottom end loss---true or myth?

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spiffyguido
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Re: need info

Post by spiffyguido »

Not sure about the intake air bypass. I've read arguments both ways.

When you say 'Safe Pressure', I assume you're are asking about a compression ratio as this is an N/A build. Please clarify. Compression ratio on an N/A build will depend a lot on the type of fuel you plan to run and where you live.

You likely won't need a new control unit as long as you've picked the injectors correctly. If the injectors require a difference pulse width than what your ECU is putting out, you will need to make some modifications. AEM makes excellent plug and play engine management systems that allow for a lot of customization.

You'll want to double check which AEM model you need, but here is one that might be the correct one:

AEM 30-6060 Series 2 Plug and Play EMS
Note: As an amazon associate, I earn from qualifying purchases.

The AEM engine management systems are very powerful. I've used one before on a Formula SAE car and the freedom they provide can be very useful if you know what you're doing. Keep in mind though, the learning curve is steep on such a system and you can completely destroy your engine if you get something wrong.

ladieslovecoolludes
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Posts: 9
Joined: Tue Feb 28, 2012 7:17 pm
Location: quebec, canada

Re: need info

Post by ladieslovecoolludes »

thanks for reply. as for pressure i meant what is the highest fuel pressure i can dial in (or should i just let the factory control unit take care of it via sensors.

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spiffyguido
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Re: need info

Post by spiffyguido »

Use the fuel pressure regulator to get the pressure that you need. Running a higher pressure should be just fine, although, since you have enlarged injectors, I can't imagine that you would need to raise the pressure much. Your engine will be getting plenty of fuel. Just make sure you're running an optimal air-fuel ratio for your altitude.

ladieslovecoolludes
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Re: need info

Post by ladieslovecoolludes »

Cool, thanks:-) ... Do you have a formula for optimal fuel air ratio and how would i go about adjusting that?

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spiffyguido
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Re: need info

Post by spiffyguido »

Before you start worrying about the altitude, you need to get the pressure question sorted out. Your stock injectors will have had a flow rate at a particular pressure. At your new pressure and injector size, you'll have a new flow rate. Once you know the new flow rate, you'll be able to see how much fuel you're going to be getting. At that point, if your flow rate is much higher you need to worry about adjusting things lest your engine won't be running in an optimal range. If the injectors just make things a little bit richer, you won't need any further modifications because your sensors will adjust for altitude SLIGHTLY on their own.

The point I was trying to make was that you need to make sure that you aren't running too rich with your enlarged injectors and potentially adjusted fuel pressure. Altitude plays into this because at different elevations the optimal air fuel ratio changes because the ambient air density changes. Start by figuring out what your air fuel ratio has become, then you can check whether you should be concerned based on where you live.

Good reading here:

http://en.wikipedia.org/wiki/Air_Fuel_Ratio

I also have some formulas for calculating the injector flow rates. These are easily found on the internet with a Google search, but if you can't find one, let me know and I can look them up in my book.

ladieslovecoolludes
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Joined: Tue Feb 28, 2012 7:17 pm
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Re: need info

Post by ladieslovecoolludes »

hey i did some lookin around and all i could find was a bunch of equations and in which the variables were maf, map, pulsewidth. i looked through my manual and it just gave me the old fuel pressure with the factory fuel pressure regulator unhooked and pinched (47-53). but i can t make heads or tails of the rest of it. i understand well about fuel air ratios and efficency and am pretty mechanically inclined but the other stuff is makin my head spin!! lmao :lol: help please

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spiffyguido
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Re: need info

Post by spiffyguido »

Assuming that you have an H22A4 engine, the injector size should be 290cc. The injectors are type saturated.

With your new 440cc injectors (which should also be saturated type) your fuel flow will likely have increased by about 50%. With injectors that big, you're certainly not going to need to increase your fuel pressure. You're already going to be getting a ton of fuel. 20% increase is generally considered to be the limit of what the engine can just cope with on its own. You're beyond that, so you'll need to assess other variables.

To know the actual flow rate of your new injectors, we need to know what pressure the 440cc are rated at. Then, with that information in hand, you can calculate what your new flow rate is.

For an example, let's say that your new injectors are 440cc at 40psi. Using the formula (and convenient calculator) at http://www.rceng.com/technical.aspx you can make the following calculation to see what your new flow rate is. In this case, you have to assume that your current injectors of size 290cc were rated at 50psi.

Plugging in the numbers, we see that your new flow rate is 491.93 cc/min. That's a lot more.

If you want to figure out what this means in air/fuel ratio, you have to do some much fancier math. A basic example of the formula is as follows:

AFR = Mass Air Flow / (Injector Pulse Width * 4 injectors * (RPM/2) * Injector flow rate)

RPM is divided by two because the injectors obviously only fire once per every two revolutions.

In practice, this isn't going to be easy for you to figure out, because you don't know what the injector pulsewidth is for your car. If you got a custom ECU, you would, but with your stock setup, there's no way to determine this.

When sizing injectors, most people actually rely on a much simpler formula. The ECU meddles with the air fuel ratio a lot, so unless you're getting a custom ECU, just let the stock ECU take care of mixing fuel for you and instead make sure that your injectors are large enough to get the power that you think your engine should be pushing out.

For the formula, go to http://www.rceng.com/technical.aspx and look under "selecting the proper injector size". This formula has been in every performance tuning book I've ever read. It's simple, and it works.

Since you're going N/A, your values are probably like the following:

HP = 230
BSFC = 0.5 (always 0.5 for N/A)
Max Duty Cycle = 0.8 (again, this is always the estimated max of an injector)
Fuel Pressure = 50psi (unless you change it)

This gives you a suggested injector size of 352cc/min. If you haven't already purchased your larger injectors, you might want to consider getting some of this size (make sure you get Saturated injectors) unless your H22 is from an older Prelude.

For your information, the formula for comparing fuel pressures and AFR values goes as follows:

New fuel pressure = stock fuel pressure * ((old AFR / new AFR)^2) + 1

ladieslovecoolludes
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Joined: Tue Feb 28, 2012 7:17 pm
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Re: need info

Post by ladieslovecoolludes »

sweet! i thank you very much for the help, it s appreciated. i ll keep you posted as i make progress. Cheers!



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