ptuomov

The noise is definitely coming from the fuel pump. By low frequency I mean that my recent improvements were successful in reducing higher frequencies, but the relatively lower frequencies remained.

I suspect that the sound is using the fuel tank as an echo chamber.

It's not the cover, the pump is about as loud with the cover on vs. off.

As far as I can tell, the pump is properly mounted on the stock bracket which is isolated from the tank with the stock rubber bushings.

I put a mass loaded vinyl sheet on top of the foam and under the mat in the trunk, which worked in reducing the exhaust noise a bit. It didn't reduce the pump noise much. Therefore, I think the sound must be coming thru some other channel.

ptuomov

The problem with dual Bosch pumps is that making a pickup and hoses that
(a) seal
(b) don't touch anything to transmit the sound
(c) don't collapse at high radius bends
(d) fit
(e) can be tightened with the straps on
is nearly impossible. I say nearly because maybe Hacker's friend Todd has managed to do it.

The Fuelab pump can be controlled with a pwm logic signal. Before I start wiring that up, however, I have to be sure that the plumbing is in its final configuration.

ptuomov

I am running it at the low setting, and still circulating too much fuel, heating the fuel, and the pump is loud.

I should probably try it at 100% speed to hear what it sounds like then!

hans14914

Tuomo,

The internal (non-PWM counting) controller is relatively stupid - It lets you toggle between several different speeds, but I didnt know if you had gotten clever and used a relay tied to the WOT switch to cycle the pump between full output and low output modes.

I am not sure a smaller pump would have helped with the noise, but it sounds to me like you may have over speced your pump a bit there. Of course its only opinion, and you know what they say about that, but I think that you really are a candidate for a 41xx pump, and didnt need to be in that 42xx bracket. I am not sure much consideration goes in to noise control on all-out pumps like that, so not sure you will be able to get it down to a streetable level. If you were running a smaller pump like the 41401, then you woudl probably be able to get away with a bit lower noise as well as reduced heat injection into the fuel supply (you could also go with a "dumb" controller loop, and set the pump to go full supply under WOT and during cruise and idle it would run in the low output config - no PWM programming required).

Call the guys at Fuelab, and see if they have any recommendations, but I think you are kind of stuck. Sorry the lack of suggestions, I just think its a side-effect of such a massive pump.

ptuomov

My original idea was to go with a relatively oversized pump but then control it intelligently from the MAF signal and/or rpm. The idea was that the large pump would be quiet and reliable at low rpm. This is still the plan, but the pump is much, much noisier than I expected at reduced speed. I am think that I must have made some rookie mistake mounting it and the vibrations are transmitted thru some channel into the tank and the cabin.

BC

Well, I was just to the point of getting one, and at about the same spec as yours Tuomo. I was planning on running the pump with PWM, but if you are on the low setting, and pumping too much fuel (and returning too much heated fuel) then we may be able to learn something from you.

Can you isolate the MOUNTING of the pump more?

I agree with Hans, - in that I am not so sure a lesser rated pump would be THAT much quieter.

ptuomov

The PWM signal can control the pump at much lower speed than the constant "low" setting. The pump turns on at 20% duty cycle and reaches maximum at 90% duty cycle. The constant "low" setting is probably equivalent to something like 65% duty cycle. One should be able to run the pump much slower most of the time than 65% duty cycle.

I called the Fuelab guy. He was very helpful, although possibly a bit offended by my suggestion that his pump is too loud. He said it's not loud, competitors pumps are much louder, and that he has the pump running in shows and he's having a conversation within two feet. My counter to that was, yes, you better be able to have a conversation when the pump is on! I guess we have different standards.

I explained to him my future plans and he said that the pump is sized about right for my application. He said that his smaller pumps are quieter "obviously," but he said that it's not easy to say whether small pump at high speed is quieter or louder than a large pump at low speed. He also said that mounting is usually the key with noise, which I, of course, agree with.

I guess the next step is going out there with the mechanics stethoscope to look for potential sound transmission channels. I am guessing that it's somehow transmitting the vibrations to the tank, just can't figure out how.

BC

I didn't know about the PWM allowing even lower power. That may help you.

ptuomov

Got some leads with the stethoscope. Some things are very loud when listened to with a stethoscope.

