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81' XV750 drag bike

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81' XV750 drag bike

PostAuthor: mike8492 » Sun Aug 06, 2017 8:14 pm

Hi everyone. so ive got this 81 xv750 that i've been working on for a while, and I'm getting pretty close to getting her road worthy. while i want to have my virago as a daily driver I've had an undeniable urge to race her at the track. when i bought this pet project, it came with a ton of spare parts, not a lot i don't have a second of; spare engine, spare front end, spare rims, spare tank etc. so my ridiculous plan is this: mod the ever-living hell out of the spare engine, and modify the remainder of the necessary parts so that in a single day I can un-bolt the road parts and bolt up the race parts for the track and switch back at the end of the weekend. i realize this is a long term project (2-3 yrs) and will be relying on the excellent advice of this forum throughout.

so now i'll outline the plan in more detail. to transition the bike from road to race i would: un-bolt the steering head and take off the forks, bars, front wheel all as one piece and bolt on the racing setup. swap the road engine with the racing engine with their own fuel system and exhaust setups. swap the stock seating sub-frame with a custom made, light weight one. swap the rear rim with the street tire with the spare rim sporting a drag slick. remove the electrical harness for the road (which i am currently working on) and hook up a purpose-built race harness. finally, swap the fuel tanks as one will be set up for whatever fuel system i decide to go with.

now to talk about the racing replacement parts individually:

Engine: i intend to put in performance cams, valves and springs. this will obviously warrant new pistons, which is fine as i intend to have the cylinders bored for some extra displacement. if possible i intend to home-port the heads. im not sure yet if i will use the stock clutch pack untill it dies and then throw in a barnett or an ebc, or do so right away. performance coils would already mounted on the engine as well as the new iridium plugs. whatever fuel system i decide to go with will also already be mounted in it place between the cylinders, so the engine will simply roll under, bolt up and plug in. the stator and rotor, along with the starter motor will be removed from the engine to save weight. this will mean the bike will run exclusively off of the battery, also removing the need for the r/r. this should save a decent amount of weight. this will also mean the use of an external starter, which, given the placement of the starter motor, should be an easier modification. i would also like to have the air shifter all attached ti the engine to keep the process simple.

Front end: the front end is fairly straight forward: disconnect the throttle and choke cables from the carbs (stock), disconnect the instrument cluster and lights from the harness (or maybe the harness could come right off with the front end). un-bold right at the steering stem and the whole unit comes off and the new on bolts on in its place. both front ends will be fully assembled alredy; breaks, rims and tires, and their own handle bars. the racing front end will not have any instrument cluster or lights. it will be properly lowered, and will not have a mud guard.

Electrical harness: obviously the racing harness will be built as simple as possible and supply the ignition system, and air shifter as required.

Sub-frame: as compact and light weight as possible. probably built of aluminum.

Fuel system: the fuel system is the thing i have the most decisions to make with. should i go with these performance carbs from NCS http://www.ebay.ca/itm/Yamaha-Virago-XV ... 1438.l2649 , the racing single carb conversion from BIP http://bikeintakeperformance.com/home/1 ... retor.html , or go big with a fuel injection setup? i've even been considering, if i end up making really high compression, running a methanol setup if i went with fuel injection. the spare tank would be set up to feed what ever system i go with.

so that is my vision! let me know what you guys think and tell me what you think i should do with the fuel system, what can i do about cams, valves and springs. im sure you all have lots of questions about this insane plan of mine so ask away! the more holes i can close up now the easier things will be for me later. thanks in advance for the input!
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Re: 81' XV750 drag bike

PostAuthor: rantingsmith » Mon Aug 07, 2017 12:23 am

Nice idea although as you will literally be swapping everything apart from the main frame you might as well get a second titled frame and end up with two bikes and an extra 8hrs spare every race weekend..

