elkabong

I thought there would be interest in this. I have been struggling with feeding a 383 in my 84. On the dyno we noticed a fuel pressure drop from 20psi to 15psi with a TPI pump. Pressure started to drop off from 4000rpm to 5500rpm the pressure was at 15psi. Needless to say this indicated a severe fuel delivery issue - the TPI pump should be able to supply enough fuel - I have a LT1 pump in the wings just in case the motor needs more fule. One way to cure this is to parallel plumbing the TBs. The regulator is a bypass regulator hooked up to the return side. I am also removing both regulators and will have a plate welded in place. The injector tops are at the weld shop and should be done in a couple days. Hopefully this setup will supply enough fuel to feed the motor so it can be all it can be.

I also plan on redoing the fuel lines to use hardlines once I get stuff setup. This was a exercise in getting it plumbed and working. The airpump at this point is nothing more than a pulley - it is gutted. I may fab up a airpump delete for the 84 sometime in the future.



"To boldly go where not many are willing to tread.."

comp

what where the dyno #'s ?

elkabong

286hp and 312 tq to the rear wheels. The motor should be capable of 330-350hp to the rear. Once I get the fueling solved I can finish the tune.

comp

keep us updated

CFI-EFI

Something is wrong with these numbers. I have a 350 running 14 psi of fuel pressure. I get ZERO pressure drop to and through 6000 rpms. You have 9 1/2% more cubic inches to feed, but you think you need 42% more fuel pressure to feed them? Can't you tune the pulse width for more fuel? Use larger injectors? What's wrong with these numbers?


BOTH REGULATORS? What do you have cobbled up in there that uses two fuel pressure regulators?

This doesn't add up. Possibly your fuel filter or sock are clogged and can't handle the volume. A, supposedly freer flowing fuel system, after the pressure gauge, should show up as an even greater pressure drop. There is no way you have increased the fuel needs of the engine to require such a drastic overhaul of the delivery system. It should, however, cause no harm, so maybe such a diversion will keep your "tinkeritis" from doing any real damage.

RACE ON!!!

elkabong

The calculated numbers show two injectors need to flow 114.29lb/hr to support a hp target 413. The way to do that is increase the fuel pressure. I am also using 80lb injectors. The flowrate of the injectors have been validated on a flow bench.

Yes I can program the injector pulse width. The trick is keeping them to a 80%-85% duty cycle - hence the higher fuel pressure to support the flow requirements and duty cycle requirements. Headroom is factored in as well. Running them static or close to static is not a good thing.

I mis-stated the "regulators". My humble apologies. The front TB is the accumulator and the rear is the pressure regulator. Needless to say they will both be blocked off.

As far as pressure drop is concerned I have no doubt you do not experience the same things that I am. There is a big difference between a stock motor (205hp, yours is stock right?) and mine which should be capable of 375hp-400hp. Needless to say the fueling requirements are extremely different. All I know is what was seen while on the dyno and what the data logs show.

No "tinkeritis" here. Just being rational about the whole thing based on data - not supposition or inference.

CFI-EFI

I haven't checked all the numbers, but they appear reasonable at first glance. When you say "The flowrate of the injectors have been validated on a flow bench.", are you saying that the 80# injectors have been verified to flow 115# at 20 psi fuel pressure? That seems like a helluva stretch from the specs.



The "I am also removing both regulators..." comment had me doubting your knowledge.



Yes. Except for the ported stock intake casting, my engine is all stock.

I guess before I can comment further, I would have to know where you are taking your fuel pressure measurement from. I have been assuming, picturing, one thing, which I can see now, may not be the case.

RACE ON!!!

JackDidley

Makes sense to me. Stock tpi pump has its limits. A few years ago, on the dyno my tpi car was making nearly the same HP (lots of torque though) while datalogging and watching the pressure guage I noticed a pressure drop at the same time the wideband said "lean" and HP dropped off. Time for a Walbro.

CFI-EFI

Indeed, the TPI pump does have it's limitations, as all pumps do. A drop in pressure is an indication of an insufficient fuel supply, as you experienced. However, parallel plumbing of the TBs neither increases the pump output, nor reduces the fuel demands of the engine.

RACE ON!!!

JLeatherman

It may be he's experienced a drop in the pressure BETWEEN the TB's as referenced from the input pressure at the regulator. Parallel plumbing would help that.

Glad you've got the new motor in Elkabong.

flannel_man

elkabong

The pressure is measured on the input side at the Y block and regulated going back to the tank. Regulation still takes place on the return side.

CFI-EFI

Before my first post, I was "***-U-MEing" the pressure reading was coming from the input to the first TB. After my first post, it occurred to me that he might be measuring the pressure between the TBs, as you suggest. That is why I backed off and asked.

RACE ON!!!

CFI-EFI

If you are getting a drop in fuel pressure at the "Y" block, as the engine revs, then the fuel system isn't delivering the goods. You have a supply deficiency. Either the pump can't deliver, the sock is clogged, the fuel lines are too small or the fuel filter is too small or clogged. The parallel plumbing will do nothing to alleviate that problem.

RACE ON!!!

elkabong

The pressure drop was in the stock configuration measured at the line between both TBs. I will let you know whether or not parallel plumbing solves the problem once it is back on the dyno. Also, data logs will also show whether or not it is working because the duty cycle of the injectors should not spike if enough fuel is being supplied.

JackDidley

I wonder if 280 rwhp is past the limit of the pump? I am not familiar with the CFI system or its requirements so I don't know about the delivery needs. I ended my story with, "time for a Walbro" as a suggestion to Mr. kabong. I would like to hear updates on this motor, because I like to see guys do something different. Even more when they have success.

Demonic85

It sounds like the TPI pump cant handle the upgraded 80 lb injectors if all is flowing well otherwise. Maybe you could try one of those upgrade Walbro pumps.

elkabong

Mr. Spanky ,

I have a high flow pump in the wings just in case. The assertion that the TPI pump can't handle the fuel requirements may be correct but I would like to find out. I have a buddy with the same TPI pump on a MPFI equipped motor putting out 400+ at the crank. So who knows..... The other thought is the TPI pump just may be toast and not up the challenge.

FWIW - Parallel plumbing both TBs has been used since '02 so it is not new in the Crossfire world. All one needs to do is go to http://www.crossfire.homeip.net/ and search for "parallel plumbing". Also, it is all an experiment anyway especially with the 'ol Crossfire.

Demonic85

Here's a good deal for ya.

http://forums.corvetteforum.com/show....php?t=1692492

elkabong

Thanks for the thought but that pump is for a Mustang as stated in the post. As I mentioned, I already have a new pump in the wings just in case.