Changing the shift out on a 79 SRX

YOU REALIZE 16-35 GEARING IS A 2.188 RATIO. YOUR ABLE TO SWING THIS GEARING, THAT SLED FARR FROM STOCK. SEE THIS IS YOUR PROBLEM. LET ME SAY YOUR CORRECT, YOU DO NEED TO GEAR DOWN FOR DRAG RACING 500 F.T. BECAUSE YOU NEED E.T. NOT MPH. BUT YOU STATED YOU RAN 73 IN 500 F.T. , WONDER IF YOU WERE STILL GAINING MPH WHEN YOU WENT BUY THE GUN OR WERE YOUR NUMBERS STUCK ON 73 AND YOU WERE SAYING '' I NEED MORE PEAK '' 3:16 (yammie tony)
 
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Sanka said:
comet 102



I was under the impression that a 2.0 gearing is what I needed to be close to for grass draggin in 500'?
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Sanka, you are doing just fine. It doesn't matter if you run a 102 or a 108 it will run the same unless you run a wider belt. 16/35 is perfect! Continue like you are doing and lighten the weights. That is as long as your clutches are in good condition. If they are dirty or in bad shape you will get "hang up" or inconsistancy. The other thing that will do that is the wrong weight profile. With the "in-out" scenerio, if all else is OK, you need a different profile or cam angle combo.
 
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problem is with the old srx is there was only 2 yamaha helix ever made, (maybe some aftermarkets??)1 is a straight angle helix and the other is a yamaha update multi angle helix, I dont know if its even available anymore new. Also with the age of it the secondary spring would be tired by now. Let me see if I can dig thru my old srx notes and find the helix part numbers and angles for you. I had a complete secondary here with both helix and brand new rear spring, just sold it to a member here this spring.

I like your gearing for 500ft, with those banjo string power curve motors they liked alot of gear and it was almost a little easier to stay on the power curve, cause its pretty narrow.........ahh yes the old srx440 days...LOL
 
I ran: 16/33 gearing, N mod weights with extra notch, purple spring, 2 shims under spider, 1106 belt, was 6000rpm engagement speed and 9000rpm shift. I am still looking for the yamaha helix angles for you in all my chicken scrath here.

I also will tell you I took a extra jackshaft and had the one end stubbed, made to fit a arctic cat secondary clutch on it with a keyway, this opened up the wide world of every helix known to man and I have the best helix down as the 48/40 was the golden one
 
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Awesome Mrviper! I'm putting that in my notes. Is that gearing for 500'?
 
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HEY SANKA, I,AM TELLING YA A 2.188 GEAR RATIO IN THAT SLED IS KILLING YA AGAIN IF IN FACT THIS IS A STOCK 79 SRX. TAKE THAT TO THE BANK. THERE WERE TWO HELIX,s FOR THE SRX,s 1976 THROUGH 80 ALL THE 440,s USED THE STRAIT ANGLE AND THE 76 340 SRX USED THE MULTI. NOBODY OFFERED AFTERMARKET FOR THE SRX. YOU HAD TWO TO CHOSE. !! 3:16 (yammie tony)
 
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ok Tony, I am gonna have to ask, why would deeper gearing in a srx that has NO LOWEND power or TORQUE be hurting it? we are talking 500ft drag racing, moving a sled from a stop to a finish line in the quickest time possible, we are not worried about mph, but elapsed time? just curious as why to your thinking.


I have been looking now for a hour on those helix, do you have the angles and part number of the multi written down?? I thought I had it from one of my yamaha grass drag manuals, but I cant find those right yet,this stuff was put away deep in my junk.
 
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I CAN TELL YA I HAVE A GUY HERE IN NY THAT RUNS EVERY YEAR AT JACOBEYS WITH US. HIM AND HIS TWO SONS RUN TWO 78 SRX,s AND A 1980. ITS REALLY FUNNY THEY BEAT ALL THE NEW 500,s 600,s AND I,LL TELL YA THEIR STOCK BUT VERY FINED TUNED. THEIR RUNNING EASY HIGH SEVENTIES TO MAYBE EVEN A 80 mph WITH A 1.95 GEAR RATIO. POSSIBLEY 2.0 TOPS!!! I HAVE ALL SRX HELIX INFO. 3:16 (yammie tony)
 
Without knowing the e.t. of his run hard to judge it good,bad soley off mph, because the less time you are on the track(quicker) the less time you have to build mph in a short distance. I posted what I used in my 1980 srx that had a 79 engine and carbs,skidframe in it, then I bought a nice 79 and did the full monty on it with Aaen. Back then we raced in fields at backyard races with flags and simple light bulbs for the win light in your lane...LOL!! Mine always liked the deep gears, these things have very narrow powerbands and the lower gearing makes it easier to hang onto it, it also allows you to pinch the belt a little better with more weight. Theres a million ways to clutch a sled.
I sit back and read his post and it looks like a tired secondary spring to me if he has exactly the rpms and downfall as what he posted he has and everything is working correctly. He is simply overshifting from lack of secondary spring tension and I would guess the reason he is slipping the belt up top, I would guess the rear clutch is pretty warm after a pass or 2.
 
Yep the rear clutch gets warm and after a while the belt transfer that heat to the primary. Doesnt take many runs (2 or 3) and the clutches are polished agained and then need to be sanded.

