I am upgrading my fuel system, and I want to be able to eventually support 800hp (at the crank) on E85. Raceworks' calculator shows I'll need 410lph (108gph) at 57.5psi, assuming 14psi of boost. I know this is going to require some combination of a big pump(s), upgraded wiring, and upgraded fuel lines.

Pump: A Walbro 255 is good for 58gph at 13.5v and 60psi. Even with no pressure drop over the 3/8" lines, two wouldn't cut it. The Walbro 450 does 75gph at 13.5v/60psi, so maybe one of each? What do you guys suggest? I hear big pumps can be pretty loud, so I'd prefer to have two and run the second only as-needed.

Wiring: I'm planning to run new wire from the battery with one relay connected to the old power feed and another connected to my standalone. The Walbro 450 alone pulls 20A, so I think I'd need 6AWG or two runs of 8AWG. Also, I understand the oil pressure switch supplies fuel pump power in parallel - do I need to touch that circuit? I've heard alternate explanations that it's a "backup" power supply and that it is a safety measure that cuts fuel if oil pressure drops.

Fuel lines: If '85 and up Corvettes have E85-safe fuel components as I've read, I don't *technically* have to touch the fuel lines. I have no experience running fuel line, so I don't want to do this if I don't have to. People say the stock 3/8" lines can support 1000hp on gas, but the question is whether it's worth buying bigger pumps to make this happen.

Other: Fuel rail? FPR? (Obviously injectors.)

 

Ive asked the same question.

hopefully you’ll get useful answers instead of smart-alec ones.

the c4 tech forum died a long time ago. A lot of the people that made their c4 beat/compete newer stuff are long gone. Mostly whats left is clowns on here today. Dont expect serious answers in return.

That said, I tell you what I know.

Injectors: you are going to need at least 80’s.
i was running > 100% DC on 60’s above 6000 RPM with E 50 (a blend of e85 and 93 to achieve 50% ethanol)

since im using the stock batch fire 1993 computer I dont want to go over 80’s bc i worry about idle quality.

Fuel Pump:
No issue with my 450 l/hr pump being loud. I also have removed the unusual fuel pulse dampener.

most of the c5 forced induction guys running 700+ rwhp e85 run 2 walbro 450 l/hrs. They use a Y inside the fuel tank sender and have the second pump come on with boost above a certain level. Hobbs switch style. I believe it connects the ‘ground’ for the second pump once the trigger (ie. Boost point, or nitrous solenoid activated) is reached.

running both pumps full time just heats the fuel and uses a lot of amps.

I plan to run a second 4 pin bulkhead connector(for fuel pump 2) to ensure the existing bulkhead power plug connector doesnt become overwhelmed with the current from both.

obviously you want a racetronix hotwire style harness (due to the heavy gauge wiring). I plan to use that to feed BOTH pumps power.

when i first put in the 450 l/hr pump it fried the OEM 3 pin bulkhead connector for the power resulting in a no start condition. Racetronix sells a 4 pin bulkhead connector that you MUST use.

the in tank wiring MUST be upgraded. I have a list of racetronix p/n’s to do this.

im going to put a fuel feed bulkhead pass thru, for my fuel feed, that mates to the Y inside the fuel pump. It will have a 90 degree outlet (on the top side of the sending u unit) and mate to -8an fuel feed line.

fuel line: I plan on using a -8AN line as my feed to another Y that distributes fuel to the firewall ends of each rail.

fuel return: There will be 90 degree elbow fittings with -6an coming off the front sides of each rail. they will go into yet another Y and go to a fuel pressure regulTor and then back to the tank.
i may try to use the current fuel feed line as a return, or else put a -6AN line in as the return back to the tank . That way I wont have to add another fitting to the sender. Obviously i will extend the return line (formerly feed line) down to the bottom of the bucket with that hard plastic corrugated ‘straw’ like tubing.

fuel rails: convert to parallel feed (and return). Google it. Lt1 parallel feed fuel lines.

fuel pressure regulator: obviously need an aftermarket one. Ive heard some of the adjustable ones are junk (ie. Dont hold pressure steady) . Though thats ancedotal and i couldnt tell you which ones are bad.
if someone here has a recommendation....

good luck, im doing the same thing on my 1993

 

Your butt hurt is showing Diz. You've done all that and you still run 12's.

 

On the 84, my oil pressure switch is in parallel. So if the car were to shut off but maintain oil pressure as it does for a few seconds... the fuel pump continues to run. It is not a safety in that if you lose oil pressure it will kill the fuel pump. At least how it us set up on mine. You can wire it that way.

