Tuning Help

Discussion in 'PSI Superchargers Tech Questions' started by RLPRACING, Feb 10, 2009.

  1. Mike Canter

    Mike Canter Top Dragster
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    Outlaw, I think slipping a converter is like slipping a clutch. You are never going to make power and good ET slipping either. I believe that his motor wouldn't drop as much is the rear gear was up around a 4.56 or higher. The reason the RPM dropped is that he can't pull the 4.10 gears. Don't you think that you would first put a 4.56 gear set in there and then see how the converter does?
     
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  2. Will Hanna

    Will Hanna We put the 'inside' in Top Alcohol
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    gear

    I'm with Mike on this one. I've tuned a pretty fast converter car that had some jake-leg driver:D, and it had a damn tight converter in it. I think with that gear, the looser you get on the converter, it's just going to try to blow through the converter rather than really pick the car up. Will it make it a little faster? I could see freeing up the motor would help, but the bottom line is in a heads up application, 4.10 is too tall a rear gear for the horsepower he has. A TAD runs a 4.30, so it stands to reason a roots small block is going to want a 4.56 or 4.71 for 1/8 mile purposes.

    Changing the converter at this point will be decieving. Bottom line the car has the wrong gear in it for heads up. Now if you were running a dial in class like Top Dragster, you probably got a pretty good set up. But if you're trying to get in the 3's, it's not going to happen with that gear or a lot more HP.

    If you change the gear, which it needs regardless of the converter, and you think it's too tight, then change it. Just remember slipping the converter is wasted motion. I don't know of many real fast converter cars with real loose converters.

    Tire size has never been mentioned, or roll out.
     
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  3. RLPRACING

    RLPRACING Member

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    Tire Size

    Hoosier 34.5 x 17 x16 with roll of 110"

    :)Keep talking, we will get this thing in the 3's, at least on paper. Too bad we have to wait till May to prove it!
     
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  4. hemi altered 378

    hemi altered 378 Blown Altered

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    i will give my 2 cents on this one.......why not. i think thats ALOT of tire for that car. i remember when Rick Santos brought the little chevy to Indy, car had a 33" tire. your tire is pulling the motor down at the gear change, as well as your gear ratio is a little tall. 4.56 with a 33" tire would be a great place to start. i'm not trying to offend anyone, but there is NO WAY that you can pull that tire......it's gonna shake if you don't have enough power to pull them. just something to think about.
     
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  5. Outlaw68

    Outlaw68 Member

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    Guys I can only tell you what I see, I help more than a few convertor cars, and the difference in gear ratios with what he has and what you want him to have is about 500 rpm at the finish line. A blown HEMI TAD operates in the 9000 rpm range. To compare a TAD to this combo is not apples to apples. The car should not drop that much on the shift The fuel system is flooding the motor when it shifts and cant recover. I worked two season with a convertor guy and my car and a couple other guys cars. If he changes the gear the convertor graph will look the same. Now he may need a 4.56 or 4.71 as well. But the convertor is still wrong. I think
     
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  6. Mike Canter

    Mike Canter Top Dragster
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    Well I agree that a 500 RPM increase from a 4.10 to a 4.30 gear is close to correct and to a 4.56 is another 500 rpm so moving from a 4.10 to a 4.56 is close to a 1000 RPM increase. The problem really doesn't have much to do with the mathmatical increase in RPM at the finishline but if the motor can pull the rear gear with the size tires with a 1:1 gear ratio. In this case with his size tires and the 4.10 gear ratio the RPM will drop at the shift and will not be able to recover and climb back up in RPM so you will see a big slip in the converter and no boost and no therefore no power. The motor will pretty well flat line to the finish line. We see this a lot in blower cars with or without a converter it doesn't make any difference. On a clutch car the clutch will have a hard time locking up in high gear just like a converter slipping.
     
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  7. Will Hanna

    Will Hanna We put the 'inside' in Top Alcohol
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    pump speed

    I don't know how close he is on his fuel system, but in reference to your statement it's flooding the motor on the shift, I disagree. That big of a dip in engine rpm also makes a big dip in pump speed which leans it out. With the tight converter and tall gear, it's really laboring the motor. Leaning it further here could lead to detonation since the motor is lugging with lower pump speed.

    "Flooding" ususally occurs at the upper rpms when you have more pump speed and either it's just too rich on the main jet, it has too much nozzle area, too big of a pump for the application or the heads just can't flow enough at a certain rpm.

    Like I said, the car may in fact want another converter, but when possible, it's better to make one change at a time. I would prioritize it as 1. gear 2. tire size 3. make those two work together 4. converter.

    Let's not forget with the lower gear the car will get into high gear quicker, so you can't just do the math at the finish line. The driveshaft graph looks like it never gets on the tire the entire run. It looks like it hooks, the multiplication hits the tire and starts to get it on the tire, then the gear pulls it back down. I'd be willing to bet in your shake runs, that's where the tireshake happens. The driveshaft down track looks to just be 'waddling' on the tire- lazy. Typically dragsters are the most unstable when they are doing this opposed to when they are trucking down track- on the tire.