The helixes that were available for the srx's were 42 degrees (8A5-17624-01-00) 39-45 degree 8A7-17684-01-00
 
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DON AND DYNO, LETS LOOK AT THIS A MINUTE. I AM CURIOUS TOO. HE NEVER POSTS E.T. ONLY HIS MPH IN 500 f.t. ( which really ain,t awful) BUT YET YOU TWO SAY HE IS DOING FINE RUNNING A 2.188 RATIO ON A STOCK 79 SRX. SO WITH THAT I ASSUME YOU TO THINK 73 mph IS CLOSE. LOOK AT HIS ORIGINAL TOPIC, '' I NEED MORE PEAK '' NOW I WILL KICK IT BACK TO YOU GUYS, PLEASE EXPLAIN THAT. WHY IN HIS HEAD DOSE HE NEED MORE PEAK, COULD HE RUNNING OUT OF GEAR ? COULD HE BE OVER RPMING, COULD HE BE LAYING OVER. IF HE CAN RUN HIGH SEVENTIES WITH A 1.95 RATIO AND STILL BE ACCELRATING AT THE GUN, WON,T HIS E.T. INPROVE. I FIND IT VERY HARD TO BELIEVE YOU TWO THINK A 2.188 RATIO IS CORRECT ON A STOCK 8800-9000 RPM MOTOR. LOOK, BOTTOM LINE HERE IS I NEVER RAN ANY OF MY SRX,s GEARED THAT LOW. NOT EVEN A PRO STOCK 79 SRX I HAD FULL MOD AAEN/ PSI BUILT OR MY 77 SRX. 3:16 (yammie tony)
 
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Sanka said:
Yep the rear clutch gets warm and after a while the belt transfer that heat to the primary. Doesnt take many runs (2 or 3) and the clutches are polished agained and then need to be sanded.

The helixes that were available for the srx's were 42 degrees (8A5-17624-01-00) 39-45 degree 8A7-17684-01-00
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You bring up something here that I have always wondered about. Sheave face preperation. I am no expert on drag racing but it seems that there are 2 schools of though on this subject.
I see many that sand or scuff there clutches all the time and some after every run saying that you need to have a scuffed face to grab the belt and stop slippage. I have seen others that polish the face to a mirror finish and keep it that way. They say that your belt is like a basket ball shoe and the face of the clutch is the court in that a polished sheave and a belt broken in to run on it will not slip and won't need constant attention. They also say the scuffing the sheave will in turn scuff the belt and every time you do it things change and so does your consistancy.
I see the theory behind both arguments but have never done enough racing or testing to come up with an opinion of my own. As long as all the old school race gurus seem to be following this thread I wonder what their opinions are on this subject as well. It must be part of a proper setup as everyone does something to their sheave faces so whats the best "scuffed or polished' and why.

opsled
 
What mph should I be seeing in a well tuned 79 SRX in 500'. Am I expecting to much from the 440 cc motor. I was hoping to hit 80 atleast. I'm use to driving newer sleds and maybe I am asking too much from the vintage iron.
:nos:
 
PHIL, I ALWAYS SCUFED ON THE OLD IRON, ESPECIALLY WHEN USEING A NEW BELT OR ONE THAT HAD VERY LITTLE USE.
SANKA, I DON,T THINK YOUR BAD AT ALL HERE. YOU HAVE BASISLY WHAT I RAN IN FIVE SRXs YEARS AGO. ONLY DEFFERENCE IS I WOULD NOT RUN THAT LOW GEARING. YOUR ENGAGEMENT IS PERFECT, NOT GONNA BE LAZY AT 5500, YOUR RPM IS ON THE HIGH SIDE . SEE WHAT YOU HAVE HERE IS DEFFERENT OPINIONS, SO ONLY WAY TO KNOW IS TEST DEFFERENT SET-UPS. IT BE NICE ALSO IF YA HAD YOUR E.T. !! YOU MENTIONED YOUR MPH ONLY HERE, IT COULD POSSIBLEY BE BETTER, BUT THEIR RIGHT E.T. WINS RACES. 3:16 (yammie tony)
JUST SO YOU KNOW AT A 2.188 GEAR RATIO WITH THAT SLED, YOUR TOP SPEED IS 78.88 MPH. SO IF YA RAN 73 THATS GOOD. I STILL SAY YOUR TOO LOW.
 
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God how did you figure out the top speed for 16-35 gearing? Also is the clutch on the srx a 30mm flush taper clutch. My comet does not fit as far on the crankshaft as the yamaha clutch did. Its about 5mm shy. Are you on a instant messenger service?
 
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Tony, you would actually lose more rpm on the overshift with taller gearing, the motor would be pulled off peak alot easier the taller the gears are and we only have a 3000rpm power curve here, the peak at 9000rpm. I think what he is thinking he is losing is when the tach falls back on rpm as I am sure its leaving good then loses rpm then climbs back up, from overshifting, and or slipping the belt, a worn secondary spring, slipping the belt in the back can do just that. If he were over geared(ttodeep) he would actuallyover rev badly the more distance he went, as once the clutch has reached its full shift out the speed will stop yet the engine will over rev. The other thing I ask is a playback tach used? as the stocjk tach is pretty small and hard to watch especially 1,200 rpm going down the track not too mention its down by your waist.

Theres alot of differnt ways to clutch a sled, the srx440 is a very frustrating little machine with its narrow peaky power curve, I liked to gear them deep was easier to control it and they went quicker, not faster mph, but quicker, but it also has alot to do with the clutch set up, more gear allows you to use more clutch weight, less gear less weight. The arctic cat secondary was the biggest single improvement I made, it literally made the sled come to life, the springs and helixs you could fine tune any condition you came across.

Phil: I scuff my clutchs with scotchbrite pads, I have heard both sides as you have, its just what worked for me.

for your speed calculator formula you just use:rpm/gr/ x sc/5280=mph @1;1 clutch ratio

RPM;-rpm of the engine
GR;-gear ratio
SC;- sprocket circumference, which is 22.68 on std 9 tooth drivers

/= divide
 
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