Fuel pressure question - NA EFI 347

[94Cobra]

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]

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

[Killercanary]

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]

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

[Balaska347]

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]

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]

Get both Bob. I love the wideband.

[Balaska347]

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]

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]

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]

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]

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]

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]

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]

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]

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]

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]

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]

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]

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

[Balaska347]

Exactly a NA car won't hurt itself from being to lean it just won't make power. A power adder car will keep making more hp as you lean it out until it blows itself up thats why the wideband will help them. For a NA car it is pretty much a waste unless you enjoy watching the gauge. It's all driver preference.

[phillysrt4]

Exactly a NA car won't hurt itself from being to lean it just won't make power. A power adder car will keep making more hp as you lean it out until it blows itself up thats why the wideband will help them.

???

huh?

[Balaska347]

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

The reason I say its a waste is because I bet I could have made the same 435 maybe only 430 without the $900 PMS and a $300 wideband with the car on a dyno with a a/f reading. So I could have saved $1100.

Philly what are you confused about?

[phillysrt4]

Philly what are you confused about?

if a cylinder is lean, it runs hotter. If it runs hotter, its more susceptible to detonation/knocking. If there is sufficient knocking, you can damage your engine.

I just never saw any evidence that NA engines are "immune" to this, or that this only applies to FI cars.

[Balaska347]

if a cylinder is lean, it runs hotter. If it runs hotter, its more susceptible to detonation/knocking. If there is sufficient knocking, you can damage your engine.

I just never saw any evidence that NA engines are "immune" to this, or that this only applies to FI cars.


You're right NA cars aren't immune to hurting themselves but it take a lot more to hurt a NA car. What I was trying to say is that the NA car will lay over first and you will know to add fuel. A power adder car will keep making power until it will usually push out a head gasket or break a piston. Widebands are a nice tool to have but if it was me I would go the other route.

[phillysrt4]

You're right NA cars aren't immune to hurting themselves but it take a lot more to hurt a NA car. What I was trying to say is that the NA car will lay over first and you will know to add fuel. A power adder car will keep making power until it will usually push out a head gasket or break a piston. Widebands are a nice tool to have but if it was me I would go the other route.

ahhhhh ok i see what you mean now.

sorry for the confusion.

[349Stroker]

The reason I say its a waste is because I bet I could have made the same 435 maybe only 430 without the $900 PMS and a $300 wideband with the car on a dyno with a a/f reading. So I could have saved $1100.



I never new chip tuning on a dyno was free!!!!!

and every time you chip tune guys change something it is back to the dyno

Even w/o a chip you still have to go back to the dyno and tune and it ain't free.As for me, I just go out the road and change some numbers

[Balaska347]

I never new chip tuning on a dyno was free!!!!!

and every time you chip tune guys change something it is back to the dyno

Even w/o a chip you still have to go back to the dyno and tune and it ain't free.As for me, I just go out the road and change some numbers


I wouldn't go with a chip either the computer shouldn't need to be touched unless you are having driveablilty issues on a NA car. I will tune it through the fuel psi regulator and timing. You want as much timing you can run without knocking and a a/f of 12.8-13.2 NA. The other thing you want to watch for is a relatively flat fuel curve which it should be with a NA car. To do all this for my car I had $60 in dyno time which everyone wants to see what kind of HP their car is making anyway. And if I make a large enough change that I will be worried about the tune I will be putting it back on the dyno anyway to see what kind of HP I gained.

I called everywhere I could find within 5 hours of here that custom tune through the computer and told them what I have and asked them if they can get me anymore HP they all said probably not or maybe a few. One guy told me oh yeah I see around 30 RWHP all the time so I took my car all the way there and after 6 hours on the dyno he gave me all my money back. If you can get me just 10 more RWHP with you and the PMS I will pay you to tune my car. I just bought a new cam from AFM so I wouldn't mind putting it on the dyno.

[Balaska347]

Oh yeah there is no right or wrong answer here it is basically preference and how much money you want or have to spend. You also have to have the knowledge to tune on your own which a lot of people don't have.

[94Cobra]

Thanks for all of the input everyone. Perhaps I will take it up to Big Shot or another dyno to see where the A/F is at. Oh yeah, and where the power is at as well. If I hit 360/370rwhp, I will be happy and leave it alone.