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another jetting thread and cam timing


VJ

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Just put my gsx11g rat on the dyno, its got a homemade 4-2-1 freeflow pipe, ramair filters on bst36 cvs and powerscreen cams dialed in at 106/106 centres.

 

bottom end fueling is ok but after 4.5k it creeps up to 17:1 and then leans out even more up to 18/19:1. Im running 125 main jets at the moment, anyone know what size i need to bring it down to the 13:1 or so i need for peak power?

 

Im thinking of swinging past allens performance for some jetting tomorrow or sunday and picking their brains over the dyno sheet ive got here.

Edited by VJ
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I'd look at putting more like 144-155 main jets in.

Miss W. on her gsxr1100 with 36mm carbs, K&N pod filters and cobra zorst with open can, is running 150 main jets, V&M jetted it years ago with the standard Cobra can with 144 main jets but when we put the more open can on it was a bit restricted at top so the 150 mains went i  and it now runs very nice :)

My Kat 1127 f motor with 38mm carbs, K&N pods and gsxr1000k1 down pipes and open can is running 155 main jets.:)

Hope this helps.

Edited by wraith
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150s made a hell of a difference :pimp:

 

It powered through to redline now with only minor stuttering at around 5k so im hoping its about there. Its going to have another dyno run tomorrow and Im taking enough tools to pull carbs and adjust needles/float height/pilot screws whilst im sat in the car park so with a bit of luck i'll have it properly dialed in :)

  • Like 2
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Best run of the day here. Im very pleased with how smooth the air fuel ratio is given its running on pods. The ammount of power and the peak of it is baffling me though.

 

Ive got 106/106 cam timing on powerscreen cams so surely it should be higher in the rpm range being advanced over stock. Also i seem to be missing around 40/50 horses. Id expect a discrepancy from manufacturers bullshit claim to actual dyno run with shaft loss but still thats a fair bit lower than expected. Compression is around 175 on all 4 and the ignition system is faultless.

 

20180610_130255.jpg

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Its a gsx1100g (1127) with powerscreen cams, bst36ss and ramair socks, the fueling is good on the line, the compression is good and there is no ignition breakdown.

 

So why the hell am i not getting 125ish bhp and 100nm?   I think i need to rework my cam timing quite seriously. stock powerscreen is 104/103 timing so I really dont see how 106/106 kills the top end so much, if anything i was expecting it to be a bit flat at low revs and a bit more peaky at high rpm.

 

Thinking about it: if my inlet is 2 degrees advanced over stock and my exhaust is 3 degrees over stock and this is whats causing the power loss.... If i put my slotted backplate in and give it 5 degrees of ignition advance would that solve it? or would that add more confusion as the cams are still advanced over the crank?

 

Cheers

John

Edited by VJ
ignition advancer waffling
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It's peaking early. but doesn't fall away completely after... what ignitor box are you using ? - although power peaks early it's revving to just over 11k - GSXR1127s hit the rev limiter at around 10,800 (true revs) ….. dunno what's happening.

What's your exhaust like ?  - even a poor design shouldn't kill the output that much .

It's not like your bike is making loads of bottom end and losing at the top …. it looks like a 750 Inazuma  dyno run, or Swiss market bike - it does look like one or two things are restricting it VJ.

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52 minutes ago, VJ said:

Its a gsx1100g (1127) with powerscreen cams, bst36ss and ramair socks, 

 

Yes, just saying my old 2v GS1000 put more out, so yes I would also expect your 1127 GSX1100g 4v to be putting out a lot more ;)

If it was me, I'd forget about any advance on the cams etc just put them in at a standard TDC (which with slotted sprockets you can get it bang on ) that will give you a starting point and when you know you're getting the top end/bhp you're looking for you can start playing with the advance from there.

Always good to have a good starting point you know is weight :)

Quote

 

 

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7 minutes ago, Oilyspanner said:

It's peaking early. but doesn't fall away completely after... what ignitor box are you using ? - although power peaks early it's revving to just over 11k - GSXR1127s hit the rev limiter at around 10,800 (true revs) ….. dunno what's happening.

What's your exhaust like ?  - even a poor design shouldn't kill the output that much .

It's not like your bike is making loads of bottom end and losing at the top …. it looks like a 750 Inazuma  dyno run, or Swiss market bike - it does look like one or two things are restricting it VJ.

Its got the stock GSX1100G ignition box on it, seems happy to pull through but obviously its dying off before redline.   exhaust is a homemade 4/2/1 with a open slash cut on the end.

 

@wraithi think your right, i should take it slowly one step at a time and put stock cam timing back in and see how it goes from that, i just find it hard to believe that im so down on power for just a couple of degrees.

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I know how your thinking, did all this when I built a GS1000 tuned motor, had the works in it played about with the Anderson S3 cams with the advance to see what it did to the power output and where, its came as a surprise at how much a couple of degree can make to a engines out put.

Some will say it's the zorst you have in but 4-2-1 is the best for all over power, yes there is tuned length that can fuck the hole thing up, but I've never had a real problem with it, ( well maybe once on a old cb750 with a car end can and that would not rev all the way up, but I think it was more down to carbs on that as they have 2 main jets :o and a pain to work onxD bloody hondas)

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yeah, it is a bit of a shock.

Its a homemade 4-2-1  using a bit of car exhaust and a set of zxr750 downpipes that i cut and MIG'd because nothing else fits thanks to the frame and engine combination but i did try my best to make it as smooth flowing as possible..

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Have you had this engine running strongly before VJ ?  or has the power only been less than great after this rebuild ? - I remember you had a piston/valve coming together on first build, did you use a GSX750F head on this or the 1100G one ? - trying to spot something for you … it's great when all works a treat but an utter pain in the arse when your hard work seems for nowt.

My last big project was fitting a big bore kit, flowing the head and setting the cams etc - one problem I did find was that when I tightened the cam sprocket bolts, the sprocket moved - caused about 3 degrees of error - had to do them twice. 

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No thisis a fresh build using all gsx1100g parts apart from the powerscreen cams, my dot head suffered 2 cracked guides so that is underthe bench awaiting refurb.

I think i checked my timing after thread locking the sprocket bolts,  ill check before i adjust the timing. Its going to have to wait until the weekend though now because i need it rideable for work. Ordered a proper degree wheel too not a 100mm diameter protractor.

 

Cheers 

John 

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be interesting to see what fix's this - thanks for posting, going to learn something here :tu - if you follow the graph through to what you'd expect peak HP @rpm then you can see a reasonable output - to me its like its hitting a restriction / limiter

you don't happen to have a restricted set of carbs preventing full lift ? - or maybe you need softer lift springs - i.e. dynajet kit setup - dunno ??? - i've got a set of 36's part dyna worked if you want to try them - i.e. borrow

 

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The cams measure within service limit for lobe and base circle combined measurements so i think thats ok, doesnt rule out a sharper grind taking the duration away mind.

 

Slides lift ok when i look in the back and give it a handful. What does a restricted carb top look like? These look totally stock tbh i cant see any non manufacturer quality bodges in there.

 

Cheers 

John 

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