The Stovebolt Site Forums The Shop Area The HiPo Shop Holley Sniper install on a 235

Joe H,

That’s impressive fuel mileage, I hope mine will match that after I’m done tuning. You’ve got an advantage though with that rear gear ratio.

My AFR for idle and cruise are on the rich side compared to your numbers, I’ll need to adjust them. WOT is the same as yours.

Thank you for the feedback, that’s exactly what I’m looking for.

JW51,

Good question. I’ve read or been told (my CRS is kicking in) trying to read the plugs with our modern ethanol gas is a waste of time.

That being said, once I get my AFRs set and drive it a few hundred miles, I plan on pulling the plugs to have a look see.

JW51, you are 100% correct, the manifold design is terrible for even distribution on an inline six. V8s are much better, but the intake type will determine just how even the cylinders are. I know race engine builders alter the jetting in the four corners of the carburetors to help even them out.

My manifold on the 250 inline six has dual carburetors spread apart to feed three cylinders each. I can see the difference in fuel ratio's with a very slight turn of the mixture screw of one or both carbs, so the gauge is very responsive to changes. I recently installed the stock intake and single Monojet carb just to see how it compared to what I had been running. The Monojet was a stock rebuild by me that came on the engine, the fuel ratio was off the gauge lean. It ran OK but not great. I raised the metering rod till the fuel ratio came down below 17:1. It ran pretty good, but I could smell the rich exhaust and fuel mileage was way down. I have three of the same carburetors, so swapped them around and all three ran about the same, jetting was very close to each other. The manifold design was creating the lean conditions, the outer cylinders run much leaner then the inner ones. I didn't need to check plug color to know what was happening, didn't run it long enough to color them anyway. Last weekend I went back to my dual setup, The truck is much happier now! An infrared heat gun reading exhaust manifold temps will show you the same thing, the outer cylinders are always hotter.

Joe H

How about some pictures of your current set up?

Sounds interesting and I’d love to see it.

UPDATE

I’ve got a little over 500 miles on the truck since the EFI install. So far so good, no operational issues and no intake icing has been observed.

I have adjusted the timing and the AFRs. I’m averaging 14.3 MPG. I do very little hi-way driving with my normal drive being to town, 5 miles away. Now that I have some miles on the EFI and have confidence in it, I’ll get some longer leg hi-way miles on it and see if the mileage improves.

Since lead additives in gasoline got eliminated by the tree huggers, plug checks are pretty much a waste of time. The "tan to chocolate brown" we used to look for 50 years ago has literally been replaced by "black and white". Way rich is sooty black, and virtually any other mixture doesn't do any color change until extremely lean conditions start to glaze and blister the ceramic, and the ground electrode starts to burn away. What we were looking at back in the dark ages was varying degrees of lead deposits making the surface of the porcelain change color.
Jerry

14 mpg seems pretty darn good, especially for non-highway driving.

Keep the updates coming. Cool project.

Just a quick update.

The Holley Sniper is working great so far. I have not experienced carb icing. Mileage is consistent at 14 MPG.

I do have one issue, the Holley in tank fuel pump is loud. Fuel pressure is a solid 58 PSI as indicated on the fuel pressure gauge located at throttle body. I’ve reviewed the Holley fuel pump forum which blames a loud in tank fuel pump on pump cavitation. I don’t think that’s the case with my pump as I have a new 100 micron sock on the fuel pump, all new fuel lines and a new 10 micron filter before the throttle body. Fuel pressure is rock solid at 58 PSI and I have no performance issues. I did drop the tank and pulled the pump to inspect the sock and overall pump installation, which all looks good.

Any of you fuel injection guys experienced this issue and if so, whats the fix?

Does that carb. require that much fuel pressure?

Ed

It's not a carb. It's a TBI, so yes, it does require that much pressure.

Pretty plumbing!

Is your fuel tank behind the seat?

The shared intake ports allow complete separation of A/F into cylinders 1-2, 3-4, and 5-6... with 3 throttles, not 2.
Moving the carburetors apart is probably an improvement, but the 3-4 port is still fed by both intakes.

As to ratios: it's nice to know what number you have, but without individual sensors it's just an average, and no way to tell whether the cylinder-to-cylinder deviation is 1% or 20%. Even with 13.8:1 on the display any cylinder may be borderline lean (16:1) and knock under high load. You have to adjust for what the engine tells you, not a number. If all cylinders had the same A/F 13.8 would be way too rich for high vacuum cruising, 15 and up will give better mileage.
Does the Sniper have vacuum input as part of the fuel control? Are you using vacuum advance at the distributor? Adding advance without leaning the mixture won't help mileage.

Most OEM EFI pressure is 43.5 psi.

JW51, I’ve moved the fuel tank from the cab to under bed aft of the differential.

Panic, The Sniper does not use vacuum input as part of the fuel control. I am using vacuum advance at the distributor. The Holley Sniper EFI Installation Manual calls out 58.5 PSI for operating pressure. The install manual also states that the AFRs displayed on the controller are averages.

My fuel tank is vented using a TANKS Inc roll over valve mounted above the tank. With the engine running I’ve removed the fuel cap which does not affect the noise the pump is making, so I’m pretty sure the tank is vented properly.

