"Stock" Mac 21 versus a Modded Mac 21

[dwb2620]

What is the difference between a "stock" Mac 21 versus a modded Mac 21? Or a Mac 45 for that matter. What is being done to make it modified? I thought that MACs were already hopped up from the factory.

The reason I am asking is because I keep coming across threads that talk about "my boat with a modified Mac 21" does 900 MPH or whatever with a badmamajammer prop.

David

 

[tnrcboatracer]

Many of the MAC's are modded by modifying the drum or port timing, as well as the exterior of the sleeve for port flow. It's more of a personal preference. It's also a good way to trash a perfectly good motor.

It also depends on which generation MAC you have, as filling the drum on the non-ramped drums it usually a good thing. Also filling the xfer port channels on the late model 67/84 cases is also good for torque. (lets you pull that badmamajama prop on your 28lb scale boat from a dead stop .....LOL). As with everything, the mods depend on your application.

 

[Buckshot]

What is the difference between a "stock" Mac 21 versus a modded Mac 21? Or a Mac 45 for that matter. What is being done to make it modified? I thought that MACs were already hopped up from the factory.The reason I am asking is because I keep coming across threads that talk about "my boat with a modified Mac 21" does 900 MPH or whatever with a badmamajammer prop.

David

David,

Most of the MAC .21 motors you saw me run last year where pretty much stock and as you could tell they where not hurting for power or speed. The only things really done to them was I opened up the spray bar I.D., set the head clearance, knocked the burs off of the ports and fired that booger up. I did do a little work on the outside of one of the sleeves in the hydro but it didn't relly make a hill of beans that I could tell.

No comment on the MAC .45

Might stop by the race next week and see ya.

-Buck-

 

[FloridaScaleBoater]

Jon

Can you expand on this

"Also filling the xfer port channels on the late model 67/84 cases is also good for torque. "

Have a gent down here in Florida (Bill Gibson) that is dealing with this very problem in a scale.

Says his throttle is like a light switch, it's either on, or it's off, once it's off, it doesn't like to come back on

If Bill happens to miss this dicussion I'll fill him in.

dwb2620, Sorry for hijacking your thread, would you like us to move this elsewhere?

 

[tnrcboatracer]

JonCan you expand on this

"Also filling the xfer port channels on the late model 67/84 cases is also good for torque. "

Have a gent down here in Florida (Bill Gibson) that is dealing with this very problem in a scale.

Says his throttle is like a light switch, it's either on, or it's off, once it's off, it doesn't like to come back on

If Bill happens to miss this dicussion I'll fill him in.

dwb2620, Sorry for hijacking your thread, would you like us to move this elsewhere?

PM sent

 

[Blue Print]

Hi Jon, can you send me a PM on this as well

Thanks in Advance

Merv

NZ

 

[Scott Schneider]

While I have not raced the .21 Macs for a couple of years now (Actually NO nitro engines) I did tweak on Mac .21's quite a bit.

Putting an intake plug/ramp into the rotor stuffed the case volume up a tad, Profiling the liner around the transfer windows aiding in more accurate out flow control. I was never one to try and really load up the macs like so many others did with super low squish clearance, short pipes and high nitro

Kept 45% in it, Put a 2* angle on the inner 40% of the squish band of head. With a pipe of correct volume and length set for the prop loading would spool em up to 29-31K. The modified head profile really saved plugs and engine seldom if ever would frost up the plugs or combustion chamber.

Was very common to race an entire day on a single Mc coy 9 tossing it into a box of plugs to use as testers another day.

So WHAT was the gain ? .... far greater reliability and a very stable needle, Excellent service life from the engine !!

JMO,

Scott

 

[dwb2620]

What is the difference between a "stock" Mac 21 versus a modded Mac 21? Or a Mac 45 for that matter. What is being done to make it modified? I thought that MACs were already hopped up from the factory.The reason I am asking is because I keep coming across threads that talk about "my boat with a modified Mac 21" does 900 MPH or whatever with a badmamajammer prop.

