Horsepower mods ? Cant find a tell all thread for the 750

I was just wondering. I think it is inevitable that after getting our bikes running fine and riding them for a while that the bug will bite some of us pretty hard. I have seen the fuel injection mod for about a grand and that looks beautiful but I never did come across the final hp gains or fuel economy.

Where are the gurus with the list of horsepower mods hiding at or is what you see what you get.

My first thought was a 3 angle valve job
est. price
hp gain-

port polish intake runners / carb bore
est. price
hp gain-

Gear swap for top end or low end ( My personal preference is a low end jump cuz I hardly ever go above 65)

weight reductions

big bore kit
size
cost
hp gains

cam swap
size
cost
hp gains

etc etc.

I dont know the ins and outs of this engine just yet but rest assured I will. I am going to the church of clean right now and to me the carbs are the most influential part of the power on these bikes. Love the site and everyone is so helpful now lets just top it off with this little cherry.

 

For the 750, I've heard that cams are available, for $400.00, flat-slide carbs have been talked about several time, about 40 LBS is shaved in a typical "bobber", gear swap is almost impossible without a full-on machine shop- unless you count the 8% taller gears from the 900, which is a drop-in.

My "Fantasy Mod" uses an Australian 892CC motor with pistons from the 400CC motor adapted in, giving about 950CC of displacement. Add some TURBO components and a custom Microsquirt, a wing-cut and balanced crank, stronger coils, nuts and bolts, it's looking like 160 HP all day long.

It also looks like a $7,000 budget with a resale value of $3,000

 

I got too looking at my cbr engine and thought to myself why couldnt you slap on an elbow and put the downdraft carbs and a fuel pump on this thing???

But I am an absolute rookie greenhorn when it comes to figuring out what exact carbs/CFM I would need ???

I have no qualms about doing something like a TBI swap off an old chevy etc etc. ls1 coils seem like a cool idea. EFI seems like a lot of engineering and moola.

I have ported and polished every single vehicle I have ever owned so I will be doing it to this one as well just wondering if there was an example anywhere. Please dont start with the whole smooth vs rough wall debate : )

What about a crank swap from say a cj650???dunno specs just doing a feeler with all of this.

I think that with any mod section price will be a huge factor for anyone so I agree a nine million dollar supercharger with nitrous and wheelie bars are prolly beyond the realm of this theoretical discussion haha. Thanks for the input. I sure would like to hear the resident machinist chime in on cam specs and power curves.

 

Some well priced big bore kits on ebay at the moment.

 

I had a honda cb 550 and the big bore deal with it was taking cb750 pistons and machining the crapola out of them removing lots of meat off the skirt removing a 15mm offset on the top of the piston complete dismantling of the engine and about 1900 bucks? Please tell me it is just a bore and slap larger pistons in??
what is the overbore size?? 820?

 

wow 130 bucks!!!! that is really awesome

 

Exactly my plans for my 900, the engine has 68,000km on it and is due for rebuild ... should yield a little closer to 1000cc ... an XJ1000 ... mmm that has a nice ring to it

I'm thinking I'll swap out the final drive from my 750 to the 900 so it will just accelerate like stink but have no top end. That extra 8% top end in the 750 will be lovely for those country cruises. Other than that it will be totally stock, and loving it.

But why for the love of all things shiny would you put 160hp in a bobber? Surely a fairing and some streamlining is what you need once you get over 80mph? If you want acceleration leave the final drive be, and just get the engine to run right, these 750's have buckets of power, and if you want top speed, get a different bike.

 

Doesn't the stock 750 run somewhere around 127mph on the top end? Where can you use more than that with a street bike?

The bottom line in regard to the shaft-driven XJs (or ANY XJs for that matter) is that Yamaha "built" these things right from the factory. They really are "racebikes for the street." TIME touched on the biggest drawback: cost. Or should I say, cost vs. gain.

You can drop WADS of cash to "up" the performance of an XJ motor; but unless you go whole-hog spare no expense crazy, you won't gain very much over stock. Yamaha has already taken the easy territory. BIG gains will be hard to come by; again cost effectiveness becomes a factor for the tiny gains.

Get the bike running properly and you'll be quite surprised at its performance I'll bet. By running "pods-n-pipes" you're "giving away" quite a bit of the stock performance; getting back as much as you can is a good place to start. And that can be done without a great deal of expense.

