Visit The Dirt Forum for More Information

Author Topic:   DUI or MSD...locked or unlocked
dluna
Dirt Freak

Total posts: 334
posted October 06, 2005 07:59 AM  
I am currently using a DUI distributor. I see a lot of racers using MSD ignition. I will be steping up my Mod engine program a little either next year or the year after. Do I need to switch to an MSD ignition? Will MSD give me a better spark than my DUI? If I did switch to MSD, would I have to purchase a different distrubutor?

Also wondering if I should lock my DUI distributor during the off season. Will the engine run a little rough at idle with a locked distributor? What are the pros and cons of locking the distributor? Will it make a difference if I'm using DUI or MSD? I don't currently have to crank the motor before turning the ignition on, but have read that you have to do that if you lock your distributor.

Thanks!

zeroracing
Dirt Forum Champ
Total posts: 1876
posted October 06, 2005 08:55 AM  
I run the DUI and have spun the motor up to 8900 without problems from it. But I have woundered sometimes about an MSD. But like another racer that runs one told me they are alot easier to fix problems then chasing all over the car with an msd.
Also more and more cars I see switch over to the DUI style. DUI is just more compact, and less to deal with. I am not sure actual performance number differences between the two though, I am sure both claim to be better but independent test I dont know.

leapinlizard
Dirt Freak

Total posts: 402
posted October 06, 2005 10:08 AM  
I've run both, had zero problems with either. As far as troubleshooting goes. If you learn the systems, you won't be chasing problems for long with either system. I like my MSD, but I ain't got one bad thing to say about DUI either.

dirtbuster
Dirt Forum Champ
Total posts: 2007
posted October 06, 2005 11:16 AM  
Never ran a DUI so i wont comment on it, Have always ran MSd and never had a single problem with it.

As for locked or unlocked timing. i would lock it out. Takes care of one more thing that could go wrong. and whatever you set the timing at thats what it stays at, you dont have to worry about it bouncing around depending on how the advanve mechanism is setup. It actually will prob run a little smoother at idle with all the advance in it, might be harder to start, but if you have it wired right you can spin the engine over before hitting hte ignition button and it will fire right off.

dluna
Dirt Freak

Total posts: 334
posted October 06, 2005 03:32 PM  
thanks guys.

I'll show my little knowledge of the ignition system here...
Sometimes I've wondered about the way I'm setting the timing. I run the engine up to 4K rpms or so and set it at the desired number. If I end up at 7500 rpms at the end of the straight without a locked distributor, how can I be sure it is still at 34 degrees? I assume nobody revs their motor up to 7500 without a load to set their timing.

Once I lock it out, then if I check the timing at 2K, 4K, 6K, or 8K...it should always be 34. is that right?

[This message has been edited by dluna (edited October 06, 2005).]

psycho47
Dirt Full Roller

Total posts: 48
posted October 06, 2005 03:34 PM  
Have always run a locked ditributor and had no problems. You can buy the locking plate or take it apart and have it welded. Have also always run an MSD box and had one failure.

James Ott
Dirt Maniac

Total posts: 131
posted October 06, 2005 05:15 PM  
With the vacuum advanced removed from the distributor RPM is just that. The distributor does not sense load. If you leave it as stock you can recurve the distributor to dial in the curve where you want it. When your faced with limited traction conditions rolling the advance on might not hurt. my 2cents

dirtbuster
Dirt Forum Champ
Total posts: 2007
posted October 07, 2005 05:46 AM  
we are talking mechanical advance here, not just vacuum advance. vacuum has no purpose on a racecar at all, and in my opinion neither does mechanical.

Most of the time all your mechanical advance is in by 3000 or so anyway. Unless you get below that rpm on the track the advance isnt doing anything while racing.

leapinlizard
Dirt Freak

Total posts: 402
posted October 07, 2005 07:33 AM  
cam walk and oil pump pressure on the dist. will cause timing to creep at rpm. It's best to check it at a higher rpm as well as a lower rpm so you can compensate. Just rev it a few times while watching the light to see if it's moving around.

racer55
Dirt Newbie

Total posts: 3
posted October 15, 2005 11:45 PM  
for some of the lower classes that are required to run "stock" stuff timming can be a little more controlled if you take the vacume advance off and weld the rod to the mounting plate on the under side and then reinstall the vacume advance.
tech guys wont see the alteration if you paint it afterward and your breaker plate is less likely to move from the diaphram giving under racing conditions or really anal rules that make you connect your ported vacume hose.

NJantz
Dirt Forum Champ
Total posts: 755
posted October 17, 2005 07:18 AM  
The pro's of locking out the distributor are you've got less moving parts that wear out, get sloppy, and break when you're running good. Also, when you go to set the timing you know exactly what the heck you've set. If you set it at 36deg., it stays at 36, makes it simple. That's one less thing to contemplate when you melt down a motor and wonder if it was timing or fuel that did it.

The con's of locking out the distributor is you need to spin the motor over then throw the fire to it. Other than that I can't see any reason not to do it. Idle is fine.

Locking the distributor can be done with the HEI or MSD. You can weld up your HEI or buy a kit for it. On the MSD you just rearrange the pins and it can be locked.

No matter if you go HEI or MSD, I'd get it locked out.


oldfordmod
Dirt Full Roller

Total posts: 46
posted October 17, 2005 08:48 AM  
When locking a distributor, always check that when the reluctor (the part with 8 bars that rotate) lines up with the magnetic bar, the rotor centers on a spark plug terminal in the cap. This is especially important with stock distributors which have a vacuum advance plate.

James Ott
Dirt Maniac

Total posts: 131
posted October 18, 2005 08:04 PM  
Unfortunately we have too run stock. But I might try to plug the hole on the vacuum pot. "Stock" at our track means unmolested as the factory made it, unless otherwise stated. Does anybody know of a stock appearing ignition module that is better than the GM deal.

Back to the Archives