Mercury in line 6 hop ups

[Mark75H]

All out race motors were over 200hp, I'll try to find the thread. With different port mods etc , single ring, lots of compression, they spin and make lots of power.

The 6 carb motor with 3+3 exhaust tuning crank and finger ports was "capable" of 200+ The compression wasn't raised, and the rpm was only something a little over 7,000.

The 'customer' version of this motor was only a hair over 185.

[FMP]

I might be mistaken but I'll post it. These had more compression, I'll find it. 7000+ isn't too bad.

[Mark75H]

So what is actually holding the engine back? Is it the Cross flow design?

Yes

[Mark75H]

I might be mistaken but I'll post it. These had more compression, I'll find it. 7000+ isn't too bad.

The exhaust tuning increased the running cylinder pressure and torque rather than having smaller combustion chambers.

[FMP]

Oh yes that's true.

[Dave S]

I think........ I drink...... The piston top is the limit in the L6,,,,, revrrrrude had .25 of comp gas in chamber........merc .75 on the other side of melted piston.It is all good till ya hit the limit.

[Dave S]

I like Merc ...... but v4 is the way to go. no crank flex.....better piston rod ratios.....better head /squish chamber.....merc tiwisty crank.... hot melted piston....

[powerabout]

I like Merc ...... but v4 is the way to go. no crank flex.....better piston rod ratios.....better head /squish chamber.....merc tiwisty crank.... hot melted piston....

But more pistons will make more power.
Imagine trying to get an omc 2.0 V4 wellover 200 to match a merc 2.0 v6

[mrcrsr]

The whole idea of doing this is the vintage in line 6 deal, if it came down to putting a rude V4 on the boat I might as well put a v6 on it! What are the rpm limitations of the inline? My understanding is that the later in line came with cracked cap rods like the v6

[delawarerick]

But more pistons will make more power.
Imagine trying to get an omc 2.0 V4 wellover 200 to match a merc 2.0 v6

A die hard omc guy might debate that one. I have seen some real strong 2.0 rudes and on the other hand have seen many 2.0 mercs.

[Raceman]

Prior to the introduction of the Merc V6 I was running some 1500J (same powerhead as 1500XS but without low water pickups) and Twister 2 stuff on a 15 Allison. I decided to send a 1500J powerhead to Orville Christner at Quincey Welding who had a legendary reputation in racing outboards INCLUDING building the inline 6 looper, pretty much from scratch. I got the powerhead back disassembled and the machine work was absolute art. The exhaust ports were re shaped and there was some work on the transfers on both ends. He had re shaped the windows in the pistons, which were 2 rings from an 850 and had completely re worked a new set of reed blocks, putting them in an end mill to open up the area in the middle, re shaping the rear of the holes and also re shaped the front half of the block behind the carbs. There was some work on the inner exhaust plates and other machine work that I can't remember over 40 years later. I was in awe over the quality and detail of the work. There was just one problem........................ It didn't put any speed on the boat. Somebody asked above, what was the restriction in the 1500's? It's a combination of the inefficient combustion chamber design with the deflector piston, the crossflow design itself and the way the reed blocks are configured. I've NEVER SEEN a 1500XS improved with internal modifications, but have seem many hurt by people that just can't accept the fact that they're not likely to help one by getting inside with the carbide bits. It's also worth mentioning that the factory port specs, as far as exhaust port height and transfer port height are the same between the 1500XS, the 650XS and the T2. Sam Cullis sent me the tech sheet that APBA used about 25 years ago and I still have it somewhere.

One other thing that the discussion on align boring to move crank up and raise compression fails to mention is that if you move the crank up in the block .010, you just lowered the port timing .010 at the same time. Would moving the crank that .010 and then raising the port timing .020 for a net gain of .010 help performance? I doubt it seriously but don't know for sure. What I do know for absolute certain is if you raise the port timing .020 on a standard XS you'll hurt the power from the bottom of the RPM range all the way to the top.

I've always said there's a lot more potential for hurt than there is for help in screwing with an inline 6 powerhead and if somebody's not happy with the output they'd be much better off to start with a Merc V6, all of which are loopers with a lot more potential for modification.

