D Mod ques.

[Smitty]

In the mid-'70s, there was some opinion in the D Stock classes that the Mk55 "fishing" block, with its slightly lower port-timing and the torque to pull a wheel with a bit more pitch, might be a better engine at least for short-course work, than the Mk55H block. Don't know what the final verdict was on that, but I have a Mk55 fishing block from those days, bored .015"-over but never used for anything. Since the 40" Mercs seem to have become obsolete and I assume unwanted for D Stock, I thought I might build this old motor with the exterior appearance of an old alky D powerhead, with pipes and all, but as a table lamp!!

However, I see that the 40" Mercs are legal for D Mod. I know a young fella with a boat of appropriate size for the class. What I want to know is if there's a rule I haven't spotted that makes some provision that lets the 40" Mercs run even-up with the 44s . . . . Otherwise, it would seem not worthwhile to start with anything less than a 44. Anybody??




(BTW, is the E Mod class, as it existed in the late '70s, now gone, or changed? I thought E Mod Hydro and Runabout, featuring the 44s, were the only interesting Mod classes at that time, because they had a lot more scope for actual Mod-ification than any of the other classes (which struck me as being little more than stockers with stacks.)

[fcliff]

The 40 can run at a lighter weight than the 44. Its Hydro weight is 450 instead of 470. We don't see many 40s in the 750 class but mostly because the 44s are so available. Go for it Smitty the 40 can be very fast and competitive on a good boat and on weight.

[Larry M]

In the NBRA the 40ci Merc is run with the Tohatsu in what we call the D class, it is a very even match. I am building a 40ci motor to sell right now that should be a good one. Our E class is the 44 ci Merc.
Larry Mac

[Smitty]

Thanks, Cliff. This new guy can probably come out right on weight.

[mercguy]

Thanks, Cliff. This new guy can probably come out right on weight.

do it!! We need more 750's in the Region!! We also run 850 at most races also, so he can step up and run that class also................I usually put atleast 2 (sometimes 3) of my boats in the 750 and 850 classes............

[trident]

In the mid-'70s, there was some opinion in the D Stock classes that the Mk55 "fishing" block, with its slightly lower port-timing and the torque to pull a wheel with a bit more pitch, might be a better engine at least for short-course work, than the Mk55H block. Don't know what the final verdict was on that, but I have a Mk55 fishing block from those days, bored .015"-over but never used for anything. Since the 40" Mercs seem to have become obsolete and I assume unwanted for D Stock, I thought I might build this old motor with the exterior appearance of an old alky D powerhead, with pipes and all, but as a table lamp!!

However, I see that the 40" Mercs are legal for D Mod. I know a young fella with a boat of appropriate size for the class. What I want to know is if there's a rule I haven't spotted that makes some provision that lets the 40" Mercs run even-up with the 44s . . . . Otherwise, it would seem not worthwhile to start with anything less than a 44. Anybody??




(BTW, is the E Mod class, as it existed in the late '70s, now gone, or changed? I thought E Mod Hydro and Runabout, featuring the 44s, were the only interesting Mod classes at that time, because they had a lot more scope for actual Mod-ification than any of the other classes (which struck me as being little more than stockers with stacks.)

To your point about the low port service blocks, vs. the 'real' 55H, the verdict is in, and the service blocks dominated DSH at the end of the Mk55 era.

BTW, I still have mine...

See my article on this subject, pasted in:

Mark 55 'Service Block' D Motors:

The last Mk55 Stock Outboard race motors were very interesting. Originally we had the Mark 55H and the Mark 55H-1. Those were built in 1956 and 1959 and both versions had +.060" higher intake and exhaust ports and big carbs. The first models had Carter carbs, which proved troublesome and the H-1's had Tillotson KA7A's, plus there was an update kit of KA7A's for the earlier motors. We ran those motors to death... literally.

Mercury made some replacement blocks and gearcases, and parts like pistons and rod bearings, etc. were still readily available new. Then we ran out of nice 55H blocks. An experiment was done, by individual racers, to substitute the lower ported service motor blocks for the worn out H blocks. I saw some of those tests, BITD. That block change, to what should have been a slower ported version, but combined with all the tricks we learned over the years as to what a Mk55 liked for individual parts and internal setup, gave us a motor that was, as expected, slower on top speed than a good 55H, but IT TURNED BETTER LAP TIMES AROUND THE RACE COURSE! What? 1 to 2 mph off on sheer top end, but quicker around the course? Guess who wins? Obviously the service block had a better torque curve and got to speed earlier on the straight. Oh, the service block was less fussy to prop, too.

