Nah, i didn't edit that one other than adding the #1.5 .

Past week or two, if you quote someone, your post will go over the post you quoted.

A lot of us are feeling like we have some special form of ESP. No one's won the lottery yet, so it must be the site is F*ked up.

Yah, it's a pain the azz.

We dyno tested a Dart 4150 single plane against a Performer RPM on a 516 inch big block motor. The single plane only beat the RPM by 5 horsepower, 604 vs. 599.

I'll throw in my .02.

I've run both the RPM Air Gap and a Victor Jr on a .030 over 454, 9.3:1 CR, Isky cam (221/232 @/.050, 114 LSA) ported 781 heads with 2.19/1.88 valves, HP500 800 cfm carb. So, a pretty mild build. No dyno results, only in the boat.

The RPM air gap did perform well, but fuel distribution at high rpm sucked. Spacers only made it worse. Tune for good AFR on both banks at 3500 and at 5000 rpm they were 1 full point apart (12's vs 11's for example). Distribution was not only a problem with AFR, tune for 12.6 @ 5000 rpm and # 2 and #5 were showing lean on the plugs. Jet to get all the plugs looking good, and I was in the high 11's on AFR again. Costing me power and money.

Changed to a Victor Jr this August. Of course, had to re-tune, started with HP500 jetting and leaned out from here. Tuned for 12.8 at WOT and all plugs looked good; both banks were close on AFR (no more than .2 apart). Tuned for mid-range, AFR and plugs still looked good. Picked up a couple of mph on the top end (due to the more consistent cylinder to cylinder mixture IMO). Noticed no issues on the low end - idle, planing time and throttle response all great.

Do I think the air gap is a bad manifold? No, I've used them on the street several times. However, based on my experience I'll stick to a good single plane on BB marine engines - the 15 or so foot pounds you lose at 2500 won't be noticed.

Think I have posted this before. I had a base 454 315/330 HP with a Performer RPM otherwise stock peanut port heads. Purchased a set of Performer RPM roval heads.
Had to pocket port them a bit to acheave Edelbrocks advertized air flow. Installed them and topped it off with the Performer RPM and took the boat out couldnt feel any real differance compaired to the original engine. At the same time tried 3 different marine carbs,an 830,750 and an 850 marine holleys. The carbs showed no differance in performance.
Then swapped out the RPM for a Air Gap. Had to modify a 80.00 upper coolant hose due the the hight of the water crossover. The intake cost 100.00 over the RPM. Took the boat out again and along with testing the three carbs again couldnt feel any differance between the AIR Gap and the RPM other than it cost me 180.00 over the RPM including modifying the hose. Ouch in the wallet
Next installed a Torker II didnt need the modified hose. The bow rise encountered with the above configurations was gone the boat jumped out of the water no noticable bow rise, jumped out of the water like a frog and up on plane (before had to stand up to see over the bow most of the time) and hit 75 (redline). It was like I added 70HP or better. Tested with the 3 carbs also which made no differance on the Torker. Wish I HAD GOTTEN THE CHANCE TO reprop to see just how much speed I WOULD HAVE PICKED UP. The way the boat reacted with the torker and RPM heads guessing at least 5MPH

Worried about heating of the under side of the intake THIS YEAR ON MY TOW VIHICLE COATED THE UNDER SIDE OF THE INTAKE with a ceramic coating

Did you stay with the HP500-style staggered jetting? Your results kind of make me wonder if I should be going with staggered jetting on my 489 - running 265 AFR's, Dart oval port intake and Holley 800 (HP500) carb with Lightning headers. Very similar cam specs - was that flat tappet or hyd roller?

Yes, I still have staggered jetting, but not just like the HP500. Cam is a flat tappet grind, 221/232 @.050, 114 LSA, 114 ICL, .542/.565 lift. I have the 496 exhaust modified per comments here by Raylar, which is working well for me.

Here is where I am now on jetting (note that I changed the air bleed and idle feed restriction sizes to flatten out the mixture and eliminate rich conditions down low). P is primary, S is secondary


Secondary Constant Idle Feed 0.031
Idle Air Bleed 0.07P 0.032S
Main Air Bleed 0.020P 0.018S
Idle Feed Restriction 0.033P 0.04S
Pwr Valve Channel Restr 0.069
Main Jet (P) 79
Main Jet (S) 89 Port/ 88 Stbd
Pwr Valve 8.5

It required some major changes over the HP500 stock - for example the primary idle feed restriction started at .058, I took it down to .033 to get idle transition mixture into the high 11's / low 12's

I have the Eddy Oval RPM heads (ported) with the Q-Jet dual plane performer intake on 9.6:1 CR, and didn't really think that manifold was doing it justice. Thanks for the info.

i HAVE DONE SOME FLOW TESTING OF INTAKES BOLTED TO HEADS mostly small block Fords AND cHEVYS. What I found is the performer style intakes flow about the same as factory stuff. RPM style intakes a bit more. The torker II and VrJR about the same but a bigger jump than between the Performer and RPM. aLSO FOUND BETTER FLOWING HEADS DONT INCREASE air flow of an intake.

Are you saying a stock 330/454 gained lowend with a torker manifold oval heads and no Cam?

I love reading these posts debating what type of intake to use on a BBC marine performance motor. Most have never had their motor on a dyno, let alone had their manifold on a flow bench (fixtured to the head that they are using on the motor). Here is a big taste of reality. Mercury engineering has forgotten more that most posters here (me included) on this thread when it comes to marine performance motors. The most widely acclaimed, most reliable, solid performing marine racing and performance built motor---------The Mercury HP500. After all of their testing, the Dart single plane manifold was the manifold of choice. Possible that Mercury had Dart make a special (beyond the nice blue paint) manifold with alterations to the Dart specs for the Mercury part, but it's DNA is still Dart. Still don't believe me. Ask a professional. Wilson Manifolds has possibly the most experience in cast aluminum manifolds then most. For a performance marine BBC motor, it is certainly not a dual plane anything!