I checked and ran some numbers and I come reasonably close... I am figuring 120 GPH realistically... this gives you pretty safe headroom and assumes a **** poor BSFC on E... may not be a bad idea to reach out to TI automotive... I was told by walbro they manufacture their pumps and provide all the data and tech sheets too. You can do it on 3/8... you just need pumps with high working pressure hence the pump curve. You're looking at roughly 14 psi of head on the pump on top of what you set your regulator to. So you're looking for a pump that can flow that at 72 psi since you are setting to 58... I'm a bit rusty though and it gets easier as you go up in tubing size but it can be done with 3/8 no problem...

 

seriously dude.

after years of being helpful, its like you just graduated 7th grade recently.

Im not sure why you are he11 bent on insulting on me.
ive always had nice things to say about your race only c4 setup.

 

I wouldn't worry too much about it Diz.

Back to the topic.

I run a 340lph pump to support over 700fwhp BUT, and it as a rather large caveat, I am on a different flow curve. Base pressure around 8psig and a peak of around 24psig. At that peak pressure the pump is still capable of flowing nearly 370lph per the manufacturer. The current draw is low at that pressure, so its done through the factory wiring/bulkhead.

My tank is delaminated and the sender is mostly rust, so I plan to rip it all out soon and replace it with a fuel cell. When I do, I'll likely add a 2nd AEM 50-1000 pump for the new engine that will require more fuel.

410lph for 800hp sounds low for a high pressure forced induction application. IMO

 

There is a simple answer to this. First off, calling people here "clowns" does not help your cause. Secondly, if people are giving you "smart-alec answers", you have brought that on yourself. Right or wrong, people will react that way after years of your non stop ridiculous threads. Every time I see a weird thread title pop up, I don't even have to look to see who posted it. If you see C4 Tech as not being worthwhile anymore, you have contributed to making it that way. Do you not think that posting **** like "Will the optispark still work with an LS(paraphrasing) damages your credibility? Go to your own profile and look up "Find all threads started by Dizwiz24".

Everything takes time. Stop with the nutty threads and after awhile people will see maybe you are serious and will truly help out. Stopping the butt hurt you have shown here will go a long ways also. We have heard ad nauseum about how you "dreamed as a kid about owning a C4". Well, supposedly you are a grown man now so stop the "dreaming" like a 14 year old girl clutching a poster of Justin Beiber.

 

arbee,
I feel a lot of people here have ‘given up’ on the c4 platform.

dont mistake my comments (about using an optispark in an ls swap) as a joke. Most are serious inquiries.

I would like to create a c4 tech sub forum with ‘serious posters only’. Those people who are still actively mod’ding vs. those who havent improved their
setup in years and just come to ridicule those that are still serious about the c4 platform.

I come to the c4 site with passion about the platform and get made fun of by those who have given up on it

 

Thank you all for your help! Less so for the both passive and direct aggressiveness though.

You know, I was thinking 80s but that was with a previous power number in mind. Assuming a high BSFC of 0.95 for a supercharged E85 engine, 800*0.95/8 = 95 lb/hr per injector. Yikes. I see a single set that would work (EV1, 2.27" seat to seat), but that seems like it would be a nightmare to get to idle, especially on gas. I've kind of toyed with the idea of running a staged setup with an injector or two in the throttle body - has anyone here done that? I know you can run into distribution problems putting wet flow through an intake designed for dry flow, but it would be cool to give the fuel more time to vaporize like a carb.

Thanks for the FP info. I've heard the 450 is quieter than the 255 because it's a rotary style pump. I think I'd trigger my second pump from the ECM based on injector duty cycle, but a backup Hobbs switch in parallel would be a good idea.
Thanks for the info on wiring. I might be hitting you up for those part numbers at some point.

How involved of a job is it to replace the factory fuel lines? And how much do you think doing so will cost you?
I need my engine to pass a visual, so replacing fuel lines/FPR could get dicey. I've heard of people failing smog because of an AFPR. Any stealth options?

Thanks. I just want to make sure there's no scenario where the main pump feed dies, but the OP switch keeps them running at lower voltage and causes a lean condition. If I'm that paranoid I could just program my ECU to kill the engine if it goes lean, though.
That backpressure number is super helpful - how'd you figure that out? Do you have the loss coefficient for the whole system? Walbro's store has the pump curve for the 450, and it looks like at 72 psi it's still good for a little over 90 gph. I'm confused where I got that 75 gph number.

Thanks. Do you run the wire direct to the alternator itself, or just to the nearest junction block? External would probably be easier, but I'd like to quiet it down by keeping it in the tank if I can.