Does the volume change with the temperature or with the amount of fuel in the tank? The walbro I have in my truck is louder when it is hot outside, but not annoyingly loud.

What kind of sound is it? And how loud is it compared to the exhaust?

Fibonachu,

No change with temperature.

It’s annoyingly loud, whistle type noise that starts as soon as I turn the key on and prior to start. It then continues as long as the engine is running. My truck’s exhaust is pretty quiet and I can hear it in the cab while driving.

Fuel pressure is rock solid and engine performance is great.

I’m beginning to think I have some kind of vibration/harmonics happening in the steel fuel lines that run from the tank area and along the frame rail to the engine compartment. When feeling the steel pressure line it does have a slight pulse. I’m going to get under the truck today and see if I need to add some clamps to the lines and see if that helps.

I read somewhere (I think on the Holley Forum but can’t find it now) that having the in tank fuel pump internally regulated to 58 PSI and the Sniper unit itself internally regulated to 58 PSI can cause a noise as the two regulators are fighting each other. The fix is to remove the regulator from the in tank pump somehow. Have you heard of this?

DB, I installed a 4 brl Sniper EFI on my BIL's 57'. The fuel pump on it was extremely loud(loader than the flowmaster mufflers) and had an issue with keeping up with the engine under load. I found that the return line was restricting the flow and causing the pump to cavitate. I relocated the return line to the top of the tank, actually in the filler neck and remounted the lines (the tank has no access point to attach a return line). Since that point I have had no issues and the pump is quieted down considerably.

Excellent info, thank you. I will give that some consideration. Did either your pressure or return line pulsate?

I’m checking the fuel line routing and security this morning. After that I’ll pull the return line at the tank, stick in a gas can and see what kind of flow I’m getting.

Thanks again!

No, not that you could tell. I would think that the line pulsating would indicate the pump was cavitating. Running the return to a separate container for testing should show you something.

I think I’ve found and corrected my noisy fuel pump issue.

With the engine running I felt and tugged on the fuel lines with no change in the pump noise until I got to engine compartment. The AN 6, pressure fuel hose attached between the engine and the steel fuel line at the frame rail could be moved and the noise would stop. The line was attached in a horizontal position. I situated the hose in a more vertical position and the noise and pressure line pulsation are mostly gone. Much quieter, cant hear it driving and only faintly with the hood open.

Attached a picture of the hose in its new position.

I found with this system any restriction is going to cause these symptoms. It's a good system, just requires a lot of pre planning.

Tuts,

Thanks for your input and yes it appears these systems are pretty touchy. I learned something new today.

I was hoping for better MPG than 14 from your build. I got better than that with a leaky Rochester B carburetor on a 216 with a half a ton of fertilizer in the bed on hilly roads. I wasn't winning any races however.
Do you think that you can tweak the system to get better MPG?

You and me both Carl.

I can definitely adjust the AFRs some more. Bumping up the cruise AFR is something I might try. I’m kind of hesitant to make more adjustments as the setup I have now is working pretty well other than the mileage.

The upside to this system is that you can save the current settings, tinker with them, and always be able to come back to exactly here if you don't like the changes.

Fibonachu,

Totally agree, that is the upside to this system. Easy to do via the controller and only takes a minute.

I have my Cruise AFR set at 15.5 now. I wouldn’t think I could gain much going any higher and want to avoid getting to lean.

I’m running 215-65R16 tires that are 27” tall. Taller tires, say 30” would probably do way more toward improving the MPG.

Really am enjoying the system. Starting and throttle response are noticeably better.

What rear gear ratio are you running?

Carl,

I have 338 gears in it.

Man, I couldn't get over the hills around here in direct with that high of gears!

BC59,

I see what you mean. We don’t have that kind of terrain here, it’s pretty flat.

That looks like a fun drive.

I wouldn't recommend taller tires with those gears. If you are running a three or 4 speed with a final drive of 1 to 1, you are likely suffering from heavy lugging on the onset of every shift, followed by the need to make the engine scream before the next upshift.
Not exactly conducive to decent gas mileage. Have you considered a T-5 with overdrive? If you do, you will need to go with 3.73 or higher ratio rear gears. That setup will result in the engine remaining in the optimal RPM range for a stovebolt engine upon every shift and you won't need to make the engine scream before each upshift. That will improve your MPG.

As far as all cylinders running even A/F ratio's, I run a stand-a-lone A/F gauge on my 250 engine with a single O2s in the down pipe. I have my dual Carter W-1's set up for 15 to 16 ratio when running on level ground at 65 mph. It varies up and down but averages out around 15.5. The lower speeds always stay above 14.7, with idle at 15.5. With dual carbs placed between cylinders 2 & 3 and 4 & 5, I am getting pretty even distribution. I recently install a stock single carb intake with a stock Monojet carburetor that came off the engine when I pulled it from a yard years ago. The A/F ratio's were off the scale, 18.0 or higher, yet the truck ran fine, just as GM set it up. I tried to richen it up to get the ratio's down, but the exhaust smell was overwhelming rich. The high ratio's were due to the poor distribution, I'm sure the outers cylinders were lean and center was rich, but thats just the way they run. I would bet money, every inline has the same issues. I switched back to the dual setup, 300 mile round trip last weekend, 65 mph interstate ( fairly level both ways ) 18.5 mpg average. If it would only start like fuel injection, I would be happy.

