90 truck with 86-87 Corvette engine

[Supercharged111]

Right where you spend most of your time driving it.

3000?

 

[L31MaxExpress]

The TPI is only good at midrange, it sucks at everything else.

x2. TPI sucks on low-speed off-idle torque, losses everywhere under 2,600 rpm for maybe 10% gain at 3,200 where it has peak resonance, then it falls off above 4,000. A dual plane manifold has more average torque from 1,000-5,000 rpm than TPI. The torque loss cruising in overdrive at say 1,800 rpm is very evident.. Not like I did not run one for a while. TBI on even a Victor Jr Single plane had a better torque curve and was better on fuel. The one place TPI did do well was towing in 3rd gear at 75 mph. With my 3.08 gear it put me in a RPM range that it was helping build torque. Otherwise driving around and cruising at low rpm, it was pretty much a dog. There is a reason GM did not put them in trucks. Also worth mentioning a long runner LS truck manifold is also pretty much garbage for torque under 3,500 rpm compared to a dual plane as well, the long runner LS manifold is very good in the upper-midrange up to 6,200ish rpm, but a total dog down low. I wish someone offered a single 4150 throttle body flange equipped dual plane MPFI manifold for a LS. Might have made the 6.0L in my 87 G20 tolerable from a low-midrange torque perspective.

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[L31MaxExpress]

I have not thrown this out yet, but the budget L31 no longer has the Proflow 4 single plane manifold on it. I picked up another Mercruiser dual plane MPFI manifold dirt cheap and swapped it on, keeping the rest of the Proflow4 setup intact. I was even able to use the Proflow4 fuel rails, injectors and throttle body on it. Gained about 40 ft/lbs of torque at 2,500 with zero changes to the tuning. Off-idle torque is night and day better as well. I feel like the EFI manifold manufacturers are lying through their teeth about a single plane being better with a MPFI setup for a typical street engine now. They want the race look and sacrifice torque while absolutely lying about it. Edelbrock should have a 3,500-7,500 rpm range on the 4150 PF4 manifold. Mercruiser dual plane manifold builds a ton of low-midrange grunt on a mild L31 350 compared to a single plane.

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[Scooterwrench]

Ok,consider me schooled. I had the idea these intakes made good low and mid but fell off on top.

 

[Supercharged111]

Ok,consider me schooled. I had the idea these intakes made good low and mid but fell off on top.

Nope, they fall off on both ends. I suspect why they get a falsely good rap for low end torque is that the term "low end" seems to be subjective. Watch an episode of engine masters and you'll see their low end starts at 3000 RPM.

 

[L31MaxExpress]

Thought this had some interesting information in it when I saw it.

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[Scooterwrench]

Low end is idle to 2000 for me,2000-4000 mid an 4000 up for high.

 

[L31MaxExpress]

Low end is idle to 2000 for me,2000-4000 mid an 4000 up for high.

I am more in the Idle-2,500, 2,500-4,500 and 4,500-6,500 range myself. Talking low, mid, high rpm ranges. Consider most engines I build idle 750-850 rpm and spin past 6K fairly effortlessly. I tend to shift them in the 5,500 range though for longevity and seldom tap into the upper rpm potential. Fuel kill is typically 6,000-6,500 although I have had a few that twisted 7K or more. The 383 in the 97 has been 6,500 a few times, but I have it set to kill the fuel at 6K currently with a 5,500 rpm WOT upshift.

 

[Scooterwrench]

Thought this had some interesting information in it when I saw it.

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Harleys have the same problem. The rear cylinder is always richer than the front. It actually works good because the rear cyl. gets less air causing it to run hotter but gets a little more fuel which lowers combustion temp. and helps balance the temps out. When I'm setting up A/F mixture I sniff the front cyl. when I can.

 

[The_Family_Tahoe]

I have not thrown this out yet, but the budget L31 no longer has the Proflow 4 single plane manifold on it. I picked up another Mercruiser dual plane MPFI manifold dirt cheap and swapped it on, keeping the rest of the Proflow4 setup intact. I was even able to use the Proflow4 fuel rails, injectors and throttle body on it. Gained about 40 ft/lbs of torque at 2,500 with zero changes to the tuning. Off-idle torque is night and day better as well. I feel like the EFI manifold manufacturers are lying through their teeth about a single plane being better with a MPFI setup for a typical street engine now. They want the race look and sacrifice torque while absolutely lying about it. Edelbrock should have a 3,500-7,500 rpm range on the 4150 PF4 manifold. Mercruiser dual plane manifold builds a ton of low-midrange grunt on a mild L31 350 compared to a single plane.

I completely agree the aftermarket EFI manufacturers are not being honest. Dyno tests have shown repeatedly the longer runners will make more torque lower in the rpm range when tested back to back on an otherwise identical small block v8. I'd like to see an rpm air gap converted to use port injection compared with the single plane proflo type manifold. I expect the result would be similar to what your mercruiser intake is doing. I don't understand why one of the big manufacturers doesn't make a dual plane port intake for these motors.
Where did you find the mercruiser intake? I have been looking for months and haven't been able to locate one for a fair price.