 

The pressure drop is just a basic fluid flow equation. Makes a lot of assumptions but should be in the ball park. Roughness of the 3/8 steel line, 22 feet, 130 gpm etc.. generally when I've tested it gives values on the high end... I based the numbers on the properties of water because I didn't feel like looking. E85 has lower density and viscosity so it may be a psi less or so. Figure at worst 20... and then you'll definitely be safe. As most of my professors have told me... its a guessing game. These will put you in the ball park on a system you know. Until it's tested you never know. It is also a squared increase after a certain point... 65 gpm comes out to 4 something etc. Bigger pipe the less you have to deal with it. But half inch is large... but you have almost no pressure drop to worry about at those flow rates... do you can have a pump that needs to deal with lesser pressure.... really depends. If you can make 3/8 work easily why mess with all new plumbing right?

 

I'm actually working on a degree in fluid mechanics - I just didn't think anyone would want to go through the effort of that calculation, ha. I've done some iterative pump curve calculations by hand and really didn't feel like doing a repeat. I suppose for a conservative number the iteration shouldn't be necessary, as the pressure drop you first calculate -> reduced flow -> reduced pressure drop. It's just like the saying - "all models are wrong, but some are useful."

And 100% agreed on avoiding plumbing if possible!

 

Heres the fuel pressure with me getting on it at just under 12 psi boost (as seen).

Before gunning it, i was seeing 43.5 psi fuel pressure at highway driving (under vacuum).

after I achieve about 12 psi of boost, fuel pressure goes up, but Im just under 50 psi fuel pressure. I would expect to see 55+ psi fuel pressure.

and this is with 93 octane, not an e85 or blend of it.


If I do the same test at idle, using a mity-vac to generate 12 psi boost on the fuel pressure regulator, ill see 55-56 psi.

fuel system stats at time of this experiment:
-450 l/hr in tank pump with all wiring to it (including bulkhead connector and in tank wiring, upgraded).
-60 lb/hr injectors
-new fuel filter

what does this photo mean 🤷🏻‍♂️?

 

Yeah you can go through all the iterations but if you have the curve plus losses... I agree, close enough lol. I've never had a situation where I needed to be that close. Mostly cooling systems where more ends up being better.

 

At 65psi backpressure, a 450 moves 80-95gph. That's ~450 lb/hr, so eight 60lb injectors could very well be maxing it out.


I realized the injectors I linked are low impedance, and Megasquirt can't run those without additional hardware. I'm not finding any high-impedance injectors with that much flow and a 2.27" seat height. What big injectors are people running here? Is there a way to make a different seat height work?

 

Deka 80s will do 800 at the crank on E85 (they'll do 800 at the wheels with enough fuel pressure), and they're fairly cheap.
Decapped stock LS injectors are even cheaper and can do those numbers. Some of them flow over 100 lb/hr.
I'd stray away from Low-Imp stuff. They were relevant back when there wasn't much more available with big flow numbers. That's not the case anymore.

Avoid a single 450. Either go with a Single 525 (which is still pushing it), one of aeromotives brushless in-tank setups, or dual pumps.
450s are bigger than your typical 255/340 at the base because they are technically a different style of pump.
A pair of 340s will fit far easier than a pair of 450s and get what you need.
External pumps are preferable, but noisy.

An aftermarket regulator can solve a few problems, like running lower base pressure and having it increase with boost.
Or running a higher base pressure if you have enough pump, to make your injectors go further.

 

whats your take on the fuel rails.
Should they be modified (ex. Converted to parallel flow)?

or should one just put 2 pumps in the tank, and possibly a bigger line to the rail, keep an eye of the fuel pressure gage during WOT runs (which is measuring fuel press from the middle of the passenger side fuel rail) and see that it doesnt drop in pressure with increase rpm ?

this would be E85, 800 crank HP, 14 psi boost

 

Thanks for the advice.
Funny, I just came across a quite old post mentioning that Dekas worked in TPI. Are they good injectors? I don't want to have trouble idling, and I don't want a big mismatch in fuel flow from cylinder to cylinder with this kind of power on boost.

I was hoping to avoid the 255/340 style because I hear they're noisy. I'll have to see if people have been able to fit two 450s in the C4's tank, didn't realize they were larger. A 525 flows ~105gph at 13.5v and 65psi, which even at an optimistic 0.85 bsfc isn't enough. I guess I could run that with an external booster; if I'm at WOT the noise of an external fuel pump probably wouldn't be significant. That would allow an easy upgrade down the road if desired as well. I can't find a pump curve for the Aeromotive 450, but I imagine it's similar to Walbro 450.

What are the benefits of external pumps other than ease of access?