David

David,

Most of the MAC .21 motors you saw me run last year where pretty much stock and as you could tell they where not hurting for power or speed. The only things really done to them was I opened up the spray bar I.D., set the head clearance, knocked the burs off of the ports and fired that booger up. I did do a little work on the outside of one of the sleeves in the hydro but it didn't relly make a hill of beans that I could tell.

No comment on the MAC .45

Might stop by the race next week and see ya.

-Buck-

Hey Buckshot, what's up!

I'll be at the race, but I won't be racing, just helping out and watching. None of the nitro classes made, and my Whiplash GV isn't ready yet. It going to be mostly a Gas race. Even FE is gonna have 4 or 5 classes made. I entered 20 and 40 hydro, and Sport 40. Only 20 hydro had three entries. Needed 2 more to make the class. But it didn't happen. :angry: So I am just little bit disappointed as far as that goes.

David

 

[dwb2620]

JonCan you expand on this

"Also filling the xfer port channels on the late model 67/84 cases is also good for torque. "

Have a gent down here in Florida (Bill Gibson) that is dealing with this very problem in a scale.

Says his throttle is like a light switch, it's either on, or it's off, once it's off, it doesn't like to come back on

If Bill happens to miss this dicussion I'll fill him in.

dwb2620, Sorry for hijacking your thread, would you like us to move this elsewhere?

Rick,

It's cool. I do the same thing sometimes. I would like to know, too.

David

 

[Buckshot]

What is the difference between a "stock" Mac 21 versus a modded Mac 21? Or a Mac 45 for that matter. What is being done to make it modified? I thought that MACs were already hopped up from the factory.The reason I am asking is because I keep coming across threads that talk about "my boat with a modified Mac 21" does 900 MPH or whatever with a badmamajammer prop.

David

David,

Most of the MAC .21 motors you saw me run last year where pretty much stock and as you could tell they where not hurting for power or speed. The only things really done to them was I opened up the spray bar I.D., set the head clearance, knocked the burs off of the ports and fired that booger up. I did do a little work on the outside of one of the sleeves in the hydro but it didn't relly make a hill of beans that I could tell.

No comment on the MAC .45

Might stop by the race next week and see ya.

-Buck-

Hey Buckshot, what's up!

I'll be at the race, but I won't be racing, just helping out and watching. None of the nitro classes made, and my Whiplash GV isn't ready yet. It going to be mostly a Gas race. Even FE is gonna have 4 or 5 classes made. I entered 20 and 40 hydro, and Sport 40. Only 20 hydro had three entries. Needed 2 more to make the class. But it didn't happen. :angry: So I am just little bit disappointed as far as that goes.

David

I understand your pain brother! The last two years I was in TX most of my running was at our pond with Mr. Whitmire trying new things with a few events in Houston that seemed like the nitro guys were more of a bother than welcomed.

If I can help you out let me know. I'll see ya next weekend.

-Buck-

 

[Marty Davis]

Mac21's are all that I run in my Hydros now.

As for mods:

I set trapped compression ratio at 10.25:1 and head clearance at .006"

I choose a liner with timing that gives me 30 degrees of blow down time. (185 exhaust - 125 intakes = 60/2 = 30 degrees).

I like the Brad Christy Pistons as a replacement for the Mac Piston (too soft a material to have seal last very long). Brad's pistons are very hard and last and last after being broken in.

That's it.....

 

[BDM Racing]

What is the difference between a "stock" Mac 21 versus a modded Mac 21? Or a Mac 45 for that matter. What is being done to make it modified? I thought that MACs were already hopped up from the factory.The reason I am asking is because I keep coming across threads that talk about "my boat with a modified Mac 21" does 900 MPH or whatever with a badmamajammer prop.

David

David,

Most of the MAC .21 motors you saw me run last year where pretty much stock and as you could tell they where not hurting for power or speed. The only things really done to them was I opened up the spray bar I.D., set the head clearance, knocked the burs off of the ports and fired that booger up. I did do a little work on the outside of one of the sleeves in the hydro but it didn't relly make a hill of beans that I could tell.

No comment on the MAC .45

Might stop by the race next week and see ya.

