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Post by colinjay on Jan 21, 2008 16:17:51 GMT -5
Hi all,
I took yesterday off work to make a trip down to the Big Smoke (Adelaide) to have my newly completed racer run up on a dyno (Competition Conversions in Hindmarsh).
Running the bike with a short header and the open reverse cone megaphone (as pictured in the post "Reverse Cone Megaphone), it sounded oh so sweeat reving though the gears to 8000. A bit load though, as even though I had ear muffs on my ears are still ringing this morning.
Any way, after a bit of mucking about we got the jetting sorted out, dropped from a 280 down to a 230 main jet and a from a 35 down to a 20 pilot jet, the rest was spot on. The old girl peaked at 43HP peak and was still making 40HP at 8000rpm. It is a bit flat, well actually it the power takes a dive between 3000 and 4000 rpm, but above 4000 it goes ballistic.
I fitted one of my quiter exhaust systems and got an instant drop of almost 9HP and no power above 7000 rpm. So I am going to have to find a way of making my little megaphone a bit quiter.
Interestingly, the guy running the dyno was shocked that the old girl made so much power, he said he expected some where in the mid 30's and even I was only thinking high 30's. He showed me a print out for a late model Honda CRF450 that made 46HP a few days earlier, which proves that Yamaha must have at least got the basic design right 30 odd years ago. Also not bad for an engine that was originally hotted-up in 1980! using components and technics that are now considered old fashion and inferior.
CJ
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Post by milkman on Jan 21, 2008 20:35:17 GMT -5
Good work mate
For interst the CRF450 was the bike the Aussie fella from Kiama (shameless self promotion for my home area) used to jump 96 metres in Vegas for the offical world record (106 apparently in practice)
So with similar power on hand, get out there Evel......
(i dont want comparisons on weight, lets just pretend/assume the SR could make it)
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Post by curly001 on Jan 21, 2008 22:12:47 GMT -5
That confirms it drinking cows milk straight up rots your brain! All that clean living in youth has affected your common sense Milky. I think your brain might have turned to milk, lite white even. Are f**king kidding an SR struggles to jump a gutter let alone 106mt r's. (I've opened up another can of worms)
Curly.
The opinions/comments in this reply are the ravings of BOFB and are to be taken in moderation with a healthy dose of alcohol
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Post by StewRoss on Jan 22, 2008 1:31:04 GMT -5
Heh, heh...coming to the KVR again Curly? SR  |
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Post by fenz on Jan 22, 2008 6:15:40 GMT -5
Nice power figs. CJ I have made the reverse mega from the design you sent me but have not installed it as yet(have to make header pipe). Hope mine makes similar power to yours,what has the motor had done to it?  |
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Post by milkman on Jan 22, 2008 15:16:28 GMT -5
Now now Curly, once again, no argument against my loss of mind again, but i wont have any of that milk bashing.
Stops the bones cracking from those SR vibes.
(and I wont tell anyone I know you love the Lite White on your Special K in the morning with your skinny latte)
I did say "lets just pretend/assume the SR could make it"
Maybe in a HL500 frame? Great power figs none the less
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Post by colinjay on Jan 22, 2008 16:31:18 GMT -5
Fenz,
The engine was first buit to these specs in 1980, using a second hand camshaft obtained from one of Dave Basham's (anyone who know SA MX from the 1970's will know who Dave Basham is) old TT500 MX bikes, and copying most of the other specs of his engine. The details are as follows;
modified 11:1 wiseco Piston (cranking about 12.5:1 with the planed head & a compression plate, cranks about 14:1 with out the compression plate)
gas flowed and planed head (done in 1980)
S&W valve springs (STD yamaha valves)
WEB 88A Cam (1/2 mile dirt track cam)
38mm VM Mikuni carbie (two stoke carbie)
TT500 flywheel magneto and points ignition system
Home made reverse cone megaphone on a very short header pipe (too short)
102 octane unleaded race fuel ($3.90 a litre!! on Monday 21-1-08)
Gearing: C/shaft 17T, Rear wheel 42T
The dip / loss of power that I am getting between 3000 and 4000 rpm is probably due to the exhaust being too short and also the carbie not quite being the correct type for a 4 stroke. The guy running the dyno (can't remember his name) said that I could probably pick up another couple more HP at the top of the rev range using a descent (modern) ignition system, but then he sell DynoJet equipment and would probably like to sell me a $1000 plus ignition system.
Curly & Milkman,
Back in the good old days, about 1978, in Broken Hill at a local SCMCC gymkana, one Pies Lakes jumped a stock XT500 over 100ft (30m) off of a jump that was basically a 6ft plank proped up on a 18 inch block of hardwood. This feat took place on a the front straight of a 1/2mile dirt track (oval) and you had to line up the jump (12" wide plank) as you came out of a corner. When Pies landed he was going so fast that he didn't make the the first turn and hit the wall in a fairly spectacular crsh. As far as I know his jump was a record of "The Plank", and it was pensioned off and not used again after that day! On the same day I had, had a go at the jump on my 1978 Husky 390 and actually looped it, landing basically on my back! None to say I didn't have a second go and still have great respect for what Pies did that day.
CJ
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Post by fenz on Jan 22, 2008 20:53:25 GMT -5
CJ
That is some decent comp. you are running there.
My bike will most probably never make the dyno as there is no one down this way that has one.
My engine is only on the mild side
10:1 wiesco 1mm oversize
Mild port job on the head
Ivan tighe race cam with heavy springs (stock valves)
36mm mikuni (also have 38mm flat slide to try)
Gearing will be 17-44 (rear is still undecided)
Long down swept header with reverse mega (noise permitting)
Points ignition as its an xt motor
Not expecting to be any horsepower hero but should be a good package for high 30s (hp)
Bit of a set back with our local track (Mac Park) was resurfaced again before christmas and still seems to be no good (coldmix surface crumbling)
So all race events and track days have been put on the back burner until they work out what they are going to do with the surface.
Might have to get the bike going and attack the back roads around my place......
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Post by StewRoss on Jan 23, 2008 2:46:28 GMT -5
Hi Colin, DB is a good mate of mine... SR  |
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