I wonder if it would be worth it to run Procharger's FMU (adjustable x:1 boost-referenced FPR) to make idle a little easier while still being able to flow at peak. I'd rather avoid that since it doesn't look like there's a way to feed that info into Megasquirt, which means stuff like accel and decel enrichment would be inconsistent based on boost.

Good question. I think I'm going to have to just squeeze all my fuel through the stock rails to pass visual, so hopefully that's realistically possible. I'm planning to run a cheap FP sensor ($20 for the sensor, $13 for a , and then of course some change for a pigtail and some wire to the Megasquirt) to monitor FP and/or cut fuel if it drops too low.

 

Dont mess around with the FMU. Thats outdated stuff people did before they knew the workaroundz to tune the ECM. Today, people put big injectors in , a big enough fuel supply (subject of this post) , drop a 2 bar MAP sensor ipo of the 1 bar into the stock ECM. Thats what im doing on my $da2 batch fire stock 1993 ECM. Tunercat/ Datacat mAkes software to program the ECM and analyze datalogs based on the stock 1993 ecm but using a 2 bar MAP.

since my 1993 is batch fire, im worried about idle quality with big injectors. Its pretty decent idle still on 93 octane even with 60 lb/hr injectors and 224/236 114 lsa cam

My 80 lb/hr injectors arrived and Im going to throw those in, set the injector constant to a higher flow rate, and see if it still idles good on 93 octane. i will be doing that within the next week.

fuel rAils:
Im in a similar situation. I really dont want to mod these if I dont have to. I wish someone made aftermarket lt1 fuel rails like they do everything else for newer motors. However i havent found any.

my issue with modding these to parallel flow is the return fittings off the FRONT of the rail. You have to use some kind of 90 degree elbow off the TOP. It looks bad, and i feel its a fire risk if you put the nose of the corvette under something /broke off those fittings coming off the top. But I guess a meteor could hit you too. 🤷🏻‍♂️

I had a spare 1992-1993 fuel rail I took apart and took this photo.

its interesting there appears to be a ‘baffle /redirect tube’ inside the rail, with its inlet hole partially inline with the Y feed tube line. I show this in the photo. You can see it inside the rearmost inlet hole in the photo.

These tubes end right before the forward most injector.
To me it seems the purpose of this tube is to direct some of the fuel flow to the forward most injector(s).

Some /Most? of the fuel will go around this baffle/redirect tube to feed the rear injectors.

I wonder if the 94-96 fuel rails (with forward cross over) have this ‘baffle/redirect’ tube inside....

Is there some benefit to enlarging that hole slightly (in the baffle tube?) - who knows .....







Front of the rail, showing how the baffle/redirect tube ends (and the end is open pipe) right before the last (forwardmost injector).


Showing how the ‘baffle/redirect’ tube ends (open pipe end) right before the forward most injector.

 

Adding to my prior post:

this photo shows WHY I dont think I want to modify the rails to parallel feed if I dont have to.

i hate the look of these 90 degree return fittings coming off the top of the rails.

Its sloppy looking. Unfortunately it wouldnt be easy to have them come out the SIDES of the rails either bc then it would interfere with the frontmost injector connector.

 

I'm curious how your stock ECM handles 80lb injectors. I'm a little surprised it idles fine on even 60s. One thing you have going for you is that the stock ECM goes to single fire mode at low rpm, whereas the Megasquirt has no such provision. Either I'd lose a bit of efficiency/fuel economy by setting it to single fire, or I halve the already-low idle PWs by setting it to double fire. The point of the FMU would not be to handle the tuning, it's so injector flow is lower at idle and higher where I actually need it under boost. It wouldn't be tuned any different than if FP were constant, except that my VE tables would be skewed so low-load VE would appear artificially high compared to high-load VE. If large injectors will idle well there's no point though.

Did you not have issues running boost on a stock ECM? I feel like it would take forever to track down and recalibrate all of the functions that depend on MAP voltage. For example, acceleration enrichment is based on MAP rate of change. With a 2 bar MAP, it now thinks that rate of change is half what it really is. (For example, a 10kPa change would previously be a 10% change to the MAP sensor output, whereas with a 2 bar MAP it's only 5%.) Or does your ECM have a constant for the MAP range?

I know nothing of the internals of the rail - or even that the TPI rails are similar to the LT1 rails - but I agree that the dual feed conversion looks sloppy. I imagine that if the stock 3/8" fuel line can handle the flow, so can the stock fuel rails. You can make anything work if you throw enough fuel pump at it (until you hit the speed of sound, which would be 80,000 gal/hr with a 3/8" line ).