I am trying to optimize my hardware before I get into chip tuning. I am trying to determine the fuel requirements for a 300FWHP engine. My current combo made 210 RWHP with a really bad tune and old sensors and HEI module.

I have since replaced all of the sensors and HEI module and car is much more driveable and has much more power, at least at part throttle. It still doesn't like to rev much past 4,000 RPM, which I suspect is fuel related. My assumption in this discussion is that the engine will/can make around 300 FWHP.

Now to the math:

Using 300FWHP and a .50 BSFC (obtained from Aeromotive web site), I get a fuel requirement of 150 lbs/hr.

Adjusting for an 80% duty cycle, I would need two injectors that could deliver 94 lbs/hr ((150 lbs/hr / 2 injectors) / 80% duty cycle).

I currently have two 65 lbs/hr Corvette injectors, where the flow based upon the stock 13 psi fuel pressure. In order to flow 94 lbs/hr with these injectors, I would need to crank the FP up to 27 psi, or almost double (I had to back into this result using the formula: SQRT(27psi new/13 psi old) * 65 lbs/hr old = 94 lbs/hr new


This does not sound like a good thing. Or is it? I remember reading about regulator diaphrams rupturing under high FP. I have read of marine or 454 injectors with higher flow rates at lower fuel pressures (80-90 lbs/hr at 20 psi, maybe??).

Which is better? smaller injectors, higher FP or bigger injectors, lower FP?


With respect to the fuel pump, I am going with a 190 lph Walbro replacement pump. This seems to be plenty for my target HP.

Currently running a 1226026 computer, but am working up an EBL powered 7747.

 

How big are your TB's??? If you still have original TB (1-13/16") they may not flow enough air to support the HP goal that you are seeking. For HP level it is probably wise to upgrade to 90lb BBC injectors with VAFPR to keep things happy at idle. Check with Fast355 - I think he has 2" BBC TB on top of a very hot 350 getting some serious power.

//RF

 

Sorry, I thought that info was in my signature. I have 2.1 inch throttle bodies.

Based upon your response so far, it sounds like bigger injectors with lower pressure is the preferrable route. I did see some threads where it was discussed that the EBL upgrade had the programming to support a VAFPR.

 

IMO go with the smallest injector that will fully fuel your engine @ 32 psi. I shoot for 28-32 PSI @ WOT on my TBI engines. I have run the stock fuel pressure regulator continously at 40 psi, WITHOUT failure. When the pressure goes to around 55psi, the diaphram typically , not good. I ran over 20K miles at 40 PSI and no ill effects, other than noisy injectors. Some of the stock TBI trucks and boats ran at 28-32 psi.

 

Fast, I have read that high fuel pressure causes some people to have idling problems. I assume that is tunable?

Also, are you still in Hurst? That's not too far from me in Dallas. Are you a member of any local clubs where we might meet? Would love to find someone local with some FI tuning experience to share. Right now I'm on my own with input from the boards.

 

check this out

http://www.users.bigpond.net.au/ben_...ctorsizing.xls

you can check HP your injectors will support at various FP CID etc. calc BPC also.

I experienced idle issues with 80 lbs at 22 lbs FP. Issue was asynch mode in open lloop. I disabled asynch mode retained OL and dropped FP to 20 lbs.

Still planning on using the VAFPR I have installed but been without lappy till today !!

Now I just realized the OL idle or TPS at 0 % in deacceleration is different for 7747 vs 8746? So I read past week. I have EBL'd 8746. Not sure if EBL has an advantage as far as idle quality. My idle has never been better at 800 rpms with manual.

 

Just noticed your setup is very close to mine a couple years back. Heads cam x ram 2.00 TB ext etc. I would not expect car to run very well without serious tuning. Adding a GM Marine VAFPR was a no go. Mine flat out was not drivable. I would get a Moates USB cable and get a datalog(winALDL) of BLM to start. It will confirm how far off the tune is with stock Vette ECU. I tink my BLMs were pegged lean at 160 maxed out in some areas. I threw a lean code cruising at 35 mph.

 

Actually, the car is running pretty well on the stock 6026 Vette ECM. However, I know it could run much better. I bought the car from my brother and know he had trouble with the guy that did the 350 swap. I was fixing stuff the guy screwed up at the same time I was trying to tune - just was not working.

Most of the electronics appeared to be original, 25 year old stuff so I replaced all of the critical stuff (HEI module, coil, TPS, coolant temp sensor, MAP). Car already had new TPI pump and injectors (stock 350). The car ran significantly better afterwards.

The car is currently in the garage with the TBs off. I bought the Moates cable and downloaded WINALDL. First thing I noticed was that the TPS sensor voltage was way too high. Car was idling at 950 in park, adjusted the TPS to spec and idle shot up to 1,500 in park. Must have a big vacuum leak somewhere.

Took off X-Ram top and noticed that gasket between manifold and X-Ram top was torn, but pieced back together by the person that did the install. I pulled the rear FP regulator apart to remove the anti-adjustment plug and the wrong spring was installed in the TB - guy switched springs when he rebuild the TBs.