Jeff Griggs in S.C. who's a Formula V world Champ with tons of inline experience has said that even the 1500XS's in the last year or two have the low dome pistons from the factory. I presently have 14 1500XS's in various forms, from running to totally scattered, and haven't personally seen one with the low domes BUT I haven't measured most of mine either. Although I haven't bought any pistons for 2 or 3 years now, the last set I bought were 1500 high domes with 3 rings and were still available after market. Something makes me think the 2 rings from the 850 were no longer available in high dome. I think it's pretty safe to say that the extra tad of compression is more about acceleration than top end numbers and even there the difference is negligible.

[powerabout]

A die hard omc guy might debate that one. I have seen some real strong 2.0 rudes and on the other hand have seen many 2.0 mercs.

Yes but i think f1 2.0 merc was close to 300
Maybe a v4 could get there with an x front or newer etec front
Cant wait for someone to try.
Like to try myself but without punching through the block could be a tall order

[powerabout]

Prior to the introduction of the Merc V6 I was running some 1500J (same powerhead as 1500XS but without low water pickups) and Twister 2 stuff on a 15 Allison. I decided to send a 1500J powerhead to Orville Christner at Quincey Welding who had a legendary reputation in racing outboards INCLUDING building the inline 6 looper, pretty much from scratch. I got the powerhead back disassembled and the machine work was absolute art. The exhaust ports were re shaped and there was some work on the transfers on both ends. He had re shaped the windows in the pistons, which were 2 rings from an 850 and had completely re worked a new set of reed blocks, putting them in an end mill to open up the area in the middle, re shaping the rear of the holes and also re shaped the front half of the block behind the carbs. There was some work on the inner exhaust plates and other machine work that I can't remember over 40 years later. I was in awe over the quality and detail of the work. There was just one problem........................ It didn't put any speed on the boat. Somebody asked above, what was the restriction in the 1500's? It's a combination of the inefficient combustion chamber design with the deflector piston, the crossflow design itself and the way the reed blocks are configured. I've NEVER SEEN a 1500XS improved with internal modifications, but have seem many hurt by people that just can't accept the fact that they're not likely to help one by getting inside with the carbide bits. It's also worth mentioning that the factory port specs, as far as exhaust port height and transfer port height are the same between the 1500XS, the 650XS and the T2. Sam Cullis sent me the tech sheet that APBA used about 25 years ago and I still have it somewhere.

One other thing that the discussion on align boring to move crank up and raise compression fails to mention is that if you move the crank up in the block .010, you just lowered the port timing .010 at the same time. Would moving the crank that .010 and then raising the port timing .020 for a net gain of .010 help performance? I doubt it seriously but don't know for sure. What I do know for absolute certain is if you raise the port timing .020 on a standard XS you'll hurt the power from the bottom of the RPM range all the way to the top.

I've always said there's a lot more potential for hurt than there is for help in screwing with an inline 6 powerhead and if somebody's not happy with the output they'd be much better off to start with a Merc V6, all of which are loopers with a lot more potential for modification.

Jeff Griggs in S.C. who's a Formula V world Champ with tons of inline experience has said that even the 1500XS's in the last year or two have the low dome pistons from the factory. I presently have 14 1500XS's in various forms, from running to totally scattered, and haven't personally seen one with the low domes BUT I haven't measured most of mine either. Although I haven't bought any pistons for 2 or 3 years now, the last set I bought were 1500 high domes with 3 rings and were still available after market. Something makes me think the 2 rings from the 850 were no longer available in high dome. I think it's pretty safe to say that the extra tad of compression is more about acceleration than top end numbers and even there the difference is negligible.

I think the t2 Straight in front made all the difference.
And yes you need race pistons with rings that are half the width of stock merc ones and 2 rings max

[FMP]

I mentioned adjust ports on #45 for centreline move. Assuming everyone understood raise. The 650 is a triple I believe, the 1500 is crank spaced as two functioning triples I believe, hence same height assuming near same displacement and chest spacing. If chest spacing between tuned pairs is greater on the 6 and maintains 120 pin spacing between tuned pairs ex ports should be able to be raised to take advantage of the delayed tuned pulse from the greater travel distance. The 650 chest spacing if less should produce a higher power band or weaker low rpm.
Then the big difference in distance from top to tuner end for scavenging, more variables.

[W2F a V-King]

I like Merc ...... but v4 is the way to go. no crank flex.....better piston rod ratios.....better head /squish chamber.....merc tiwisty crank.... hot melted piston....

Maybe so.... BUT !!! the Merc has the look and the sound

What looks better on the transom ?? 1500XS or .....


I know looks don't win races....