 

In the xjforever parts catalog there is some cam interchange info. Keep this forum posted, I would like to try my hand at port/polish. You can teach me. haha

 

Re: Horsepower mods ? Cant find a tell all thread for the 75

This guy offers cams http://www.megacyclecams.com/catalog/catalog.pdf

See page 63 and on... I don't know if anyone who hangs on this site has experience with them... I have selected part number 256-00 from this catalogue which is a mild upgrade -- and am in the midst of re-assembly of a rebuild of almost all components of my bike, but I won't have ignition til probably March. http://www.xjbikes.com/Forums/viewtopic ... art=0.html

I don't even know with certainty whether or not I can definitively report a difference, except "feel" - but I will report when I do
-- assuming given my skills it all works --

 

so looks like 450 for a cam swap and 300 for pistons.
hp gain unknown but for a theoretical moderate power increase\
750 doesnt sound bad at all on top of the 600 running bike purchase price.

 

If you call him (at Megacycle) you may get a better deal also watch ebay -- I got mine as a whole separate set of cams (I did not turn in my originals for machining) for $300 shipped.

I am not connected w/Megacycle in any way and I am not endorsing his products nor do I even have my bike running yet...

 

Do you suppose the power would be noticed with a big bore. The ebay listing said comparable to stock (compression) just bigger outer diameter. Also I wonder what brand they are. If they are legit, and not melt down after 500 miles.

 

ever heard the age old addage...there is no replacement for displacement??
almost 11% larger displacement. should be a nice kick in the pants.

anybody here that has done the swap and a dyno run?

 

Oh yes, I am a firm believer in that saying, I am a street rodder, nothing like a big block. Haha, I am probably going to do it, I stopped by my machinist earlier today and thought boring it would be about 100, don't know if thats high, but he does all my motor work, and my customers. I trust him.

The only thing that worries me is cheap pistons getting melted. And I wish they had more compression.

 

can you deck the head on these things?

 

Dang, didn't think of that, I am going to inquire that when/if I take my parts down.

 

I would pay a hundred bucks. that is why I figured about 300 for the pistons bore and chamfer for the ring run in. and maybe a decking of the head or block

 

Just looked it up, stock compression is 9.2, that isn't bad really

 

I heard you can get pistons from the xj900rk? but no idea what that will resize it to?

cant find em though

 

American 900's are only 853CC and combined with a 748CC motor only gives about an 800 or so. You would need good pistons and the cylinder block they came in, and I don't even know which rods, but I've heard that getting rod bearings is a "Witch"

Since these motors are all aluminum, the compression should be able to go up to 11.5:1 on 93 Premium and there's a formula for calculating the horsepower increase (somewhere) but this moves the TIMING on an XJ, and you will need a degree wheel and a dial micrometer to re-set the cams. (measure twice, cut once).

----------------------

A related point - an engine is an air pump, and a Yamaha 750 is a well thought out air pump that was #1 in the world in 1/4 mile times AND met emissions standards AND had shaft drive AND self-cancelling turn signals!!

By comparison, a 350 Chevy (1981) in a Camaro would need to make 625 HORSEPOWER and still pass emissions !! That's NASCAR territory, and you're not going to just throw parts at it and make it better. You would need a carefully thought out approach. (hopefully not a rant :wink: )

 

Re: Horsepower mods ? Cant find a tell all thread for the 75

I asked the seller a question and those pistons are made in taiwan and are cast...
who is gonna be the guinnea pig?

I ordered a new starter and dunno what I am gonna do till it comes in. aaaarrrrgh. lol guess I could look at makin a seat pan

 

That sounds sketchy, where would you get another head gasket if you need one. Not sure I want to be the guinea pig. However dang tempting.

@time- #1 in 750 class 1/4 mile time, in 1982? Can't beleive it was the fastest bike made in 82.

 

I've seen this kind of debate so many times it just gets boring after a while ... "Where do I buy some bits that will give me bolt-on horsepower?"

We have magazines dedicated to selling trinkets to this market here in Oz ... and the traders make a lot of money out of the "Fast Fours" and "Street Machine" readers who buy shiny new stuff they can show off to their mates.

Actual performance data and figures from dyno and track testing using a structured engineering test method are curiously absent ... I wonder why?

 

I 100% agree. where is the data from the guy who put a turbo on a non turbo seca?
or the guy who has done a piston swap?
or the port and polish
or the cam swaps or the fuel injection with some kind of solid numbers.
The honda forums I was on prior to this had so many numbers and data it would make your brain go numb. Am I going to have to blaze a trail here and learn to machine and advanced physics lol

 

Not really a lot of guys who want to soup up the xj on this forum, the attitude since I've been on here has been if you want to go faster buy a bigger bike.