Plus to make the most of drag race times you really want a chain drive i.e. a XV920 you can still use the heads from the spare engine as that will give you a compression increase..:cl:

Just my 2cts.. cheers,

Rant.
The Flying Anvil XV750SE '82 - Custom rear subframe, Bar end mirrors, New indicators, New tail light, 18" rear wheel conversion, KOSO speedo, lithium battery, custom wiring harness, clipons, modified SR500 rearsets, Lucas replica switchgear, K&N air filter, many parts powdercoated
XV920 '81- Watsonian Monaco sidecar tug project-work in progress - top end rebuild time
TR1.1 '81 Basket case project - Work in progress - Sepp Koch style frame chop plus refinement, XVS1100 jugs piston crankshaft conversion, nanno's 9 plate clutch conversion, BMW r850r rear shock, spoke wheels XS650 front & rear, twin 320mm discs with Yamaha Blue spot calipers, XT500 tank, twin Webber carbs, home built exhaust (hopefully) seat and subframe, footrest hangers...
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Re: 81' XV750 drag bike

PostAuthor: nanno » Mon Aug 07, 2017 12:27 am

Sounds good, I am all for racing Yamaha XVs. Just a few things to consider:
1) There's no special-high-comp pistons made for the 750, so you'd have to have something made specifically for your application. Not the end of the world at all, but you should have some indepth knowledge on engine design to come up with something which will work straight out of the box.
2) Is there a specific reason, why you limit yourself to a 750 for racing? If not, go big or go home. :bg: The 1100 crank will bolt into the cases, only the case mouths have to be opened out. An 1100 with 750 heads is one of the cheapest ways to get to a very torquey 1100-engine, which is exactly what you want, when you start out at the dragstrip.
3) Please forget about the 2in1 inlet and those puny carbs. I run VM38s on my street setup (XV1100 with 750 heads) and they are a perfect match for the ports. There's also a TM38 (flatslide) version out there and for both setups you will find some jetting information.
4) Exhaust: The only performance exhaust available out there off the shelf is the Mac 2in1, which isn't bad at all (except for it rusts like hell, so you have to have it re-coated once you buy it) or have someone build a nice exhaust for you. I am currently running an equal header length 2in1in2 with 1 3/4" downpipes and trust me, that made a lot of difference.
5) Ignition: In order to release the horses, which are very, very well hidden inside your engine, you'll end up looking for a programmable ignition. I personally find the Ignitech TCI-P4 to be the best, together with a set of coil-on-plug - coils out of a modern sportsbike (no coil-wires, no hassle, stronger spark).

And well... with such a setup, I am more than curious to hear what kind of times you manage on the dragstrip, but be warned: There's not much room for blaming it on the bike.

Cheers,
Greg
http://viragotechforum.com/viewtopic.php?f=12&t=43227 - Nanno's accumulated findings (and blatant show-off) - infos on my TR1's, my performance and reliability mods and a bit of show-casing of the stainless steel exhausts I build

http://greasygreg.blogspot.co.at (My blog - Greasygreg.blogspot.co.at)
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Re: 81' XV750 drag bike

PostAuthor: faffi » Mon Aug 07, 2017 2:05 am

What they said; get a spare frame and go 1000 or 1100.
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Re: 81' XV750 drag bike

PostAuthor: mike8492 » Wed Aug 09, 2017 9:17 pm

thanks for the input everyone, and the suggestions, ill answer and clarify as much as i can for you all:

so first ill try and answer a couple questions at once; why don't i go with a bigger/better engine, and why not just get another frame and build a second bike?

Well for a couple reasons; because i'm really just working with what i have. and i want to accomplish this with what i have. if i need a new this or that, fine if it turns out the parts motor is worse than i thought, then, well the plan might not be worth it. kinda just thought this whole thing up because it seemed like a waste of good parts. also if this plan just outright fails to launch, then i dont want even more useless parts laying around. also, and this i really the most important reason, my better half would probably shoot me if i
added another bike to the garage lol.

Now, more about the specifics:

as for the piston situation; i did find this link elsewhere on the forum: http://www.megacyclecams.com/ apparently they make performance cams and pistons for many models including the XVs. however i have yet to verify this as the catalog is from 2012ish so maybe they're not around anymore.

that said...

