Fuel pressure question - NA EFI 347

**94Cobra** · 04-09-2008, 09:55 PM

Is 46 too high with all the vacuum lines connected? My car idles the best, makes the most vacuum at idle, and drives just fine at 46.

I have 42 lb injectors, 90mm LMAF. My car has a custom tune for my old NA 347. My new combo has a AFM-B41 (old was TFS-2), new Systemax 2 (old was TFS R Series), new Hooker 1 5/8 super comps LT's (old BBK eq length shorties).

I know the 42's were adjusted way down in the custom tune for the old combo. The tune is the same, but the new combo seems to like 46. I wanted to find out if 46 could cause rubber fuel line bursting or other problems. I'm taking a long drive up to U'town for some work by Tim this Saturday. I don't want to have any problems. Thanks.

**Viper_ed** · 04-09-2008, 10:11 PM

I'd say you're fine. I always set mine around 44 psi.

**Killercanary** · 04-09-2008, 11:32 PM

You don't need to worry about bursting anything. Any car that you have seen with a blower and an FMU is likely seeing 60-100psi under boost. I'm running 45psi base pressure on my 331 with 24's. Unless you pulsewidths are very small via the chip, that seems like an awefully lot of FP to be running with your combo and 42's. The only way to know is via a wideband.

**wick** · 04-10-2008, 06:23 PM

Yeah, Paul is right. Under boost, I am getting real high pressure. Just need to get that tune real soon. HAHAHA

**Balaska347** · 04-10-2008, 06:32 PM

Yeah you definitely won't hurt any except for HP. Thats a lot of fuel for that combo. I would bet on a dyno your A/F would be down in the 11.0 range if not lower.

**94Cobra** · 04-10-2008, 07:32 PM

Now you have me thinking I should lower the fuel pressure. I pulled a spark plug and the insulator was real white, but with the hotter ignitions you can't tell much by that. I am debating whether to get a wideband or a new tune - they both cost about the same price.

**wick** · 04-10-2008, 08:00 PM

Get both Bob. I love the wideband.

**Balaska347** · 04-11-2008, 06:18 PM

I run all most the exact same setup as you and just to let you know it will take a really long time to turn the plugs a different color. When I changed the combo around a little I just put the car on the dyno with a A/F reading to get it where I needed it. I have 30 lb injectors and with the fuel psi at 42 lbs the a/f was 12.9. If I had 42 lb injectors I would have to run a lot less psi to keep the 12.9 because of the larger injector. You don't need a wide band unless you are going to run a power adder you would be wasting your money . Your best bet is to just put it on the dyno.

**phillysrt4** · 04-11-2008, 07:30 PM

The wideband versus a dyno tune is a tough choice. I would ask myself the following questions:

1) Do I own a device like an SCT tuner that will let me do my own tune?
2) Do I understand tuning and how to apply it to my setup to have a successful tune?
3) Is it important to me to make sure everything is monitored so that if something should go awry (e.g. regulator goes bad, fuel pump starts to fail, injectors get clogged, etc) I know about it immediately?

If you can answer yes to these, then going with the wideband might be a better choice than getting a tune on a dyno.

My understanding of tuning on the dyno is that the dyno only serves to give you an air fuel ratio while getting the car to run under load. If you have a data-logging wideband where you can capture the data for review and a nice big steep hill nearby (those of you near Mt. Pleasant have 3 mile hill, for example) then you have an easy substitute for the dyno.

Whether or not you choose to get a tune on a dyno, having something to monitor the air-fuel in daily driving conditions justifies having a wideband anyway IMO.

**Balaska347** · 04-11-2008, 07:43 PM

With a N/A motor, unless you get really crazy with setup, you don't really have to custom tune with the computer. Your not gonna benefit like a car with a power adder. All I did was paid $60 for three pulls on the dyno and between each pull I adjusted the fuel psi until I got the a/f ratio I wanted. With a N/A motor most people are running a/f ratios between 12.8-13.2. If your a power adder you want 12.0 or high 11's to be safe.

A custom tune with a N/A motor will get you driveablility and maybe a handfull of HP depending how far off you have your timing and fuel. I don't think it is worth the $500.

**fastfox91** · 04-11-2008, 07:57 PM

a wideband is never a waste of money at least in my opinion, with a car that is run hard, like said above u never know when something will happen and it is a great indicator of performance problems.

**fastfox91** · 04-11-2008, 07:59 PM

by the way ill make a suggestion as far as a brand, and that is a aem, they are cheap and work great, a brand new one can be had for right around 230 dollars.

**94Cobra** · 04-11-2008, 11:47 PM

Thanks for the input. I do know the pulse widths were turned way back on my 42's when I had my custom chip burned for my old combo. I'm guessing that is why I can get away with 46psi. I do like the idea of having the A/F monitoring, but I don't want to put a big gauge or box in my interior. I will have to check and see where/how the a/f gauges are mounted.

**fastfox91** · 04-12-2008, 04:56 AM

the aem is just a 2 1/16 gauge and it has removable faces and bezels so u can pick which u like best

**349Stroker** · 04-12-2008, 11:24 AM

any reason you chose 42's?

I'd go back to 30's and retune

I had a more agressive setup that what you have and 30's were plenty

Just something to think about

This is why I like a pms and wideband because if you make changes you don't have to go runnig back to the dyno all the time,just change some numbers and go but to each his own.A dyno tuned car works fine too

**94Cobra** · 04-13-2008, 06:59 PM

Originally Posted by 349Stroker

any reason you chose 42's?

Don Lasota, my 1st tuner told me he could tone down the pulse with the tune so the 42 were no big deal. Also, i got a great deal on the 42's and 90mm LMAF for $349 through buyfordracing.com.

I've thought about the pms as an option. Rick A. told me the PMS will not allow me to tune out the hanging idle that occurs when you put a cam in the 94/94 cars. You also cannot turn off the CEL or disable the EGR functions via the PMS. I would probably go with one if it had more flexibility in those 2 areas.

Rick A. also told me the LMAF won't work with his PMS so I would need to buy one of those.

I assume you are happy with your PMS. Do you have an aftermarket cam and any hanging idle problems?

**Balaska347** · 04-13-2008, 09:10 PM

Did you ask Rick A. about a wideband for a NA motor? He will tell you that you are wasting your money. He knows what he is talking about.

**94Cobra** · 04-13-2008, 09:15 PM

Originally Posted by Balaska347

Did you ask Rick A. about a wideband for a NA motor? He will tell you that you are wasting your money.

No, but he did tell me that an NA car will lay down if it runs out of fuel and that I won't hurt the engine even if it did.

**349Stroker** · 04-13-2008, 10:06 PM

Mine being a 88 I don't have an idle issue like yours

I have a B41 in my car as well but I am runnig a 306 with an S trim now.

I had a stage 3 trickflow cam in my 349 and it worked great

Yea the 90mm meter wouldn't work.I use a 95mm PMAS velocity

**349Stroker** · 04-13-2008, 10:09 PM

Originally Posted by Balaska347

Did you ask Rick A. about a wideband for a NA motor? He will tell you that you are wasting your money. He knows what he is talking about.

I can't see how it is a waste.Still have to tune a N/A car and my pms and wideband did great on my 349

That made 435 rwhp at 12.2 a/f

The guy I sold it to dynoed it and got those #'s but hasn't been back to thre dyno since to lean it out.I never dynoed the car I just tuned it with pms and a wideband