 

Very few enthusiasts have unlimited free access to a dyno. These XJ's weren't popular as racing bikes so they haven't been modded much for the track, unlike other makes and models you'll find lots of data for. If you want to spend a bunch of time, trouble and expense researching and gathering data I'm sure it will be well received and enthusiastically debated.

The comments regarding caution are well-intentioned and are trying to save you wasting a lot of money and time for not a lot of gain. These were the fastest bike in their class as built and the Yammy engineers knew what they were doing. But hey, it's your money and time so spend it how you see fit.

 

I have a dyno shop very local to me here on the coast. I plan on getting her running and safe and legal over the week and then talking to him about multiple dyno pulls.
My first plans are to run bone stock for a baseline then
port and polish first and foremost.
then....
Whatever is available funding provided. either a piston kit or forced induction.
followed by a cam swap.

 

problem is I dont have a tach and I am using the simplified wiring harness. I wonder how much of a factor that would be in a dyno run and is there a temporary way to put a tach on it.

 

Use a Laser Digital Tach.

Pull the Crank Cover exposing the Rotor.
Affix a thin Reflective Strip to the Rotor.
(Clear Nail Polish will permanently anchor it)

Set Hand-held unit for appropriate scale in rpm's.
(0 - 10,000 rpms) most likely.

Aim Laser at Strip.
Digital read-out.

No wires needed.

 

awesome. just a plain ole good idea. that will even help with setting idle

 

I've seen these used but haven't tried one:

http://www.ebay.com/itm/DIGITAL-TACHOME ... 484339d4cb

The dyno will have an rpm pickup on it so it won't be an issue if that's all you need it for. After the test they'll give you a printout or data file with the test points on it. Anything you put on there won't be any use in a sweep run because it will be changing so fast you won't get a reading.

You might like to start a new thread under the XJ Mods Forum with a test plan similar to what you have just mentioned but in more detail and then reporting the data back as it progresses?

 

I'd be cautious about cast pistons in a high performance engine....maybe Wossner makes a set you can use? I've bought 2 sets of pistons for other bikes and they are forged and look like works of art. It's almost a shame to hide them inside the engine! I know they have a pretty full selection now so you might want to look them up. I can hook you up with the # of the US rep if you need it, might save you some bucks.

jeff

 

One thing you have to remember when doing the mods port and polish big carbs ect. You will loose low end drive ability it will make more power up top but at the sacrifice of low end power where you normally drive. The big bore kit would help this. I think you will find that the factory did a pretty good job in terms of drive ability and performance combination. Just remember these bikes were designed over 30 years ago. Engine technologies have come a long ways since then.

 

Before you fully commit to your Horsepower project; I'd urge you to read a couple of the articles from those who've gone before you.

There isn't much room left to grow before you start experiencing problems that develop due to the limitations of the plant.

Increased compression ratios cause Head Gasket problems and leaks.
Do to the electronically controlled advance; what you're likely to gain at top-end might get lost in idle or getting out-of-the-hole.

The Bootlegged materials included on the infamous CD-Set might very-well have the articles that appeared concerning Race-preps and H-P Mods.

 

I still say get it running right and RIDE it; although you might want to fit a tach. Your "seat of the pants" will have you shifting just when the going gets good; the fun part of these motors is from 6K to 9500 which SOUNDS like it's getting wound way too tight.

You may discover that it has plenty of performance without dumping $$$ into it.

 

Wow. cant find a set of big bore pistons anywhere....Might buy one piston off of feebay just so I can mic it out and see if there is something out there that will interchange.
Anybody have any ideas??? bueller?? haha

 

wiseco will custom buid custom pistons but has a minimum order of x amount of sets

 

yeah I was lookin at that but geez. I think I will just keep y 650 bux. I am pretty darn thrifty though. I know now the sr185 has the same size pistons diameter wise but there are just a couple of other measurements that might prove necessary.

It just seems as if these are some pretty dang rare bikes. for any parts.
will hear back 2morrow about the dyno pulls.

what about an entire engine swap? does anyone know if or what year 900 will fit in? 1100-1200? I am totally new to yamaha so bear with me please if my questions sound dumb.

I have shoehorned a cbr 600 into a 76 cb550 before so I have no fear.