Nanno, correct me if i read this wrong, but you're saying i can take my 750 engine, open it up, drop in an 1100 crankshaft with 1100 con rods and pistons, bolt on 1100 jugs and bolt the 750 heads? if so then that could save a
lot of $. and i fully agree that the re is no replacement for displacement. is the 1100 cylinder taller than the 750? if not then it may even be worth it to just bore the 750 cylinders. would the 750 con rods work on the 1100 crank and pistons? just wanna seprate what i might need and what i might want for the start. on the topic of the heads; where would be best to get new valves and springs?

as for all the rest of it: thanks for the tips on the carbs, exhaust and the ignitor. i think a pair of those
tm38 flatslides will work best for the racing application.

anymore other in put is always welcome. and thanks all again!
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Re: 81' XV750 drag bike

PostAuthor: mark75 » Wed Aug 09, 2017 10:23 pm

as I understand it there is differences in crankcase and skirt matching issues that would need to be addressed, but those things have been posted about, so a detailed search may give you the info you seek.
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Re: 81' XV750 drag bike

PostAuthor: nanno » Fri Aug 11, 2017 1:32 am

Hi Mike!

mike8492 wrote:as for the piston situation; i did find this link elsewhere on the forum: http://www.megacyclecams.com/ apparently they make performance cams and pistons for many models including the XVs. however i have yet to verify this as the catalog is from 2012ish so maybe they're not around anymore.


Megacycle is still in business and you can still get hot cams from them. They never have made 750 pistons though (to the best of my knowledge at least!) That being said, if you know a skilled ally-welder, you could weld up the pistons and make a dome onto them to your specification and then use a 920/1000/1100 head with the bigger ports and a customized combustion chamber.

mike8492 wrote:Nanno, correct me if i read this wrong, but you're saying i can take my 750 engine, open it up, drop in an 1100 crankshaft with 1100 con rods and pistons, bolt on 1100 jugs and bolt the 750 heads? if so then that could save a
lot of $. and i fully agree that the re is no replacement for displacement. is the 1100 cylinder taller than the 750? if not then it may even be worth it to just bore the 750 cylinders. would the 750 con rods work on the 1100 crank and pistons? just wanna seprate what i might need and what i might want for the start. on the topic of the heads; where would be best to get new valves and springs?


Yep, that's what I said. Yes the 920/1000/1100 cylinders are a bit taller so you need the correct headmount-brackets for the front and rear, but that's an easy job. With regards to 750 conrods, no and as the XV-models all run a plain-bearing crank and this comes in 5 journal sizes, please get yourself a complete rotating assembly from an XV1100 unless you are an EXPERIENCED engine builder (and I don't mean US-muscle cars, but smaller and finnicky stuff), because you'd have to measure and calculate all the clearances correctly and that's quite a job. New valves and springs: Get the first-gen springs of an up to 1983-model as those were harder. If you go all mad on the cam-side of things (e.g. MegaCycle) they'll specify the correct springs, but be careful high seat pressure of the springs will help with high-rev-stability of your valvetrain, but will also dramatically increase wear and tear on the cams and rockers.


mike8492 wrote:as for all the rest of it: thanks for the tips on the carbs, exhaust and the ignitor. i think a pair of those
tm38 flatslides will work best for the racing application.

anymore other in put is always welcome. and thanks all again!


Dual TM38s will not only work best for racing, but also for everyday riding... The amount of improvement in both HP and torque if dialed in correctly is incredible and it's soooo much more service friendly.
http://viragotechforum.com/viewtopic.php?f=12&t=43227 - Nanno's accumulated findings (and blatant show-off) - infos on my TR1's, my performance and reliability mods and a bit of show-casing of the stainless steel exhausts I build

http://greasygreg.blogspot.co.at (My blog - Greasygreg.blogspot.co.at)
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Re: 81' XV750 drag bike

PostAuthor: mike8492 » Fri Aug 11, 2017 6:30 am

Thanks Nanno!

so what if i went with the 750 crank and con rods, but with the 1100 pistons, bore out the cylinders and the case mouths, and make bushings for the con rods at the piston end?

i realize i wont get as much displacement, but in the interest of cost efficiency, i may have to compromise.
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Re: 81' XV750 drag bike

PostAuthor: faffi » Fri Aug 11, 2017 11:59 am

Would be simpler to fit the 1000 pistons and cylinders instead? But you will have to take out the crankcases.
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Re: 81' XV750 drag bike

PostAuthor: nanno » Fri Aug 11, 2017 1:17 pm

I don't think the liners on the 750 cylinders are thick enough to bore them out those extra milimetres. IIRC the bore on the 750 is 87 and on the 1000 and 1100 it's definitely 95.