The tank vibrates with sound, but less so than I anticipated. I don't think it's the tank.

Here's my theory after touching a lot of things with the stethoscope tip. The stainless hose from the pump's pressure side is loud as hell, and transmits the vibration to the stainless hard line. The hard line goes around the fender well, and gets a nice echo. As a result, the entire right rear quarter panel is vibrating with sounds like crazy. The quarter panel itself is fairly well insulated from the cabin, but somehow the vibrations get transferred to the window. The window has no insulation and broadcasts the vibrations to the cabin.

To test the theory, now is the time to get some rubber hose to the pressure side of the pump. I need to find some high quality rubber hose without those stainless braids that is fuel safe and can take the high fuel pressures. In other words, I have to take a mulligan on most of the last years weekend's work. Oh well.

Bill Ball

Wow! I thought George's 100 gph (1000 HP) Aeromotive was overkill. Even at 120 gph you'll have real problems with gas heating up unless you drive around at WOT all the time and keep the tank full. Once it gets below half full, the gas will heat up quickly if you are doing any normal driving where probably 90% is recirculating. That speed controller will help a lot. We just put one on George's Aeromotive today.

Bill Ball

Oh, another critical variable we learned about when trying to understand George's fuel heating and pump cavitation problem is to have very low/no fuel return line pressure. With all the fuel you are trying to shove back through the the stock fuel return line, if that is what you still have, there is a lot of trapped aeration of the fuel which increases the risk of cavitation, and there is more heating of the fuel as well from resistance in the line. The return line need to be larger than the supply line. In George's car we ended up plumbing AN10 all the way to the front for fuel delivery and we T'd together the original supply line with the fuel return line, basically doubling return capacity. We're using a fuel cell, so it wasn't hard to double-plumb the return lines into the cell. Anyway, look how small the return line fitting is at the top of the tank and you will see the problem this causes with HIGH flow fuel pumps like you have.

http://www.lmengines.com/fuel_lines

ptuomov

After last weekend, the system works surprisingly well. Other than being too loud. I tested running it for about an hour with the low fuel warning light on, adding just a gallon of fuel at the time. It doesn't seem to cavitate anymore and the pickup side hoses are not collapsing etc. Of course, if I churn and heat the fuel for hours before the tank runs low it might be a different story.

My -10AN pressure line equates to about 2 fps fuel flow velocity at 120 gph. I am using the stock return line. Now, you might think I am crazy to do that, and maybe you'd be right! ;-) When I return the entire 120 gph thru the stock return line, the pressure after the regulator should be about 6 psi gauge. The numbers come from the calculator in your link.

My theory was that I am going to run the fuel pump controller from the MAF signal, which would lead to extremely (in theory) accurate metering of the fuel and very little fuel being returned to the tank. Thus, the stock fuel return line should be enough. Let's see if I get this done.

jorj7

Last year before the September Silver State Classic I was running a Fuelab 41402-c fuel pump wired for
low speed mode. I down graded to the Aeromotive A1000 (11101) to decrease the gas flow for the
Bonneville 100 this year, but still was overheating the gas. As Bill said we just upgraded the feed and
return lines and added the Aeromotive pump controller (16306). I sure hope this will take care of the
problem. Racing at 6,000 feet in 100 degree temps don't help either...

ptuomov

Did you try the Fuelab pump pwm control mode? In theory, that should allow one to pump very little or a whole lot. I don't know about practice, yet.

333pg333

Just curious if you've done any modifications to the suspension and brakes to cope with all the extra power?

One of the major problems for the high powered 951 folk is headgaskets. This could be for a number of reasons. Peak cylinder pressure could be the killer. Also having the 'floating' cylinders on the 2.5L block instead of the 'siamesed' bores of the 3L block will probably be a contributing factor. Running more boost compared to most of you guys will create issues too. There are a few guys running 35psi on their street cars for example. All on E85. In fact these guys haven't had h/g problems yet. Those of us who frequent the track are more likely to suffer under continual loads by comparison to street squirts.

Great build and thread. Not all of us are scared of you Big Bad Boyz in your 928s though heheh.