My built xj 750

So i finished my xj build. I got the motor back in and timed and it runs like a boss. I do recommend doing a 4-1 pipe and then pods. I don't care what anybody says it iis a good mod. I am going monday morning to have my bike dino tested, i predict around 100-105hp, top speed 135-140. All pbatained by running the proper jets,pods,and a open header. Oh and 20-50 oil. That is it no cams yet, only cuz i cant find any hot cams for this bike or for that matter a big bore kit. but i can assure you when i do im buying it. Pics to come in a few days i don't want to upload them until my new bars get here in the mail.

I will be more than happy to give you my jetting info. its not a black art as people say, just common sense and a lil mathematics/science skill.

 

Not trying to burst your bubble you have not said what mods you have. Numbers seem very high. My built vmax only put 124 rwhp. Tell us your mods sounds like you even have stock exhaust. No one makes performance parts for an xj. If you found a big bore kit its rare. The reason i say your numbers are high stock rwhp is maybe 70 to make 30-35 more on a 750cc motorcycle is gonna be hard. You say 135-140 top speed thats about 10500 to 11k rpm. getting kinda high isn't it. But i could be wrong when you get your dyno slip post it here is mine. Didn't you mean dyno tested?

 

Yes i did mean dyno, burt my numbers aren't high. I the 1982 xj 750 seca puys out 86 hp at the rear wheel stock.My mods are simple bolt on stuff pretty much just regualr air pods from china, a vance and hines 4into1 pipe dumps out at the header proper jets, proper timing, good 93 octane gas and race oil. Oh and i drilled a couple extra holes in the crank shaft. But i haven't even sahved the heads yet or put new rings in yet. And i am still tryuing to find diferent shaft gears to try and change up the gearing alil bit

 

When will the wake for your engine be?

 

Hush now. Could even happen on the dyno. I'm waiting to see that printout.

 

about 10 minutes after the Dyno I imagine.

 

with 4-1 with jets and pods I'm gonna bet it'll be 90hp

 

You people are just jelly that someone who is smarter than you tuned his xj and made it faster than yours. These inline fours are tanks my old 87 honda hurricane 1000 in4 used to do 148 every day with me on it by only dropping two teeth in the back sprocket. IO sold it to my buddy last year and he still rides it every day 148 mph ewvery day inline 4's are tanks.

A smart person on here would ask for advise and tips on how i made mine faster, i am not going to blow the motor why would i. I am pretty good with bikes.

 

Do you have any paperwork with which you can back up your claims? Timeslips? Speeding tickets perhaps?

I find it amusing that you made your Hurricane go nearly 20 MPH slower than it did when it left the factory.

 

I just peed a little

 

seca 750 run 62 to 68 thats a yamaha crank horsepower claim. A 79 cbx makes 82 on a dyno a suzuki 4 valve per cyl gs1100 makes 85rwhp and they show them making 100hp If a seca 750 made that much rwhp it would out run a gs1100. fj1100 makes 100 on a dyno. Heck a honda cbr900rr fireblade makes 103. All i ask is post your dyno slip when its done. I have a feeling that we will never see it .
And why in the world would you drill extra holes in the crankshaft the holes are for balancing If your trying to say you lightened the crank that is not how you do it .

 

Umm, who puts their big end caps on backwards and then whacks the engine with a hammer to make it turn, takes 3(?) goes to time his cams and drills his crankshaft??? :? How does a 4 into one exit at the headers? That's 4 into 4... What brand of Chinky pods did you use?

Post your dyno sheet (real one, not a doctored/'shopped one) like others have said :lol:

Lets have some details on how you balanced that crank, static/dynamic, with rods/minus rods, what weight did you use? :wink:

 

Have you got the dyno-saur sheet yet? I'm genuinely interested to know what the motor made & how it felt on the rollers...

 

i give no validation to anyone who uses the term "like a boss"

 

Just another thing (then I'll shuddup about it I promise lol ) but seeing as you can modify your own crank, why is finding hot cams such a problem? Why not take a couple mm grind off the base circle of the stockers for more lift & reprofile them for longer duration?

 

It's the race oil

 

Why so negative everyone? Give the guy a break! One of my favorite things about this site has always been the sense of community and positivity. I've bailed on other forums that are full of people that just look for a reason to bash every post that comes up & I really hope that doesn't happen here.

Take it easy guys, you're making us look bad!

I say post what ya' got dude! For cryin' out loud let's see some pics & maybe the dyno slip if you get around to it!

 

I just stumbled in here seeing whats going on I'm all for dyno runs because its actually proof but I gotta say, some are going to say doing things like drilling out crankshafts are a bad thing, some will say its a good thing.

I will say if you aren't worried about blowing it up, you're doing it wrong.

also, pics!

 

All I know is that if people are going to make extraordinary claims, they need to also provide extraordinary evidence. Ideally both need to occur at the same time. I really do want to see the results.

