L31 Extreme Budget Build

[GrimsterGMC]

Yeah,I'm running that rig now but I want to cut two openings in the rad. support,one either side of the rad. and run two 3" hoses to my breather. If I position them right I'll get good ram air. I've got to figure out how to baffle them so I don't get rain injection while keeping airflow.

As long as they are running uphill to the filter I don't think there will enough air velocity in the tubes to carry any water all the way up into the intake, and they will drain themselves when you slow down. That's assuming you slow down.

 

[L31MaxExpress]

If the math works out halfway decent it is getting phenominal fuel mileage cruising 65 mph. Those 29# injectors are operating in a 7-9% duty cycle range maintaining a steady speed with about 15% throttle and it is pulling about 17 in/hg manifold vacuum at 2,500 rpm cruising with the ac on at that speed on flat road. Rough math with premium fuel allegidly ~6.27 lbs per gallon, it is knocking down 22ish MPG at 8% duty cycle. Like 19.5 mpg at 9% duty cycle and 25 mpg at 7% duty cycle. Frankly considering the way I have been playing with the throttle and all in town DFW traffic driving it is sipping on fuel. Put nearly another 30 miles on it and been WOT multiple times and still showing ~1/4 tank.

At 4,800 rpm it hit 60% duty cycle today and was still a shade lean from the 12.5 commanded. That is ~310 hp worth of fuel at 0.45 bsfc and ~350 worth of fuel at 0.40 BSFC. Should fall somewhere in the middle of those values. Right in line with what the marine manufacturers claimed from their marinized versions of the L31 using the same cam.

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I adjusted the cycling switch a full turn out and the compressor stopped cycling as frequently. Its not overly hot today, but the humidity is killer. AC is holding around 35F now before it cuts the compressor off and the evaporator is dripping a lot of water now out of the drain. Did not need more than the 2nd notch on the blower to stay cool driving around today.

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This was cruising 65 mph then a 3-2 kickdown and acceleration up to ~85 mph. Pulls well on the 3-2 kickdown and that sound, lol. I figured out where the additional 2* of timing over what I was commanding for the WOT centrifical advance was coming from and for now pulled it down from 34* to 32*. Its coming from the vacuum advance function due to the manifold vacuum it is building at higher rpm. Seems happier at 34* now than it did at 36* and feels like it pulls stronger.

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[Scooterwrench]

That's assuming you slow down.

Only to put gas in it.

 

[Scooterwrench]

If the math works out halfway decent it is getting phenominal fuel mileage cruising 65 mph. Those 29# injectors are operating in a 7-9% duty cycle range maintaining a steady speed with about 15% throttle and it is pulling about 17 in/hg manifold vacuum at 2,500 rpm cruising with the ac on at that speed on flat road. Rough math with premium fuel allegidly ~6.27 lbs per gallon, it is knocking down 22ish MPG at 8% duty cycle. Like 19.5 mpg at 9% duty cycle and 25 mpg at 7% duty cycle. Frankly considering the way I have been playing with the throttle and all in town DFW traffic driving it is sipping on fuel. Put nearly another 30 miles on it and been WOT multiple times and still showing ~1/4 tank.

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I adjusted the cycling switch a full turn out and the compressor stopped cycling as frequently. Its not overly hot today, but the humidity is killer. AC is holding around 35F now before it cuts the compressor off and the evaporator is dripping a lot of water now out of the drain. Did not need more than the 2nd notch on the blower to stay cool driving around today.

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This was cruising 65 mph then a 3-2 kickdown and acceleration up to ~85 mph. Pulls well on the 3-2 kickdown and that sound, lol. I figured out where the additional 2* of timing over what I was commanding for the WOT centrifical advance was coming from and for now pulled it down from 34* to 32*. Its coming from the vacuum advance function due to the manifold vacuum it is building at higher rpm. Seems happier at 34* now than it did at 36* and feels like it pulls stronger.

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That's pretty good MPG for a wall with wheels.

 

[HotrodZ06]

I need fuel economy like that in my truck.

 

[L31MaxExpress]

I need fuel economy like that in my truck.

It definitely does not seem like it is going to be bad, especially given how much I have been playing around in it. Fun to hear it go VROOOM, lol. That was ~30 miles of playing around and some idling at traffic lights and such. I only put like 10 gallons in it to bring it up from the orange hash mark to 1/2 tank. So even jumping on it at every opportunity that presents itself probably still getting 10-12 mpg in town. When I can calm my right foot down or set the cruise on a longer trip, should do quite well. My 97 van with its 383 can easily get single digits driving it like I have this one.

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[Scooterwrench]

When I can calm my right foot down or set the cruise on a longer trip, should do quite well.

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Wish you luck with that!

 

[L31MaxExpress]

Dual 2.5" pipes actually fit well over the axle. A lot of clearence everywhere. Mandrel bent from front to rear as well now.

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[L31MaxExpress]

It did not change the sound outside much but all the difference in the world in interior cabin noise. Never have been a fan of axle dumped exhaust even under the bed of a truck. I just put those on to keep from baking the rear axle and this is now the way I wanted it. I ended up doing the 45* angle vs straight out the sides, it was easier and I do like the look as it is a bit different than how it would have come. Less interior noise at highway speeds too.

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[Scooterwrench]

It did not change the sound outside much but all the difference in the world in interior cabin noise. Never have been a fan of axle dumped exhaust even under the bed of a truck. I just put those on to keep from baking the rear axle and this is now the way I wanted it. I ended up doing the 45* angle vs straight out the sides, it was easier and I do like the look as it is a bit different than how it would have come. Less interior noise at highway speeds too.

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Sounds like my ElCamino minus the lopey idle. What was that you blew out from under the truck?