 

I have just bored my spare 750 engine to suit a Wiseco big bore kit, and I have collected a Yoshimura big bore kit as well. The Wiseco are forged but the Yoshis are cast.

There will be a Dyno run at some stage when I set up the EFI. I seem to be a bit slack getting things finished at the moment.

 

Well I hear stories of the revered yoshi pistons but did not know they were cast. I dont see why cast wont work but it just seems scary to me. plus about 300 bux difference.

which ones are you planning on using??

 

Re: Horsepower mods ? Cant find a tell all thread for the 75

When I owned my XJ900 back in 2000, I once left a stop light the same time as a new CBR600 and we both went for it. I leaned on my bike hard but he left me for dead. How much faster is a new CBR600? Dunno, but if you really want more power I'd recommend buying any number of newer motorcycles that have come and gone in the intervening 30 years since your bike was built. Hot-rodding old bikes only makes sense if there is an excellent parts support network and large tuning potential (KZ, GS, GSXR etc). Even then, you are left with the usual high perf woes like over heating, pinging, adding octane booster, clutch slip, transmission worries etc, so that it really only makes sense for a race bike or drag bike. Even popular hot rods like the GS are getting harder to find parts for. I put a lot of money into an XJ Turbo a few years ago just to fix the infamous starter clutch and it definitely wasn't worth it. Ride it for what it is and sell it on if you need more. I'm not sure how thrashworthy this engine is anyway, as there seemed to be a spate of Maxim X's trashing their bottom ends in completely stock trim a few years back.

 

No, primarily performance parts or any "deep" engine rebuild parts.

This is what more than one of us has been trying to explain. The Seca 750 (or any big-bore XJ, for that matter except maybe the 1100) was NOT popular as a racebike, dragbike, or any sort of "hotrod" back in the day.

You're not finding "hotrod" parts for the XJs because there never was any demand for the markets to respond to; not then, not now.

They simply aren't out there. Finding STOCK "deep engine" rebuild parts is difficult enough (again, very little demand.)

 

well I started to soften my hard head today. I figure I will get plenty of kicks for an 800 dollar or less bike. Im gonna make it pretty and ride the fire out of it. started my seat pan today.
I hate the cookie cutter look of todays bikes. I wanna go fast and for cheap. I see 2002 bikes for 5500 bux. That is outrageous imo. Guess I could save up and get a big boy bike in about 10 years hahaha. I still think Im gonna be a sexy beast on my SECA.


next up for major mods: port and polish..

 

In the early days of hot rodding anything there were no "kits" for performance either. People did what they could with what they had available. I believe in this ideal as well. Ya buy a bigger, newer, faster, bike and be like every body else, negative negative negative. I get annoyed at closed minded people trying to close others minds. I say poppycock, and good day. My search to hot rod any and all of my vehicles will continue on with or without positive or negative comments from anyone viral or face to face. As should anyone elses search.

Seat cowl looks good

 

I believe in cheap horsepower. these things are toys and I like to tinker. I would like to ride it though and if there are no easy outs then it wont last long in my stable. I might just pony up and slap a hyabusa engine in this frame. mwuhahahaha.

seriously though, I know it will never be a world beater but it will beat the next guys xj.

 

Wisecos.

Cast are fine anyway, that's what the factory pistons are.

 

Any word on how often some good pistons show up???
I saw some on ebay that were 818cc but would that extra 2cc really make a huge diff other than peace of mind being forged?

 

Took me a 18 months of looking to find the first set, then ended up with 3 sets.

One set was second oversize OEM complete with barrels already bored out to suit. Sold those to a XJbikes member.

 

Re: Horsepower mods ? Cant find a tell all thread for the 75

I agree with you these bikes were fast in their day but compared to todays bikes they are sleds. I would just drive it. If you want to go fast buy a newer sport bike. You love to tinker buy a kz 1000 or gs 1100 parts are everywhere for them. And the parts are proven to work. You wouldn't be guessing what would work or what wouldnt. I do admire the fact your putting the time to make your bike the way you want it. From what i built and done to bikes the past 30 years all the mods your wanting to do will pick up maybe 10 to 15 hp if its all sorted out and everything works correctly. Like people were saying carbs and big bore kit pipe plus all your labor which i know is free your looking at almost 2k you must really love your xj a lot to put that kind of time and money into a 1k bike . The 1k is what kbb says they are worth i know to most of us they are worth more.