tz375 wrote:Kris,
I have seen a couple of small pictures of Harpower motors but have no details. Can you shed any light on them?
Courtesy of Google, Tired Iron Racing (not sure if they are still active as the site hasn't been updated recently) have some information on the Harpowa engines.
Yea, that's Keven's site. He is always on the look out buts and pieces.
Not sure if I mentioned it but Oily Tom at MPE in the UK, got his first castings back from the foundry for his TR750 dry clutch kits. Still more work to do but promising...
I sent him a set of the Nova steel water pump gears (TR spec) and the non-magnetic taper for the Krober ignition for duplication.
I am under orders to make up some of the clutch adjustment brackets that bolt to the top of the case, to secure the clutch cable and adjuster.
Okay- where do I get these barrels ported for the best bang for the buck porting job? What is the best choice for piston, pipes to get this ever so streatable HP? Which Carbs?
I was looking at the reed conversion, and I don't see any numbers in actual HPs to see if there is a cost-effective HP gain in that direction!
Let's see, I think my GT 750 is a 73, will have to look again- that is the only year with the three into four exhaust, right?
All stock GT750's regardless of the year are 3 into 4 exhaust. I think it was in '75 ,someone correct me if I am wrong, they changed the exhaust header pipes. GT750's lost the crossover link tubes between the head tubes. Therefore there are two styles of GT750 stock pipes, but all 3 into 4.
GT Tim wrote:All stock GT750's regardless of the year are 3 into 4 exhaust. I think it was in '75 ,someone correct me if I am wrong, they changed the exhaust header pipes. GT750's lost the crossover link tubes between the head tubes. Therefore there are two styles of GT750 stock pipes, but all 3 into 4.
Correct Tim - some good additional info on model differences is here.
Ian
If at first you don't succeed, just get a bigger hammer !
If you want to keep it simple, send the barrels and head to Scott Cough at SCR, or Eric that owns this board and is the driving force behind it.
More power requires larger ports. Larger ports usually need to be taller and that eats away at streetability, so it's a series of compromises
For pipes, the simple answer is a set of Jemcos. They are cost effective. Swarbricks are great but need the right porting to work with. You could design a custom set of pipes using any one of the available pieces of software and then model the outcomes using MOTA and then take three or four different designs to a dyno to test
Pistons - stock work fine.
Carbs: Stock are cost effective. You could try boring them oversize or buy a set of 34mm round slides or even 34mm flatslides. Flats will provide better midrange throttle response, but cost more. 38s are better for top end and on a high HP motor you could end up with 40's. But for the street I'd suggest the cost effective sweet point is 34mm round slides.
Reeds: As Dave explained, reeds don't provide any more power but they can restore mid range lost through larger port-time areas in a tuned motor.
The reason there are no published numbers is that it take so much work - mental and physical- to make them work, that people that do all that work, aren't usually in a great rush to give away all that hard earned knowledge. there's a guy in Australia with a 100cc 200hp target motor and he has spent years experimenting with different combinations learning what works and what doesn't the hard way. Sometime we get to see little teasing glimpses of what he's doing.
Dave has invested a huge amount of time and energy on his project with assistance from a small team of people who want him to succeed. Dave has been exceedingly generous in sharing so much of his journey with the rest of us.
If you want to do this on an installment plan, there's several ways to approach it. If your motor is is in great condition, just add pipes for now and do the rest later.
If it needs to be torn down, get the barrels ported at the same time, add a little compression and enjoy the smooth overall increase until the pipes are affordable. Add carbs last in terms of bang for the buck.
Probably the best example of a tuned/hopped up GT750 is Lane's Blue Boy. It's beauty lies in the elegant simplicity of execution. 34mm rounds, ported, Jemco pipes and 80hp. Most people end up with less HP for more money.
TZ speaks many words of truth, although I have to see that 100 cc bike with 200 HP. I would have thought that it would take at least 1000 cc's. Onto the subject at hand, I was surfing through fleabay and came across a set of 34mm round slide Mikuni's, with cables and all, from a three cylinder Polaris snowmobile, and of course, I couldn't help myself. I acquired them for the paltry sum of 50 odd dollars including shipping. Cheap way to start the process, and the jetting may be instructional. The 32's are just not cutting it in the top end. Its a fascinating journey, and the stories on this board definitely add to the intrigue. Cheers.
Fred
So Mr Cruising, are we ready for that reed valve induction, boost ported, spacered, barrels and custom chambers yet? We need a few more 100+ hp GTs to rock the world.
For a complete drop off and pick up service, I'd ask Eric who owns Sundial.
Or I can strip it clean it, send the crank out for a rebuild, work out the porting and get it machined and ported to give you any number you want at the rear wheel within reason, but if you want reeds and boost ports and over 100hp the price isn't for the faint of heart whoever does it.
How much, if any would you like to do yourself? Strip and clean, assembly, perhaps. maybe fitting the motor and setting it up, or would you like to have the bike dropped off and pick it up with x hp at teh rear wheel and have someone else do all teh work including jetting and dyno work.
I have to farm some of the work out, it is time sensitive build for a showing of design and frame work, for my business. I will probably want the motor to be plug and play as much as possible to save time.
I've read this thread more than once and thought it may help a little if I provided some information on configuration:
Motor - 1974 L model
race porting loosely based on TR750 exhaust and transfers.
stock 70.5 mm pistons with balanced stock rods/pins/bearings
stock crank
squish head inserts
JEMCo chambers with cans
38 mm Mikuni rounds
100+ RWHP at 8000 rpm (Jemco's are operating near their limit)