    Goodyear tires are a little looser early, you may want to try a set of them if you do a tire switch. If you have a local Pro Stock team, you may even get on a deal where they let you take new tires to the track to scrub in. Most will gladly let you scrub some tires in for them. They'll probably tell you to do the meanest burnout you can all weekend, then take the tires back from you with a smile. Nothing like burnin someone else's rubber :D
     
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  8. RLPRACING

    RLPRACING Member

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    It seems I have to forget a lot of things we learned bracket racing. The gear, converter and the tires were all picked based on knowledge gotten from a 7.35 180mph 1520lb(total weight) bracket dragster. That was a light dragster that needed good conditions to repeat numbers or we had to back off a couple .1's. So I agree we need to change the gear to either the 4.57 or 4.71 to get the rpm's up at the finish line. I thought the converter was a little tight but now you throw in the tire size and I wonder how it will ever get traction. If you look at the graph you can see spikes where it is losing traction. You are right, it did shake the tires all the time and by making these changes it will get better??!! Is that what you call "getting up on the tire"!?!
     
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  9. Will Hanna

    Will Hanna We put the 'inside' in Top Alcohol
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    on the tire

    Often times tireshake is associated with too much wheelspeed, then thought to be too aggressive. Shake can also come from falling off the tire, or getting right on the verge of getting on the tire, but just not having the ass to get there.

    "On the tire" is when the tire goes from a squated position to the tall growth postion. Obviously, the faster the car is going, the tire is going to grow more. Getting the car on the tire refers to how quickly off the launch you get the tire from a squatted state to "on the tire." This also shouldn't be confused with running so much tire pressure the tire doesn't squat.

    The thing with torque converters is the torque multiplication. When the converter is multiplying good, it can pull a lot of gear and damn near blow the tires off. Once that converter quits multiplying as much, which in your case seems to be around .750, now you have to go back to hp, gear and weight. This is where your car struggles because you just don't have the hp to pull that gear at the weight your at.

    When you go to the smaller tire and lower gear, yes, you open up a new can of worms getting the car off the line. As Norm Grimes puts it, for every gain you make, you have to pay the tax man somewhere. If you don't have some sort of digital controller on that MSD 10, I would get one and control the car with timing off the line. A fast converter car should be able to blow the tires off the line just about anywhere. You're going to have to control that with timing or fuel system.

    With our Lencodrive FC's, we pulled a lot of timing out at the hit, then the trick was to see how quick you could ramp it back in. You may have to pull as much as 10 degrees out but you should be able to get it back in somewhere around a second. If you did tires and gear at the same time, probably start out with 10 degrees out for half a second, then ramp it back in by 1.2 or so. Then just start playing with how much to take out and when to get it back in.

    When you get it right, the car should jump right up on the tire and check out. It also is going to be more violent, and if you want to go fast, you're going to always have to push the edge.

    That gear and tire change should wake the car right on up. Typically a dragster likes to hit the tire hard on the launch, it bows the car up and makes it do what it's designed to do.
     
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  10. partel

    partel New Member

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  11. dlewis

    dlewis New Member

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    Not to highjack the thread but have been following it closely as our combo's are pretty close but different. I to have a blown sbc (although not as big, 355 ci) in a dragster w/ a standard 10-71 25% over making 33# of boost and geared 4:10 and have always thought my gear was wrong, the one difference being tire size we run a 33x16x15 Hoosier. Best e.t. to date is a 4.36 at 162. By looking at your graph I launch basicly the same rpm, shift at 7000 rpm and go thru the traps at about 7400 rpm. Have always felt that the motor was being lugged down in high gear hence the low rpm thru the traps and with what Will and Mike are saying makes sense, so I guess a gear change is in store for me to. Thanks for the info this is exactly why I check this place out every day.

    David
     
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  12. Outlaw68

    Outlaw68 Member

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    another reason I love the site.
    I hope he can make a gear swap and show his graph again. I am interested in seeing what the rpm drop is on the shift with the new gear. I wish he had a fuel psi line ..
     
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  13. pop

    pop New Member

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    what altitude are you running at?
     
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  14. Will Hanna

    Will Hanna We put the 'inside' in Top Alcohol
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    advise

    i think 4 pages of replies should be a lesson to the newer guys you can ask 5 people and get 5 different answers, and none of them may be wrong. one may be more right, but when asking advise, it's important that you take one person's advise and not try to do a mixture of everyone's advise. usually they don't mix.

    there's a lot of truth to the saying the only advise you can't afford is free advise.
     
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  15. Dale H.

    Dale H. Member

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    I think history will show that most good running cars use a rear gear that is calculated to the max engine rpm deemed possible at the finish line.
     
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  16. partel

    partel New Member

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    RE "New Guys" - for example, last season was first blown alky motor for me, (Big M 540 + 8-71, bird, E110 pump). Did read this forum for 5 months, calculated jets by Szabos book, even wrote my own "jetsize" in Excel to make calculations faster.

    25 passes, zero problems, even increased OD 25->37.5->50. Granted, didn't lean it out much (60% burn on plugs). Biggest lesson for me was how much hot weather affects.

    So a complete beginner can do ok with a reasonable amount of common sense and some homework. I somewhat know what change affects what, trouble is, how much to change to get desired effect. Testing isnt very cheap. This is where experience is quite useful.
     
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  17. Outlaw68

    Outlaw68 Member

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    How very true, the last post is. This forum has helped me alot with the blown stuff, I am a NEWBIE as well with BLOWN ALKY, just not a newbie in the sport. I test probably more than most here, with us owning a dragstrip it helps, and I can tell you that my suggestions are not only something I have tried but something I have proven. I have alot of help from some of the greatest Blown ALky tuners in the country, the problem is.. MOST of them have never ran a torque convetor in anything other than the tow truck...

    A Torque convertor and a clutch are NO WHERE in the same ball park. A clutch will slip, and convertor is a torque multiplier, a convertor does slip but it also multiply's torque. You can put a 6.00 gear in that car and its still gonna fall back to the lock up on the convertor...
     
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