Building a cheap dragbike

[Anonymous]

GS 750 is a good place to start. Already has straight cuts, big plus. Do the crank, then concentrate on basics, good valve job, ring seal, valve timing, ignition timing etc. Cams and compression will give the most bang for the buck as you grow with it. If I remember correctly GS 850 cylinder and pistons will fit. A friend of mine has been drag racing a GS750 based bike for more than ten years. Even though there are easier ways to go real fast he insisted on the 750, it is currently capable of running mid 9's (only the lower end is still from a 750). Another testament to the strength, is that Suzuki used the 750 as the base for their 1000cc superbikes in the late 70' early 80's.

[Anonymous]

Hey GTM
Yea, the 750 is plenty stout enough for the rigors of dragracing. I would like it if someone had a good set of hi-c pistons for sale. The 850's will give me some more displacement, but not much increase in c.r.
How about it friends?
Paul

[massakins]

Using a '78 GS750 as the basis for a drag bike is not a bad idea, especially if a good one is readily available. There is a wealth of used parts available and many things that interchange with the GS1000-1100 or can be easily retrofitted. Additionally, the straight cut primary drive is already in place, kickstarter allows removing entire electric starter and charging system and there are many donor 850cc cylinder blocks available. My strategy would be to make it as light as inexpensively possible, make it reliable and consistent, then make it as fast as inexpensively possible. I recommend the following:

Chassis: Use spoke wheels (GS1000 has alloy rim for front; add WM6 rim on back with 5.5" slick) instead of the heavier mags with a single disc brake on the front. Extend the stock swingarm 3-4", install struts and a wheelie bar, leave the rake alone and shorten the forks to maintain a level chassis. Remove as much of the unnecessary stock components as able. Objective is long, low, rigid and as light as junkyard parts allow.

Engine: Weld crank, install HD springs in backing plate and weld stock clutch basket on back to fuse rivets and backing plate, HD springs on clutch pressure plate, remove flywheel and starter components (kickstart only), install 850cc cylinder kit from a shaftie, mill head .020" and freshen head with valve clean and lap and new valve seals, modify stock cam chain tensioner to make manual (30 minutes and no cost), degree cams for best power, Dyna S ignition and coils. Add stock GS1000 cams if they gain anything (I've got free ones if you want).

Miscellaneous: 4 into 1 header is a must, rev limiter optional (if you are sure of your shifting), air shifter optional (if you are sure of your shifting), 29mm Mikuni Smoothbores would be a definite plus (can be pricey but always worth their cost to resell when done with them), velocity stacks, new battery and new chain.

It can be done inexpensively without being cheap. I know because I've done it. Many of the parts can be bought used and later resold for near what you paid if maintained. This includes carbs, rear wheel, wheelie bars, etc. Once this combination is dialed and your ready to go faster I'd add nitrous. Or change to a GS1100 motor. No return on the cost of pricey pistons, porting, cams etc. on the 2v GS750, IMHO. Good luck.

[skip]

I disagree with adding nitrous. Ive had nitrous on my 1150 for 16 years and found at the dragstrip the inconsistanty in et's with nitrous hurt me in bracket racing. if i wanted to be consistant and wanted to run close to my dial in i did not use it , but if i got behind due to bad launch or wheelspin or wheelie I would use the nitrous to make up lost ground . This only worked out for me a few times and usually didn't . and nitrous can be tough on parts (just had to install new cylinders due to nitrous wear and tear)

[Anonymous]

Speaking from experiance GET A REV LIMITER, one missed gear and your whole season (and a whole lot of work) can be left in tatters. 12,000rpm on an '82 1000Katana is not to be recomended

[Anonymous]

It's truly an amazing world when three people from Canada, the U.S. and Ireland can be brought together by their common love of motorcycles. Thanks friends!!
Massakins- Great advise. Just a couple of questions.How difficult is it to fit the 850 cylinders and pistons. What exactly is needed? Will the 750 cams work or will I need the 850's? What about cam chain? Valve cover, etc. Also can you tell me the advantage of gs1000 cams? I will take you up on your generous offer if they will help. I remember my last gs1000 owners manual said to use a gs750 intake cam if you wanted to boost power.
Yes, it will have both a rev limiter, a 2-step, switched clutch lever, air shifter, etc.
Lightness is the secret. The frame will be stripped of every unnecessary bracket and accessory, but I am keeping the electric start, not the charging system though. I have friends who race their bikes this way. No problem if you put the battery on the charger for a few minutes every other round.
Any more advise???
Paul

[Anonymous]

Oh, I do have stock cast iron liners and stock pistons for a gs 1000. Can the cylinders be bored and the 1000 liners be pressed in place? That way I could use the 1000 pistons as well.
Paul

[massakins]

Skip, there are many examples of nitrous powered bracket bikes running with winning consistency. My thoughts were that "once this combination is dialed and your ready to go faster I'd add nitrous". This description included a slick and wheelie bars, which will add alot of consistency and reduce the chance of wheelspin and wheelies. Very important that the combination is dialed in first.

Secondly, I added that there was "no return on the cost of pricey pistons, porting, cams etc. on the 2v GS750". Not much of a market there. But nitrous parts can be moved from bike to bike regardless of the make and retain some resale value as long as they function and are not obsolete.

The most successful nitrous bikes are using a control box similar to those marketed by Schnitz Racing to program the amount and timing of the power. With these boxes you can launch with a controllable power level and then add it with each gear or based on elapsed time as the bike and rider can best use it. This set up provides incredible power with consistency. Far improved from the old pushbutton with its on/off response. Many ways to skin the cat, these are my ideas.

[massakins]

Nasty, I "think" the GS850 pistons use the same wrist pin (17mm) as the GS750; GS1000 uses bigger (18mm). GS850 kit should be a direct swap.
No need to change cylinder head so cams are only an issue if there is performance to be gained. I'd measure lift and go with the highest lift; duration makes a difference but is pretty much the same on OEM cams. Stock cam chain, valve cover, etc. is fine, too. GS1000 cams have about .324" lift, ie when peak lobe measurement is subtracted from measurement perpendicular to it.

Lightness is key when looking for performance. If its not on the bike it won't break. Plus it doesn't have to be accelerated, leaving more power for the remainder. I saved 40 lbs removing the on-board starter and all of its associated equipment from my GS1000. If I could have kickstarted it I would have. Good luck.

[skip]

massakins,
Sorry..... I stand corrected. My nitrous system is from the dark ages with almost no electronics at all.(except for the fuel pump and solinoids)
Technology Has come quite far since then I guess. Plus because I was not running wheelie bars and had a stock tire the bike was a real handful under nitrous (not for thr faint of heart) and not that consistent.(but exciting as all hell!) Thanks for your input on the subject..........................skip

[Anonymous]

Alright, I'll go with the 850 cylinders and pistons. Can anyone help me out with these parts? In Canada if possible.
Thanks, Paul

[Anonymous]

I saved 40 lbs removing the on-board starter and all of its associated equipment from my GS1000. If I could have kickstarted it I would have. Good luck.

The 79' 850 had a kickstart option.

[Anonymous]

I saved 40 lbs removing the on-board starter and all of its associated equipment from my GS1000. If I could have kickstarted it I would have. Good luck.

The 79' 850 had a kickstart