That statement could be read either way. Do you mean "Balls out" (not those balls, look it up.) or do you mean to build conservatively so you don't end up with ah steaming heap?
When it's my money going into the build I will only go with the "balls out" methodology when there is more money to be won.

 

What I mean is these ideas arent so new. back in the day people were doing all sorts of crazy things to pick up an rpm here and there, they were all worried about blowing it up. If you have gotten to the point of taking a drill to the crankshaft and are NOT worried about bad things happening, then you aren't doing it right. the very nature of mods like these risks blowing stuff up.

I'm not here to hate on the guy some guys myself included just feel the need to push the envelope but you can't just write it off because you're "good with bikes".

also, again, pics!

 

just a observation but look at the last several posts buy Mr. Crank Driller. now does this seem like a man who knows how, where or how big of a hole to drill in a crankshaft ?

 

that's why i want pics of said crankshaft :wink:

 

four into one...pods..complete tune and race prepped carbs...i'm with you man.. push that little bugger to its limits...how do you know your there?? you'll start doing things like twisting your drive shaft in half..but don't worry that's not a bad thing it just means you did it right
don't forget to get the best clutch you can afford too it doesn't do any good to have extra power when your slipping a 30 year old clutch. :wink:

 

YOU know what i did dyno it, and i didn't get what i wanted but im still in the tripple digits, which i can guarantee is faster than any of your xj's. And as to the idea of me posting my slips, thats a big fat no. Why would i want my competition knowing what i got in my bike. HaahA thats crazy, I really do not care if a few random people on a forum don't believe me. I will post a short video of my bike idling. So you can recognize what just flew past you at 140

 

Cool. I'd like to see the chart. How much did your changes effect the midrange?

You are also a "random person." Your competition isn't going to know who you are if you post up time slips without a name.

 

its cool you got 100+ hp, if its a street bike then your only competition is the guy with the radar gun.

not that I didn't believe you could do it, we're just raggin on ya for drilling your crank.

 

Just this week we ran a Harley that had four pounds removed from the crank on the dyno and it was crazy how fast that thing would rev up.. you might not gain big numbers from lightening the crank but dam it gets there fast you just have to remember its going to deaccel just as quick :wink:

 

that sort of mod would be left for strictly a race bike right?

 

OK, so why would you post what you expected to see & are aiming for if you don't want "the competition" to know?

As Krafty said, it's not about us believing/disbelieving you can do it (personally I hope you can, pushing the limits is good) but some proof would be good since otherwise all you have are numbers you could've pulled out your butt... From some of the mistakes made in the initial build it does sound like you may lack the experience required to drill a crank effectively/safely but if I'm wrong fair play to ya.

like I said, if you can do that why are you worried about finding hot cams when you could do a base circle grind & reprofile them? you must have the equipment as most of it is also required to modify crankshafts. (or you could look into the 750E-II head. big valve head & lumpier cams)

 

stevo32 sounds a lot like a snake oil salesman. Lots of claims and no proof of content. Really sounds like a little kid needing attention. I think this thread needs to die unless he can come up with proof. And he's welcome to come up to my place anytime and I'll put his engine to the test for him!!!

 

This whole thread has me rolling on the floor. Keep it up! I'm definitely not seeing any pudding for the proof to reside in.

 

Well, then there's this, to answer the drilling question...

Smarter than all ya'll!

 

So im still confused as to why its a bad thing to drill your crank out to lighten it up a bit. People have been doing that for ages. Just a part of getting those precious R's. I really don't want to blow my engine up. But hey if happens it happens i wasn't alive in the 80's i don't know what people where doing to these bikes, i would be willing to bet nothing, i would assume they would be tuning kz750's/100's andf zr's i really couldn't telll ya. But if it does blow up then thats when i know that this mule of an engine can't take any more

 

knowledge is power, and you ain't gots none

 

There is nothing wrong with drilling a crank to reduce the rotating mass of an engine, but it's a technical process. The machinist (I used that word for a reason) doing the work must be aware of the type and hardness of steel that was used to build the crank; how to figure the size, number, and spacing of the holes to be drilled; how to alter the pistons and rods so the rotating assembly comes back into balance; and re heat-treat the drilled crank once the machine work is done. Skipping any of those steps will ultimately result in crank failure (though the heat treatment can be skipped if the proper drilling technique is used, and the crank material is suitable). Every time a piece of metal is worked, new stress risers are introduced into the piece. Those stress risers MUST be dealt with appropriately, unless your intent is to make scrap.

Pop quiz (open book, provide a link if you had to look it up):

How does one go about figuring bob weight?

 

THIS is the point everyone is trying to make.

You don't just willy-nilly drill some extra holes in your crank cheeks, you'll horribly imbalance the crank. Any additional balance holes in the crank HAVE TO BE offset by corresponding reductions in rod and piston mass to bring the whole rotating assembly back into balance.

If all you did was to drill a few new holes in your crank cheeks and button 'er back up, you've basically ruined the motor.

How long it takes it to shake itself apart is not something you want a dynamometer operator to discover for you (he'd be a bit upset when your grenade makes a mess of his dyno room.)