750 conrods are a different length.
http://viragotechforum.com/viewtopic.php?f=12&t=43227 - Nanno's accumulated findings (and blatant show-off) - infos on my TR1's, my performance and reliability mods and a bit of show-casing of the stainless steel exhausts I build

http://greasygreg.blogspot.co.at (My blog - Greasygreg.blogspot.co.at)
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Re: 81' XV750 drag bike

PostAuthor: mike8492 » Fri Aug 11, 2017 3:07 pm

i see after a quick review of the bore/stroke specs i realize i got my figures mixed up. the bore on the 750 is in fact 83mm. so yea, i doubt thats taking another 12mm. it is slightly disappointing that i wont be able to use as many stock parts as i would have liked. still best to evaluate all options.

guess im off to source more parts.

do you think the increase in displacement and compression will give me enough power to launch i second gear even with the stock final drive?
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Re: 81' XV750 drag bike

PostAuthor: nanno » Sat Aug 12, 2017 1:13 pm

Just did that on accident before... :ops:
http://viragotechforum.com/viewtopic.php?f=12&t=43227 - Nanno's accumulated findings (and blatant show-off) - infos on my TR1's, my performance and reliability mods and a bit of show-casing of the stainless steel exhausts I build

http://greasygreg.blogspot.co.at (My blog - Greasygreg.blogspot.co.at)
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Re: 81' XV750 drag bike

PostAuthor: mike8492 » Mon Aug 14, 2017 4:10 pm

were you still able to pull away? if so then i can negate the issue that plagues many drag bikes: going from first to second with an air shifter.

this is actually a good segway into my next question: tires.

ideally i would have a drag slick on the rear, but where the hell do i find one that fits a virago rim? 130/90-16 is not a common size as we all know but even less commonly found in racing does anyone have a suggestion on where to find such a tire? and if they simply don't exist, what might i have in the way of alternatives?

thanks as always to everyone for the input!
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Re: 81' XV750 drag bike

PostAuthor: rantingsmith » Mon Aug 14, 2017 11:26 pm

Seeing as you will be swapping a backbone from one bike's parts into another bike's parts, get a second gen spoke wheel or a modified 535 wheel and get it laced to whatever rim you need for your tyre choice..
The Flying Anvil XV750SE '82 - Custom rear subframe, Bar end mirrors, New indicators, New tail light, 18" rear wheel conversion, KOSO speedo, lithium battery, custom wiring harness, clipons, modified SR500 rearsets, Lucas replica switchgear, K&N air filter, many parts powdercoated
XV920 '81- Watsonian Monaco sidecar tug project-work in progress - top end rebuild time
TR1.1 '81 Basket case project - Work in progress - Sepp Koch style frame chop plus refinement, XVS1100 jugs piston crankshaft conversion, nanno's 9 plate clutch conversion, BMW r850r rear shock, spoke wheels XS650 front & rear, twin 320mm discs with Yamaha Blue spot calipers, XT500 tank, twin Webber carbs, home built exhaust (hopefully) seat and subframe, footrest hangers...
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1981 XV920 - sidecar tug project bike - Watsonian Monaco sidecar to be fitted

1981 TR1 - Basket case project - bought completely dismantled and teaching me mechanics 101
Sex: Male

Re: 81' XV750 drag bike

PostAuthor: nanno » Tue Aug 15, 2017 12:09 pm

mike8492 wrote:were you still able to pull away? if so then i can negate the issue that plagues many drag bikes: going from first to second with an air shifter.


Your way of tackling the quarter-mile might be slightly different than mine... but yes, once it picked up some revs (around 2000 rpms) it pulls away cleanly. The TR1 has got a very long first gear anyway, which is a massive plus on the dragstrip.

mike8492 wrote:what might i have in the way of alternatives?


You could always fit an XJ650 rear-wheel and go for a 4.00x18 Slick. (Overhere (Austria, Europe) I can only get Avon Drag Slicks in 4.00x18, you may want to check out Shinko and Mickey Thompson.)
http://viragotechforum.com/viewtopic.php?f=12&t=43227 - Nanno's accumulated findings (and blatant show-off) - infos on my TR1's, my performance and reliability mods and a bit of show-casing of the stainless steel exhausts I build

http://greasygreg.blogspot.co.at (My blog - Greasygreg.blogspot.co.at)
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Re: 81' XV750 drag bike

PostAuthor: mike8492 » Wed Aug 16, 2017 6:41 am

yes, shinko was my first stop. but it seems the shinkos, and all the drag tires for that matter are only made for 17" rims and only come in 180 or wider. im not sure that will even fit in the swing arm.
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