The APBA rules were changed to allow the service blocks as replacement blocks on the Mk55H for the D classes. Now the question was which service block is best? We quickly found the later single cut 5/8" round port (think Mk35A, Merc 300) was NOT the answer. In Mod, where the ports can be significantly altered these can be made to really run, but in Stock, where the ports have to be OEM stock, the earlier double cut 9/16" port was better. OK, they made those blocks from 1955 (predating the Mk55H) through the 1958 models. 1959 was the 5/8" round ports, the Mk35A.

I was building lots of service block racing Mk 55's. I call them Mk55H-S, as in Service block, to not confuse them with the high port original H's. Some guys sell those motors to collectors as H's, but that is misrepresenting them. Dishonest or ignorant, you decide. (I've seen basically anything on a H unit called a 55H, even 44's) We would bore the service blocks, remachine the case cover for the KA carbs and build in everything we knew to make a Mk55 run. Measuring these pre-1959 blocks showed they were well made, ports were machined well within spec. I noticed certain blocks were unpainted, a very dark gray color... if you scratched it with a scriber, it was shiny aluminum. Quickly figured out these were early models, 1955 or so... Apparently something they used in manufacturing etched these early blocks that gray color, and they became known as 'black blocks'. Also noted the very earliest so-called 'black blocks' were cast differently with the sleeves actually protruding, standing proud, with no aluminum casting at the bottom end where the transfer passage starts. Later 'black blocks' have the normal casting of aluminum to the ends of the sleeves, and a blunt edge to the passage. Found those really early blocks, serial number below 89XXXX, 'black blocks', with the odd sleeves, properly built, ran like 'Jack the Bear'. ALL my best service block D's used that type block, bored oversize and built to my specs. My Merc Challenge D motor, the best 40 D I have or ever had is one of those. Its an early 1955 block with everything I know how to do that passes inspection in there...

These were the D motors we were all running when the Merc Challenge came along at the end of the Mk55 era. The 44XS was not released in time for the first year of the Challenge, so Mercury made the black Challenge wraparounds with current graphics and paid us good contingency money to paint our D motors Phantom Black and run them fully cowled with that wraparound. Mine were already black. I just had to paint my silver towers black and switch wraparounds. Next year, 1987, the 44XS was introduced. End of an era. The 55's had a good run, 1956 thru 1986. Its still one of my favorite motors... I first drove one in 1960 and was instantly in love. Looking back now, as I raced both, I think the Mk55 was the better motor. Yes, the 44XS IS faster, but the Mk 55H was a better driving motor, IMHO. Sounds better, too.

Funny story, very early '80's I got a bright idea to try a true +.060" ported 55H block, on our newest pickle fork hydros, with the new three blade props, running tucked, high on the transom... Put the best parts I could find in there with four new selected, matched pistons and fresh bores... Oh, that motor ran big test numbers, but it never won a race the whole season. I dropped that entire crank train into a freshly bored and prepped early numbers 'black block' service block and went right back to winning races.

Disappointing experiment, but point proven!



BTW, for a 40 Mod, I would recommend you use the Mk35A / Merc 300 style block with the 5/8" round cut ports, as in Mod you can fix the porting deficiency those blocks had as stock motors. My best 40 Mods were built using those later blocks.

Hope this helps.

[Smitty]

Great article, Trident. I remember hearing something about the "black blocks." Have to look at mine for numbers and ports and sleeves; I shot a coat of Ford Engine Blue on it, way back when. But why would the Merc 300 blocks be better for D Mod, if you can port either block? AND (minor point!!) is Wiseco or anybody making new pistons for these old 15/20/30/40" Mercs (in +.015")??