 

He didn't do it (see my above post) so the bike has been run with this mod already by PO.

Perhaps the PO or his mechanic was an expert who did it right. Time will tell.

 

hm... i still think he's too scared to post the dyno sheet cause i'd call him up next time im in mad town to throw down - stock. hah.

 

I think that he may have further modified the crank.

Here is my philosophy on calling out when something looks to have been done incorrectly. Any owner can do whatever the hell they want to with their bike, however, a forum exists for the sharing of information. I would not be pleased if I followed someone's advice about modifying engine internals only to find out that the information given was either incomplete, or incorrect.

 

Still how u do it bolt on ain't that good even a Turbo hubusa yes I spelled that wrong I know. .. its besting 280 a boss hoss300 even the y2k bike Jay Leno has is just more then that and they are useing air plane and car motors. I'm not saying you can't but I think at 3000 Buck a horse plus feed for each horse you most have your whole body invested in it.... and as far as you don't want us to see because of you not wanting us to better you is a little kidish. I will love to see a horse drawn bike and video games don't counts. Just joke but really wow OK I said me peace but a drilled crank is risky. Love to hear that bike scream down the road or sorry na

 

that all well and good until it blows up on you're way to work or somewhere you NEED to be so you don't get fired or miss some monumental moment.

all cars trucks and bikes have been getting modded since they were invented.

so just maybe you should listen to some of these folks who have been, working on, fixing and modifying these bikes for twice as long as you've been alive.

But Hey what do we know.

 

Like I said, if you're that keen for performance look into the 29R head, it has bigger valves and hot cams (and 29R crank if/when you need one too, they're stroked 0.1mm over stock 750 )

Also just thought I'd add that next dyno run you may improve power by running better than 93 octane fuel (I believe that's what you said you'll be running).
My CB-1 engine runs similar output per litre to what you're aiming for at just under 150bhp/litre and there's a huge "seat of the pants" difference between running normal pump grade 95RON we have here and if I run BP 99RON .

Also, running higher octane juice will allow you to advance your timing a couple of degrees or so (has to be done via either modified pickup coil mounts or standalone programmable TCI but worth doing as done right it'll also show improvements)

 

This is just to funny. Says triple digits and won't post sheets. I cry fowl his triple digits are 64.3 or something like that. What ever he is smokin i want some. My v max made 105 stock and was much heavier. And my power numbers are right on compared to others. Granted we added another 20 by dyno tuning the hell out of it. Trust me i know your not gonna get triple digits out of a seca 750 not even with a good sniff of laughing gas. and when he is passing you on the streets of his mind at 140 he will only be spinning 10400 rpm. When he said he was running pods and no canister on the header. I knew he wouldn't post sheets. Don't get me wrong i am not putting anyone down. But i have been around dynos and racing over 35 years now

 

Depends which post you read, it's either open headers or a 4 into 1...

I still say he left the forum because he had to pawn his computer to pay for dyno cleanup & repairs when his crank let go & set the place on fire :lol:

I'd happily welcome him back & talk him through other upgrades like ignition advance & cam regrinding though if he wants to come & post dyno sheets & stop being such a prima donna. :roll: :lol:

 

When I went to dyno my 750 the dyno guy looked up the specs for it and came up with 82hp and said we would be lucky to see much over 50 at the wheel.

The dyno run is on the old engine before I built the 820cc big bore engine. Was with a 4 into 1 Mac system but no pods, and runs just like you would expect an XJ750 to run.



I am highly sceptical that adding pods will add another 40hp and get me to 100.

 

Pods will get you way more than 50 HP. You just have to get the right sort of pods. :twisted:

 

I realize the Threads old but it's right up My alley so I'm Posting lol. My main goal with My 82 750 Maxim is making it as quick as possible. It's My first attempt at building Power, but I've had some results, Here We go: Started with a Diet, dropped most of the weight upgrading the exhaust and Rear Shock's, but it's pretty much down to a frame and Motor now as well. I have a Mac 4 into 1 with a 10" straight pipe. I'm Running Pod's, but I took a Die grinder and opened em up around 10thou so they would fit the Factory Intake Boot's. It responded really well to that. And I jetted it out to #130..

 

I have no Dyno figure's, but I'm pretty much neck and neck with My buddies 13 650R to 100mph. Don't care to take it much higher than that, so I don't know the Top Speed. If I had to guess I'd say somewhere between 95-100hp at the Wheel. She's not the Fastest around, but it's suprised everyone that's taken it out, Shocked some lol.

 

I had my old 83 XJ650 Maxim up to close to 120mph, and had a bit more throttle to go, but I was already risking my life doing these speeds on grooved pavement with worn neck bearings.

Not sure about my 83 XJ750 Maxim. I'm about 20 uears older now and not as mich a risk taker on a 40 yr old bike that came out of 5 year storage this year

 

Here's a few Pick's, the first is without the new Shock's I just put in. The 2nd is the new stance with them. I still have a ways to go in the look's department, but Mechanically I think I'm about there.