Everything cleaned, tightened up and back together. I also installed a stiffer spring in the rear FP regulator (will probably remove stock FP regulators and go with a single external regulator once EBL is installed, will keep TBs plumbed in serial).

I did drive around and do some data logging before pulling everything apart. BLM wide averages were over 128, mostly in the 130s with a few 140s. Some of the BLMs in the low MAP area were below 128. In short, they were all over the place. WOT wasn't great either. Motor starts to sputter at about 4,000 RPM - I'm pretty sure its for lack of fuel.

Hoping to have a new EBL Flash in about 2 weeks. This is my first FI car to try and tune. It's been challenging getting up to speed, but these forums really help. Can't wait to start tuning. I would REALLY like to get a bigger cam to make some more power.

 

Very nice summary.
To keep everything safe I would add fuel - since all of your BLM's are above 128 - ECM is adding fuel over baseline (except for low KPA, idle). Compared to stock C3 ECM EBL offers massive opportunity to adjust and tune. Just make sure that you follow the basics first and maintain a notebook of changes.
BTW do you have KS functioning???
Regarding Idle - reset IAC - there is a sticky, and yes check for vacuum leaks.

//RF

 

Yes I believe the KS is functioning. I currently have what I suspect is the original engine sensor and the original ESC under the dash (parts same as '82 Vette). Since I am running an 84 computer, I bought an 84 Vette KS and ESC. However, both parts are different from the 82 version - the KS uses a different electrical connector and the ESC is much smaller with 4 wires vs the 82 with 5 wires. I believe GM mounted the 84 ESC under the hood in the Vette. I know the 84 parts can be used, but I have other things to worry about first.

I did get knock counts when I was data logging, but it is a consistent number among different RPMs (i.e., like 4 counts at 2000, 6 counts at 2,500). I believe the counts are from the exhaust leak I have on the passenger side header at the collector (very close to KS). That will get fixed after everything is back together.

Also, I am installing all new vacuum hoses - all of mine are original

I will be installing an FP gauge and fine tuning the fuel pressure. I think I am going to set it at stock initially (13 psi) and then datalog again with the stock computer to see where everything winds up. Then I will switch to the EBL Flash ECM. I don't want to make the ECM switch until I feel all of the hardware is up to snuff.

Ronny, thanks for the link. I had actually already created a similar spreadsheet to calculate injector numbers. I didn't have the BPW calc though.

 

With the parts mixed up previously, it may be good to check the injectors. The TB with the accumulator receives a larger flowing injector then the TB with the FPR. If you want to run the same injectors in both TB's, and get the best possible fuel distribution from the injectors, set up the fuel lines in a parallel arrangement.

Block off the stock FPR and accumulator on each TB. Bring the feed line from the tank to a T and plumb in parallel to each TB.

Bring the return line from each throttle body to a remote mounted FPR, then back to the tank.

Try to keep the line lengths to/from each TB the same as the other. Both feeds the same and both returns the same length (as best as possible).

With the external FPR you can then also run it vacuum referenced (VRFPR). This has the fuel pressure changing as the manifold pressure changes. Lower manifold pressure, lower fuel pressure. Will need to run at least 18 psi of fuel pressure to use the VRFPR (and the EBL to handle it). Running a VRFPR setup makes the engine more responsive.

RBob.

 

RBob, thanks for the input. The FP regulator topic was one I wanted to discuss with you once I was ready to install the EBL. I looked at the injectors and they appear to be rebuilt GM (too clean to be originals). Both injectors have the same part number (5233775).

Please forgive the dumb newbie question, but what is the accumulator or compensator? People have mentioned these terms in other threads. I have both TBs in front of me and cannot see ANY difference in the FP regulator assemblies other than one regulator is adjustable and one is not. The castings look perfectly interchangeable.

May be this explains something I noticed before I took everything apart: the fuel spray from the front injector looked pretty coarse with relatively large fuel droplets, maybe what you would expect to see on an old, dirty injector (but it is new). The rear injector had a nice finely atomized spray. The difference in spray was very noticeable.

I initially thought this was due to the FP regulator spring mix up, but not sure now. Am I missing some parts?

 

The 5233775 injectors are the 5.7l fronts. The rear being a 5233770 injector. They are in the area of 67#/hr.

The accumulator is basically a FPR without the plate to close off the orifice. It just buffers the fuel pressure to the one TB. The spray should be as you mentioned, finely atomized. Don't know if the difference you see is from a fuel pressure difference. Could swap the two injectors and see if it follows the injector.

RBob.

 

I pulled FP regulators open again and I see.

I've been reading threads on the CFI Vault site too. It seemed like a couple of people had concluded that you could keep the TBs plumbed in serial when using the TPI pump. I think the reasoning was that the increase in volume/pressure with the TPI pump was more than enough to cover up the slight change in pressure to rear FI (from front FI firing) normally seen with the stock lower volume/pressure pump.

Was that conclusion proved incorrect?