I built and swapped a K24A1 into my EP3 a couple years ago, below is the setup. I chose this set up to create strong low-end power for track days and auto-x, and was hoping to maintain some good top end to reach the 350-400whp mark. I was not expecting to be limited on power the way I was told I was by the tuner.

I got it tuned by someone in Socal who I'll leave nameless for now. The motor made roughly 275hp/275 ft/lbs, (see attached graph) at about 12-13psi and the tuner said the engine in it's current set up won't make anything more. Although the 650 injectors were working at 85% duty, he said even if we extended that, it won't help.

He blamed it on 3 things:
1. K24A1 head was too restricting and non-vtec wasn't helping. However, everything I was told at the time was that it was one of the highest flowing K heads.
2. Log manifold- said I needed a side winder, that there's no way to reach 350-400 on a log manifold. We have all seen motors with log manifolds make 500-600hp, so have to call BS there.
3. Octane- this is all on CA 91 octane. He said if I convert to E85 I can hit 350 no problem. Although this may be true, I don't see why it can't on 91.

Is this in with what you guys think? Where am I truly limited? and what's really needed to hit that 350-400 mark?

K24A1 Block and Head (non-vtec head)
Arias 8.8:1 pistons
Eagle Rods
Precision 5731 t3/t4
Stainless Log top mount manifold
3" downpipe
650 injectors, stock fuel rail and pump
Kpro- early version- got in 2006

 

On an engine with static compression that low, you should not be knock limited by 91 at only 275whp. I would think 400whp range should be obtainable on that setup.

Get some bigger injectors, take it to a different tuner and have them throw some more boost at it.

 

^^ Solid gold!

 

What size injectors are needed for 400hp? If I'm maxing 650s at 275

Also, does a bigger/higher capacity fuel pump reduce the duty on the injector? What is the hp capacity on a stock fuel pump?

 

Get rid of that fuel pump and get a 450 walbro. I'm running the 525 Hellcat with 750cc injectors at **approximately** 400whp pushing only 58% injector duty cycle.

 

The way you decrease duty cycle is increasing fuel pressure not necessarily pump size as that is a measure of flow.

A walbro 255 is more then enough for your goals you can go higher on the pump but not necesarry.

The only limiting factor I see is the pump

really such thing as too restrictive of a head at this power level just throw more boost at it and turbo should be capable.

Did tuner say what duty cycle your injector is at?

 

Need bigger injectors IMO , I use the DW 400 in-tank pump and it’s spot on. My walbro 250 ran out around 300whp. That’s a very low compression, I’ve never seen how these motors responded with that low compression before myself

 

A walbro 255 will make way more then 300 heck op made 265 on a stock pump. Do a quick search most 255s max at in-between 500-600 perhaps you had a bad or fake walbro.

I made 430 on mine no fueling issues... B18c 1000cc walbro 255

https://honda-tech.com/forums/forced...-flow-2374631/

 

Walbro states 500hp limit on the 255, and 750hp on the 450.

I'm sure the 255 will be fine. Tuner said I was around 85-90% on the 650s. How do you increase fuel pressure? (lower duty on injectors)

I think I can go to 750s plug and play, but going bigger requires further modification, fuel rail, etc, right?


8.8:1 compression is the lowest I've seen someone do with a honda as well, but I took a chance. I'm happy with it, it responds very quickly and I enjoy the power curve, I just want more.

 

you increase fuel pressure with a fuel presure regulator, it does not necessarily require a fuel rail. if you upgrade fuel pump you need a fpr otherwise the stock FPR will not deal with the increased flow properly.

larger injectors dont require anything unless you go from low impedence to high impedence just a retune

 

Thanks for the fuel system info.

Going back to the original post, could I actually be knock limited at 275hp?

 

‘I’m on corn which takes about 30-35% more fuel, that why I’m sure. Either way I made sure I had plenty of fuel with the DW 400 and 2200cc injectors. I’m hitting a max duty of around 69% on the injectors @ 29psi

 

well theirs the difference ethanol takes ALOT more fuel. OP is on pump gas.

the 255 is not a ethanol friendly pump either so its good you swapped it out

 

Remember that the OP has an EP3 chassis. The stock fuel system is a return-less system... which is far less efficient than the older return style system. The regulator is mounted inside the tank. There is no boost reference connected, so fuel pressure does not raise under boost.

Not really possible with the stock fuel system... the OP would have to convert to a return style fuel system to get the benefits that you have discussed.

Unlikely... but you are injector limited.

 

What is the benefit of a return style line?

So I definitely need bigger injectors, but what size? Can I get away with low impedance 750s, 1000s?

I still may also be fuel pump limited. If I drop in a 255, do I need to do anything else?


Would uploading a kal and datalog here be of any use in figuring out why the tuner said I was knock limited?

 

Brother get a k20a2 or k20z1 head. It will be day and night difference.
Also check if by any chance you have a .48 a/r turbine housing.
If its an octane problem get a simple water meth kit and youll be able to hit another 100whp easy.
Do you have a picture of the turbo manifold?

 

Possibly knock limited due to the way the stock returnless system works. If your stock fuel pressure regulator has no boost reference hooked up and does not add any fuel with boost, you're a ticking time bomb. Just my thought anyhow..

 

Did some reading. Sounds like I need a new fuel pump, FPR and return line to create the fuel pressure necessary for boost. And this correctly regulated fuel pressure can reduce the knock risk? And I getting this right?

And it will also reduce the duty on the injectors.

Anyone have any socal tuners they'd recommend?

 

Without having a return it’s pointless to have a boosted setup. Why have a built motor and not 3-400 invested in a regulator and line? I don’t get it.

 

A good adjustable fuel pressure regulator should provide 1:1 rising rate fuel pressure. This gives you an additional psi of fuel per psi of manifold pressure; more fuel for more boost. If you're unable to get enough fuel, you run the higher risks of detonation. There are others here that can better answer that question, or at least explain it better. You may be able to get away with just larger injectors but, I'm not overly familiar with a returnless system.

 

I must have skipped over the stock fuel pump and returnless system when I initially read this post. That is a big bottleneck for the K series platforms.

You definitely need to switch to a return style system and upgrade your fuel pump.

 

Thanks for the info everyone. I was completely unfamiliar with fuel systems in general, but this makes sense. I'll be putting together a return line system.

Can I do a fuel pump, FPR, return line by itself or do I need an external fuel filter and fuel rail as well?

Love how active h-t still is after so many other forums have died.

 

Forget the Walbro 255... go straight to a Deatschwerks 300C and you will be good. I would NOT recommend low-impedance fuel injectors... K series ECU's are too dang expensive to replace when you burn the injector drivers out. Get a set of 1000's for conventional fuel or a set of 1200's if you intend to run the car on corn.

You can convert to a return style system... but this will require a pump, pump hanger system, braided fuel lines from front to rear, an external fuel filter, a FPR, an aftermarket fuel rail (with an inlet AND outlet)... and then you will still need a set of 750's for pump gas.