Bender mid-range lean spot, possible cure.

I was hoping to do more testing before posting this to avoid having to debate it on the forum. However, more and more Bender owners are coming forward with this same lean spot.

For me the lean spot is at about 3-3.5 pounds of boost which is just below 8,000 rpm to about 9,000, or about 1/4 to 1/3 throtle. The lean spot seems to actually more boost related than rpm related. Differrent clutching seem sto move it around on the rpm scale yet it typically stays at the same boost level.

The key is the slides, but with Bender anyway, it is not the springs. The problem is inadequate pressure signal to the slides. Right now you have one line that splits and goes to both of the slide hookups. That single line is not enough. If you take your airbox off and blow in the line you will find it is very restrictive and the 4 slides will not open properly. If you then blow into just one line at a time you will notice that they open with much less effort.

Every turbo and supercharger manufacturer except Bender feeds the slides with two lines.

Despite all of the encouragement on here to try diferrent springs I have yet to find softer springs that fix the problem. The problem is that with the restrictive lines that Bender is using the signal to the slides is to restrictive and not linear. New springs do not make it linear. By the time you find springs that fix this particular lean spot you have affected other throttle positions that were previously fine.

Here is what you do………… On the bottom of your airbox you have two hose barbs one is 3/8 and goes to the fuel regulator. The other is 1/4 and goes to the slides. Start by removing the line to the regulator and relocate it to the four hose barbs between the carbs and motor. This serves two purposes. First, it frees up the signal location on the bottom of the airbox. Secondly, it eliminates the possibility of throttle chop problems.

Next, remove the 1/4 hose barb from the airbox and replace it with a 3/8 hose barb. This requires you to buy a 90 degree 1/8 NPT by 3/8 hose barb. Make sure it is a 90 barb to guard against kinked hoses. Now run one 3/8 line from each of the two 3/8 hose barbs on the bottom of the airbox to each of the slide hookups. Do NOT combine the lines together like they are now. Each line should go to only one slide hookup. Also, do NOT use these lines to supply signal to anything else or it will not work correctly.

We do have three coils cut off of our stock springs currently. That was done before relocating the lines as described above. It did not cure the problem. It did however, seem to improve throttle response. It may be that if you spend enough time screwing around with springs you might finally find a combonation that will mask the lean spot. It appears, however, that the real cause of the problem is the way Bender chose to hookup the slides. Keep in mind that no other manufacturer has been having the lean midrange problems like Bender is having and at the same time no other manufacturer uses only one small line to signal the slides.

Hope this helps.

Here is the jetting being used at about 6500 feet.

130 mains
17.5 pilots (could possibly use larger)
Floats at 17mm
Needles in #4
3 coils cut off of springs.
Relocated slide lines.
300 pitot (this varies from sled to sled)

That is funny I just fixed one like that, I was testing it with a blow gun and noticed the slides open 2 then 2 so I added a second hose.

Didn't do any part throttle testing since it is a drag race application and I thought it was just this one sled being that it is custom.

See I told you it was so simple that you would laugh.

Rereading I noticed you said to hook the fuel pressure regulator to the carb boots, this is a BAD idea, it will drastically lower fuel pressure at idle and light throttle off boost.

The fuel pressure regulator should also be on the airbox on its own fitting and the float bowls go to the charge pipe.

Countless people have moved the regulator to that location to prevent throttle chop problems. So far no one has reported problems.

Did you say the line to the slides was 1/4 " ? .........they must've changed that in later kits , mine was a 3/8 , no probs.

Hey mine is 3/8, i would think it is more of a psi thing than a volume thing with the slides.

Skydog

Spray just got his sizes mixed up on the hose barbs on the air box. 3/8" to the slides and 1/4" to the regulator from Bender.

Ted; You are the one that is wrong about the fuel regulator lines coming from the carb throats. The regulator will not put out less than the static pressure it is set at. Which is around 4 lbs. I have mine coming from the throats and it runs perfectly at Idle and up.

I tried all of this set up that Spray has said in his post. I can't say enough about it. My sled ran perfectly last weekend. I ran trail, straight up hill climbs, straight down hills, and jumping going up hill climbs. Not one stutter all day! People can theorize all day how they think things are supposed to work. There is some "mystic turbo #*$&@" working here in the mountains. All I can say is this set up works. Done!
SS

As long as it works for you that is OK with me.

Most regulators when you put vacuum to them reduce pressure as well as increase pressure with boost.

I never tested this particualar regulator so I don't know for sure just going by experience with other regulators.

Oh goody!! Everyones sled fixed just in time for the McCall ride!!

Silver Streak said:

Spray just got his sizes mixed up on the hose barbs on the air box. 3/8" to the slides and 1/4" to the regulator from Bender.
SS

Click to expand...

I just looked at the hose barbs on my intercooler and they are the same size. Maybe they are different on the stage one kits.

J.

Could be that they changed it. Either way one line is not enough.

After going out and running the sliver Hotzman springs. I am going to try your set up next! The Sliver were not even close! WAY to light. On my set up.

Thank you Skydog P.S. This is mine to the TEE!! (((For me the lean spot is at about 3-3.5 pounds of boost which is just below 8,000 rpm to about 9,000, or about 1/4 to 1/3 throtle. The lean spot seems to actually more boost related than rpm related. Differrent clutching seems to move it around on the rpm scale yet it typically stays at the same boost level)))

Let us know if it works for you!!