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I have a 89 suburban and the dist is the original one. I have also switched to a 30" tire coming from a 27" tire, if it matters. I would like to improve my low end,to get the heavy vehicle moving and maybe gain a little in fuel mileage. The D.U.I. Distributor claims to give full spark through out the entire rpm range. Do you guys think 300 bucks is worth it for the dist? You guys have any complaints that have one?
D.U.I is Davis Unified Ignition, it's a souped up ( for lack of a better term ) GM HEI, nothing more. MSD would give you more, cheaper. fire a GM HEI with a MSD 6A box. D.U.I's are great for engines in which there all that is available ( 200-250 I6 Fords, it's them, factory Duraspark which could be fired with MSD, or Mallory Unalite )
I've ran some of the DUI units in my cars, they work great and are far more durable then a lot of the MSD stuff I tried. Probably not the ultimate in performance ignition systems, but plenty good enough for street use.... As far as the $300 distributor, probably more then you need in the sub. One of the good HEI aftermarket distributors would be fine, or maybe even just installing the HEI coil and cap unit that Accel sells would probably work excellent. Hotter spark should fire the mixture better, maybe a minimal increase in mileage....
BTW, the DUI units are a high quality build. They look great when checked on a scope or tuning the distributor on a distributor machine. Might not have the big name like MSD, but they also don't have a lot of the failures like the MSD boxes have.... Take a look at the pro cars, NASCAR, NHRA, road racing or whatever. They all run a dual system so when system 1 fails you can switch to system 2. Says a lot right there about the reliability issue......
a hotter spark isn't going to get you much more low end.... re-gearing is the way to regain power loss when going to bigger tires, if i hadn't been partying all night i'd remember the formula to get you back to your stock overall ratio, which will actually bring your gas mileage and a little better off the line power too.... but if you regear and get a hotter spark, she'd be running better than she ever has
I thought that by going to a bigger tire I would get a little better gas mileage, you know lower RPM's? The engine has a little mis to it at idle and through out that I cant track down and figured the best thing to do would to get a new dist. then go from there. The thing about the DUI dist that I like is that they claim it to have a custom advance curve to suit your needs and better/instant throttle response. I like the MSD Idea but will still need a new dist. I am going to check and see if the price is around the same for the msd and new dist. compared to the DUI dist.If it comes out around the same I might as well go with the DUI because I dont have to find a mounting location for a box and run wires. The motor is not that bad all it needs is a little tuning to bring it up. I know these years of small blocks are not horse power monsters because of the restricted heads/Induction but I am not trying to race the burb. I just want as much low end as I can get for pulling a trailer and getting around town.Quote:
Originally Posted by thesals
Going from a 27" tire to a 30" tire will drop your RPMs at a given speed by about 11%. It's a straight linear relationship.
RPM = MPH x Axle Ratio x 336
Tire Diameter
look on the bay for a dist. there is a clone of the dui that is about 70 bucks shipped. I have used 3 ,in fords and chevy. great product.
going to the bigger tire in effect yes lowers RPM and raises gas mileage, until you factor in that you went to a size that its harder for the engine to overcome, and due to your loss of power you're putting your foot in it more to get to speed ... its a vicious circle