52Carl,

With the 338 gears and 27” tires the truck doesn’t really drive much differently then it did with the 390 gears, except that I can cruise at 60 MPH at 2700 RPM. The T-5 is probably the optimal setup but I like my old three speed and would like to keep it.

Joe H is running a 308 gear set, 28” tires and no overdrive behind a 250 I6. He’s getting great mileage. He’s running dual carbs in a 37, 1/2 ton. Not exactly apples to apples but has to be in the ball park with what I’m trying to accomplish.

I haven’t decided yet but I’d sure like to try some taller tires.

My '50 3100 came with a full pressure 235, a mid sixties Saginaw 3 speed, and 3.08 rear end gears. In first gear, it could not get out of its own way on a hill, or if one rear tire was in a slight depression. It did go down the road nicely at 60+ miles an hour, but getting to that speed
with that setup involved lugging the engine in first gear and then mashing the gas until the engine was screaming right before the next shift where in again lugged. This process continued through 3rd gear.
I couldn't live like that anymore, so I went with a T-5 with .72 overdrive and a rear end out of a 2001 Nissan Xterra. That rear end is basically a Dana/spicer rear end. It was limited slip as well. The gear ratio is 4.64 to 1, which I was afraid would be too high, but with the .72 overdrive 5th gear, it worked out very well. I did go with 215/85-16 tires (30.5") in place of the stock 28" tires and that dialed everything it for me. It is an absolute dream to drive. I want to race people with it. I can pull stumps and drag them down the road at 70 miles an hour.
I have not done that yet, but I swear I am going to do that one day. I need to call the YouTube right before I do it so that they can send their camera crew out to film it. I guess that's how it works...

Have you used that RPM/tire height/rear end gear calculator to verify what your RPM is with what you have and what it will be with taller tires? Hopefully someone will come along soon and provide a link to that calculator.

RPM and MPH difference are exactly proportionate to the new tire OD / old tire OD (preferably at speed for expansion, but difficult to estimate). Remember to factor in the aspect ratio if inputting data, and use mm as needed.

The aerodynamics of an AD truck is similar to a billboard. Fighting wind resistance requires engine torque. The torque of the 235 is shown on a curve of a GM RPM/torque/HP graph. The sweet spot or power band will be between RPM points below and above the maximum torque. If you look at the graph, we can agree (to disagree) that at 1200 the engine is "getting it's legs" and after 2800 torque takes a big nosedive. The problem is that the engine(s), that provided data points for the graph, was (were) brand new. The cylinder compression is the best that it's ever going to get. The Rochester B was new and didn't have leaking problems. Fuel to air ratio was perfect for the needs of the engine testing. So, the torque or power band of today's used 235 will be less than the GM graph.

If at 65 MPH we want to speed up, do we want to press down the accelerator pedal or do we want to downshift? I for one would like some torque in reserve so I don't have to shift. This means I want to be somewhere inside the power band. Using 52Carl's setup as an example, I plugged the numbers into the calculator (http://www.wallaceracing.com/gear-speed.php). I also added 3.42 and 3.73 ratio rear axles for comparison.

I made a rough graph (questionable accuracy) for explanation purposes. The yellow is the power band. The red, blue and green represents the slope of the respective rear axle ratios. I like to look at the center of each slope, within the power band, to find the MPH below. The idea being you pick the rear axle for the highway cruising speed you want.

Buoymaker,
What was the tire size used for your graphs? I am assuming that you used a constant size for each of the three axle ratios, I am just curious what tire size you plugged in.
The handy thing about tire size options is that it allows one to dial in the final results one is shooting for by trying different tire sizes.
I went from 28" tires to 30.5" tires and experienced a significant seat of the pants difference in driveability in 1st gear. It changed from a almost useless granny gear to a very usable 1st gear.
The 30.5" tire change also reduced the RPM at highway speed (65-70 MPH) in fifth gear (.72 overdrive) to below screaming.

52Carl’s real world experience with a tire diameter change is what I’m more interested in.

Anybody out there have a Task Force truck with a 235, three speed transmission, 338 gears and 30” tires? How does the truck perform with that tall of tire? What kind of RPMs are you turning at 60 MPH on a flat road? What’s your average MPG?

Thanks in advance for any info you can offer.

The 30.5" bs. 28" change: RPM is down 8%, definitely feel different, but 3,000 only loses 250 RPM; 60 mph becomes 65.

Go to the website. You can only enter one tire size at a time (I used 30.5") but it allows you select several different rear axle ratios.

To continue on, the graph only shows final gear. You can do the same thing for the other gears (1 thru 4). This allows you to determine your shift points.
You want it such that the engine RPM doesn't drop drastically between shifts and stay in the power band if possible.

Not many transmissions have multiple choice as to internal ratios, which control RPM % change on shift.