Revisiting Mercruiser Dual Plane MPFI manifold
#52
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Re: Revisiting Mercruiser Dual Plane MPFI manifold
Same lower manifold was sold formerly as the Street & Performance TPI intake. I have 2 upper plenums for that manifold. One with dual 58MM TPI like openings and a 90MM 4-bolt LS throttle body.
Last edited by Fast355; 09-02-2024 at 08:57 PM.
#53
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Re: Revisiting Mercruiser Dual Plane MPFI manifold
This is the one I have and the lid it came with that uses the 58mm TPI or LT1 style throttle body.
This is the 90mm 4-bolt syle lid for the same lower manifold. Needs a little cleanup work for the Fitech 92mm opposed to a 90mm.
I have not ruled that manifold out completely but I have not been able to find a fuel rail that matches it correctly yet.
This is the 90mm 4-bolt syle lid for the same lower manifold. Needs a little cleanup work for the Fitech 92mm opposed to a 90mm.
I have not ruled that manifold out completely but I have not been able to find a fuel rail that matches it correctly yet.
Last edited by Fast355; 09-02-2024 at 10:31 PM.
#54
Re: Revisiting Mercruiser Dual Plane MPFI manifold
I have that same intake as well with the 90mm 4-bolt LS style lid. I have messed around with injection timing changes on multiple setups. I have yet to see it make any real difference on any setup except in idle and low load, part throttle drivability. WOT it made ZERO change for me after adjusting the AFR to match what it was. I have run them with the Boundary as low as 5.5 and as high as 7.5. I have found setting for 6.5 boundary and a 6.3 Normal/Makeup warmed up has worked well on numerous setups. 6.5 boundary is BDC on the intake stroke for reference. I have used the same value as the boundary to as much as 1.0 difference in the Normal and Makeup tables. Would love to hear what the magic formula is there to gain nearly 60 ft/lbs from injection timing because I have just not even seen a 10 ft/lb difference on anything with a huge range of change in the adjustments and that was easily brought back tp the baseline value adjusting the fueling for the change that the injection timing made. Over 6.5 on the Boundary tends to cause a massive lean tip-in as well while the calculators show I should be over 7.5 with my cam profile. I am not calling you a liar by any means but I want to know how you realized those gains and take another stab at it myself if it in fact made that much of a difference. I feel like it maybe so numb to change on the setups I have tested it on because the duty cycle on the ones I have tested is fairly high, in the 60-75% range. Past 3,000-3,500 rpm the duty cycle pushes the injection timing values into the overlap period anyway. Idle and low load I have seen it shift fueling 10-15% or even more optimizing the values to deliver the target air/fuel ratio on the least amount of fuel though.
Single plane out performing the dual plane across the whole RPM range on a 350 is NOT happening. If you are starting a pull at perhaps 3,500 rpm on a healthy 383 I could see the single plane doing as you claim, lock the converter and start the pull at 1,500 rpm, not a chance in the world the single plane is doing better. I pulled a single plane off and put a dual plane in its place and instantly had a lot more torque with nothing else changed. Off-Idle to 4,000+ RPM it is a completely different engine and even flash stalls the same converter to a higher rpm. With a TH400 and a 3.08 gear the torque was a welcomed addition. I have both manifolds and have run both, not like I have a dozen of the dual plane manifolds I am trying to sell someone either. I am going to a single plane on a 383 but that is a different story entirely and for a different reason. I am purposely trying to kill off some low-midrange cylinder pressure in that setup. This is what it cranks with the other 7 plugs still in it even after removing the Rhoads V-Max lifters it had in it. The new cam going into this engine also has a later IVC. I moved from an area that had cheap, plentiful E70 testing E85 to one that 91+ is $4.00/gal. My goal is to be able to run 89 at most.
Single plane out performing the dual plane across the whole RPM range on a 350 is NOT happening. If you are starting a pull at perhaps 3,500 rpm on a healthy 383 I could see the single plane doing as you claim, lock the converter and start the pull at 1,500 rpm, not a chance in the world the single plane is doing better. I pulled a single plane off and put a dual plane in its place and instantly had a lot more torque with nothing else changed. Off-Idle to 4,000+ RPM it is a completely different engine and even flash stalls the same converter to a higher rpm. With a TH400 and a 3.08 gear the torque was a welcomed addition. I have both manifolds and have run both, not like I have a dozen of the dual plane manifolds I am trying to sell someone either. I am going to a single plane on a 383 but that is a different story entirely and for a different reason. I am purposely trying to kill off some low-midrange cylinder pressure in that setup. This is what it cranks with the other 7 plugs still in it even after removing the Rhoads V-Max lifters it had in it. The new cam going into this engine also has a later IVC. I moved from an area that had cheap, plentiful E70 testing E85 to one that 91+ is $4.00/gal. My goal is to be able to run 89 at most.
That's hilarious.
I won't even waste my time posting the printouts for each intake then.
#55
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Re: Revisiting Mercruiser Dual Plane MPFI manifold
I'm 80% tempted to test this POS iron marine "7000 RPM" intake that I have, just to show that it DOESN'T make more power and tq than all of the other, single plane LTR intakes that I've already tested. It's pretty pointless, though. We already know that the marine dual plane is perfect for it's application; a boat....anchor. OEM's didn't go through the expense, effort etc. to designing newer, single plane intakes, to lose power and tq!
#56
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Car: 1983 G20 Chevy
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Re: Revisiting Mercruiser Dual Plane MPFI manifold
Literally been stated but for some reason Tom is the one that thinks I am judging on an open differential burnout length. I have run sub 2.00s 60' times with open differential too many times to count. This was literally a 0-60 stalling against the converter a bit, do you hear me burning tires, no. It was over 1 full second quicker with the dual plane and thorley tri-ys than it was with the Projection 4150 single plane and Hooker iron manifolds. Both the headers and dual plane decreased the timed acceleration times as well. It is even quicker now that I have ditched the Proflow ECM and went to a P59 that I tuned on a speed density custom operating system. The larger 454 air cleaner and ducting I put on it stopped the intake vacuum buildup at higher rpm as well and roughly halfed the WOT vacuum I saw in this pull. That added power as well. The tuned P59 and 454 air cleaner are literally the only changes I have not had it back on the dyno for.
https://youtu.be/UjEKGehu1M8?si=aEYoM0_ZrE3dFjR6
I have also posted 2 additional dual plane MPFI manifolds dyno graphs that were also on an actual dyno and made more torque. So it is not just me or this intake that worked better.
I am still interested in how injection timing added 60+ ft/lbs when I have never seen it change power at all when the AFR was corrected after the injection timing change. I am more interested in the injection timing because I too am about to swap a single plane on my 383. Hell for science I would go back to the Proflow 4150 manifold on this and play with the injection timing on the P59 as well if it made more power than the dual plane. 60 ft/lbs is more than the dual plane gained compared to the Proflow 4150 single plane.
Last edited by Fast355; 09-03-2024 at 11:20 AM.
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