Darneille, I was trying to find last year's Reg. 10 class participation figures. Are C Mod and D Mod about equally active? Do they have to run together to get enough boats on the course? And does a good 30" Merc four-cylinder run even-up with the good Yamatos nationally? I ask because there is a second novice to whom I am giving preliminary advice (to be corrected as he gets to some early races and talks with today's racers), and he has a boat that is slightly smaller and lighter than the first novice I mentioned above. He could go either C or D Mod (and I'm hoping he will run 125ccH as well).

[DeanFHobart]

In Region 10 the C Mods have enough to run alone. The D and E Mods usually run together to make a class.

I would suggest Not to have a Novice run either a D Mod or 125, because they run over 80 mph. That is too fast for a Novice in my opinion.

[Smitty]

Thanks, Dean. I take your point, but neither of these guys is an inexperienced teenager like I was when I started in B Stock; both are older and have experience with very fast motorized equipment of other kinds, so I'm guessing they will adapt to this in short order. But I will pass along what you say, and emphasize your knowledge level.

[mercguy]

[QUOTE=Smitty;n453947]Great article, Trident. I remember hearing something about the "black blocks." Have to look at mine for numbers and ports and sleeves; I shot a coat of Ford Engine Blue on it, way back when. But why would the Merc 300 blocks be better for D Mod, if you can port either block? AND (minor point!!) is Wiseco or anybody making new pistons for these old 15/20/30/40" Mercs (in +.015")??

Darneille, I was trying to find last year's Reg. 10 class participation figures. Are C Mod and D Mod about equally active? Do they have to run together to get enough boats on the course? And does a good 30" Merc four-cylinder run even-up with the good Yamatos nationally? I ask because there is a second novice to whom I am giving preliminary advice (to be corrected as he gets to some early races and talks with today's racers), and he has a boat that is slightly smaller and lighter than the first novice I mentioned above. He could go either C or D Mod (and I'm hoping he will run 125ccH as well).[/QUO






Cmod (500ccmh) and Dmod (750ccmh) do not run together, they have enough for their own class...........sometime we combine 750 with 850, when there are not enough 750's to have a stand alone class, but those racers (750 or 850) always have a class to race at each event. And a good Merc C will run with the yamato guys on a bigger course ( I have one in the works myself)........

BTW, I am NOT Darneille (Larry Darneille), he is the one that builds most of my boats.............I am Daren.........also the 750/850 class rep and Mod Commissioner........

and as Dean mentioned, in 750, we easily run in the 80's.........

[trident]

Great article, Trident. I remember hearing something about the "black blocks." Have to look at mine for numbers and ports and sleeves; I shot a coat of Ford Engine Blue on it, way back when. But why would the Merc 300 blocks be better for D Mod, if you can port either block? AND (minor point!!) is Wiseco or anybody making new pistons for these old 15/20/30/40" Mercs (in +.015")??

Darneille, I was trying to find last year's Reg. 10 class participation figures. Are C Mod and D Mod about equally active? Do they have to run together to get enough boats on the course? And does a good 30" Merc four-cylinder run even-up with the good Yamatos nationally? I ask because there is a second novice to whom I am giving preliminary advice (to be corrected as he gets to some early races and talks with today's racers), and he has a boat that is slightly smaller and lighter than the first novice I mentioned above. He could go either C or D Mod (and I'm hoping he will run 125ccH as well).

Why the 5/8"? Because the port centers are spaced wider and you can make a bigger center port...

[Smitty]

Thanks, fellas (and sorry, Daren), but again what about pistons/rings?

[mercguy]

[QUOTE=Smitty;n453971]Thanks, fellas (and sorry, Daren), but again what about pistons/rings?[/QU

no aftermarket pistons available that I am aware of for the 30/40 cube Mercs.............

any questions, fee free to email me at mercguy63@comcast.net

I have (4) 44 powerheads in my shop right now undergoing builds...

[DeanFHobart]

Thanks, Dean. I take your point, but neither of these guys is an inexperienced teenager like I was when I started in B Stock; both are older and have experience with very fast motorized equipment of other kinds, so I'm guessing they will adapt to this in short order. But I will pass along what you say, and emphasize your knowledge level.

Phil,

I know what you are saying. However, "experience with very fast motorized equipment of other kinds" is not boat racing. Fast boats are different than tires on asphalt.... if that is what they drove before. Make sure they have lots of seat time.

Best Regards,

Dean............

[HydroKyle93R]

Go testing. Early and often.