-Buck-

Hey Buckshot, what's up!

I'll be at the race, but I won't be racing, just helping out and watching. None of the nitro classes made, and my Whiplash GV isn't ready yet. It going to be mostly a Gas race. Even FE is gonna have 4 or 5 classes made. I entered 20 and 40 hydro, and Sport 40. Only 20 hydro had three entries. Needed 2 more to make the class. But it didn't happen. :angry: So I am just little bit disappointed as far as that goes.

David

David,

Dont know last time you talked to Eric there, he got 4 20 hydros entered, he asked me if i cared to run my 20 mono with the hydros ,just to make the class. I agreed and will be there. No other monos entered so this way at least the class can run.

Bob M.

 

[Marty Davis]

Mac21's are all that I run in my Hydros now.
As for mods:

I set trapped compression ratio at 10.25:1 and head clearance at .006"

I choose a liner with timing that gives me 30 degrees of blow down time. (185 exhaust - 125 intakes = 60/2 = 30 degrees).

I like the Brad Christy Pistons as a replacement for the Mac Piston (too soft a material to have seal last very long). Brad's pistons are very hard and last and last after being broken in.

That's it.....

I might also ad that running high compression and high nitro, I am harder on parts than most. I try to squeeze as much out of my .21 engines as they can deliver. Probably the reason that I don't get long life out of pistons, head buttons and liners. I just keep replacing the liner,pistons,heads buttons as they give up or become highly detonated. I guess it is a little like the "Top Fuelers" in the amount of parts that you are willing to go through in order to make a lot of HP. For me, I am more than willing..... B)

 

[dwb2620]

What is the difference between a "stock" Mac 21 versus a modded Mac 21? Or a Mac 45 for that matter. What is being done to make it modified? I thought that MACs were already hopped up from the factory.The reason I am asking is because I keep coming across threads that talk about "my boat with a modified Mac 21" does 900 MPH or whatever with a badmamajammer prop.

David

David,

Most of the MAC .21 motors you saw me run last year where pretty much stock and as you could tell they where not hurting for power or speed. The only things really done to them was I opened up the spray bar I.D., set the head clearance, knocked the burs off of the ports and fired that booger up. I did do a little work on the outside of one of the sleeves in the hydro but it didn't relly make a hill of beans that I could tell.

No comment on the MAC .45

Might stop by the race next week and see ya.

-Buck-

Hey Buckshot, what's up!

I'll be at the race, but I won't be racing, just helping out and watching. None of the nitro classes made, and my Whiplash GV isn't ready yet. It going to be mostly a Gas race. Even FE is gonna have 4 or 5 classes made. I entered 20 and 40 hydro, and Sport 40. Only 20 hydro had three entries. Needed 2 more to make the class. But it didn't happen. :angry: So I am just little bit disappointed as far as that goes.

David

David,

Dont know last time you talked to Eric there, he got 4 20 hydros entered, he asked me if i cared to run my 20 mono with the hydros ,just to make the class. I agreed and will be there. No other monos entered so this way at least the class can run.

Bob M.

Bob, I appreciate your entry into the class, so it could make.

A big thanks!

David

 

[dwb2620]

Mac21's are all that I run in my Hydros now.
As for mods:

I set trapped compression ratio at 10.25:1 and head clearance at .006"

I choose a liner with timing that gives me 30 degrees of blow down time. (185 exhaust - 125 intakes = 60/2 = 30 degrees).

I like the Brad Christy Pistons as a replacement for the Mac Piston (too soft a material to have seal last very long). Brad's pistons are very hard and last and last after being broken in.

That's it.....

I might also ad that running high compression and high nitro, I am harder on parts than most. I try to squeeze as much out of my .21 engines as they can deliver. Probably the reason that I don't get long life out of pistons, head buttons and liners. I just keep replacing the liner,pistons,heads buttons as they give up or become highly detonated. I guess it is a little like the "Top Fuelers" in the amount of parts that you are willing to go through in order to make a lot of HP. For me, I am more than willing..... B)

Marty,

Thanks for the info!

David