Inline 6 firing order?

[David_L6]

Starting with the Mark 75, what's the firing order of the various inline 6 cylinder Mercs.?

[Raceman]

David, I can't remember what the firing order is on an inline six without going and looking, but let's see if this partially answers your question: I believe that all the inline 6's had the same order with the exception of the Twister1, Twister2, & T2X, all of which had different crankshafts.

[Mark75H]

The answer to David's question is Merc changed the firing order more than once.

The Mark 75's used 164253 and a common exhaust chamber......no dividers.

The 76 ci Merc 800 and Merc 850's begin the 145236 firing order.

It seems to me there is another firing order used on one group or another.....I think the original tuned exhaust was the top 3 and the bottom 3 as groups, rather than the every-other-one grouping used later.

[Raceman]

I'll try to look at a T2 Monday and see how they fired. I know that on the ones I've got the water jacket cover is from production engines on the ones I've checked and it's wrong for the Twister1's and foward. I don't know if they stayed that way on all of em.

[David_L6]

Curiosity about the exhaust tuning was my reason for asking about the firing order.

Did the Mark 78 have the same firing order as the Mark 75?

[David_L6]

Sam, I've got it now! (I think).

I've always raced B, C, D, E and haven't fooled with the 6 cyls. I wondered how the stacks worked on a 6, but it's the same as any other motor. #2 fires 180 degrees after #1, #4 fires 180 after #3, and #6 fires 180 after #5. Nuthin to it!
What makes the 6 cyls sound like they're turning 20,000 RPMs?

[Mark75H]

Yes, you are right about the pairs of cylinders firing alternately at 180º

[Mark75H]

I have one set of pipes that I think tells the story of why they sound twice as fast as they really are. About 2 or 3 inches from the end of the pipe the paint burns off in a nice little ring. Before that ring and after that ring the piant is ok....the pipe isn't as hot. I think the sound waves are hitting each other in the pipe and hammering very hard at that spot. That's the only way I can explain a hot spot in the middle of the pipe rather than closer to the motor.

My theory is for each exhaust opening pop there is also a pop caused by the sound waves having that collision in the pipe.

What I don't know is why the 2's and 4's don't seem to have the same effect. Same bore and stroke, same port diameter, same pipe diameter, same pipe length.

[T2x]

Sam is your 75H water injected at the stacks?

T2x

[Mark75H]

Yes. I have a windshield washer reservoir that is refilled by the motor's water pump (tiny hose). A micro switch in my Keller 200 switches off the washer pump at full throttle (learned that from an 'old' alky racer). Otherwise, I'd need a 2 gallon tank even for a short course race.

I use a toggle switch to cut the water off for starting and coming back to the pits so I don't put water in the cylinders while starting or running slow.

These pipes will burn the paint at that particular spot regardless, so the pipe being cool in front of the burn ring is not due to the water injection. Down close to the motor you can almost touch the header in the area before the water enters immediately after I come back to the pits (even if I forget to switch the water on, duh)....but don't grab those stacks!

[T2x]

On my later 1250 Stackers...we ran a switch for water injection only while planing and accelerating out of turns....earlier non water injected Stackers had nothing at low end..... I ran a single Glastron Molinari in the late 60's at a race in Maryland I think...where I averaged 80 mph into the wind and 18 mph down wind...... That's another potential entry in most embarassing moments.

That was repeated by Jimmy Caldwell (ex merc tunnel driver...later Reggie Fountain's plant manager) some years later when he built and raced a 32' offshore tunnel (scaled up Seebold design) at an event in the Hudson off the westside of Manhattan... Even with a Mercruiser Typhoon package he dropped 40 mph down wind........ then he put a pickle fork through his Suburban while putting it on the trailer.

That boat was later bought by his Reggieness...and painted his classic White, Red and Blue "Spirit of 76" colors. Sadly early Fountain purchaser (and investor I think), Skye Gillespie, was killed when the hull blew over.....no way a none experienced tunnel boat driver should have been anywhere near that thing.

T2x