Author Topic: GSXR Cams?  (Read 9113 times)

Offline El Gringo

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GSXR Cams?
« on: May 12, 2014, 01:25:56 PM »
Hi All

Had a quick search but couldn't find anything definitive.

I've got the chance of some cheap GSXR400 GK76a Cams - are these the ones that give the GK75 motor a bit of a lift?

Cheers

Chris

Offline greg737

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Re: GSXR Cams?
« Reply #1 on: May 12, 2014, 03:27:00 PM »
You should do some research to find out about the specs on those cams.  Suzuki is pretty good about publishing all the relevant bits of data.

Here's what the Bandit 400 service manual says about the difference between the 1992 and 1993 models.

Valve Lift:
1992 model                                         
Intake: 7.6mm (0.30 inch)
Exhaust: 7.0mm (0.28 inch)

1993 model
Intake: 6.2mm (0.24 inch)
Exhaust: 6.2mm (0.24 inch)

Cam Height:
1992 model
Intake: 33.134-33.174mm
Exhaust: 32.839-32.879mm

1993 model
Intake: 32.222-32.278mm
Exhaust: 32.372-32.428mm

If the dimensions on those GK76a cams are any greater than the 1992 Bandit 400 model you'll need the valve springs that were used on the GK76a.

Offline El Gringo

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Re: GSXR Cams?
« Reply #2 on: May 12, 2014, 06:02:37 PM »
Mines an 89 Greg, but i've got the genuine workshop manual so i shall have a look at the specs.

I'm sure i've seen a GK76 manual online somewhere.

I may just get Kent cams to re grind them as and when i do the engine or i might speak to Cross Customs in the UK about doing the motor for me, they run the bores 7mm oversize on their GSXR500 drag engines.

I need to concentrate on getting it into one piece first  :bandit:

Offline El Gringo

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Re: GSXR Cams?
« Reply #3 on: May 13, 2014, 05:21:26 AM »
Just found one of GSXR400Racers old threads

B4 stock cams
Intake lobe height 32.84mm
exhaust lobe height 32.54mm

Gsxr 400 stock cams
Intake 33.10mm
exhaust 32.75mm

Offline greg737

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Re: GSXR Cams?
« Reply #4 on: May 14, 2014, 01:57:37 PM »
I think it's worth stepping back and taking a broad-perspective view of the GSXR400 and Bandit 400.

As far as I can determine (from researching these 400cc bikes on the interwebs) they were never involved in a factory-supported racing effort.  While many of the design features that went into the GSXR's construction were actually developed on Suzuki racing motorcycles, there was no ongoing factory engine development effort that centered on racing a motorcycle with this 400cc engine.  Instead, the GSXR400 and the Bandit 400 were just "volume-sales" models which were meant to contribute to the manufacturer's bottom line profit and this situation even includes the very racy-looking Special Performance (SP) models of the GSXR400.

I'm not saying that GSXR400s weren't raced, because they obviously were raced by non-factory teams (human beings will race anything that moves), and it seems that the GSXR400 was the cream of the crop when 400s were raced because it was lightweight and could be modified with aftermarket parts to produce 67 hp.

But the specifications for a stock, right off the assembly line GSXR400 were focused on meeting other criteria with the major guiding force in GSXR400 and Bandit 400 engine design being the Japanese 3-tiered motorcycle licensing system, which imposed a 59 hp limit for engines up to 400cc (which is why the GSXR400 and Bandit 400 engine is actually 398cc).

It was the necessity of adhering to this 59 hp limit that kept the factory-spec, stock GSXR400's engine internal parts in a pretty static state until the limit was revised down to 53 hp which caused the 1993 models to be de-tuned (mostly by reducing the camshaft profile).

Bottom line: what I'm trying to point out is that pre-1993 GSXR400s and Bandit 400s all came off the production line with camshafts designed to meet the 59 hp limit (I'm sure there were was probably an allowable plus or minus horsepower factor that the Japanese government might have allowed and Suzuki might have exploited that, but nothing too extreme). 

So there may be some very minor variation in the camshaft profile (tiny differences in lift or duration), but overall they were set up for 59 hp.

If you wanted to make a real, noticeable difference in the Bandit's engine with a camshaft change you'd probably have to find aftermarket performance camshafts (plus some really high-quality springs to keep the new camshafts from floating the valves at high rpm).

« Last Edit: May 14, 2014, 02:07:14 PM by greg737 »

Offline El Gringo

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Re: GSXR Cams?
« Reply #5 on: May 14, 2014, 04:10:57 PM »
I fully agree with all that Greg, as you say a minimal cam change isn't going to make a huge difference.

At present i'm just throwing ideas around out loud (rather than in my head where the voices are) on the interwebs

I've got a bit of experience with tuning, especially Honda 400s and GSXR1000s so i appreciate the steps to be taken.

We'll see what happens but cams and a head skim/gas flow may be in order later on.

To my mind, rather than "why bother with a 400" its "why not go for it with a 400"

I find 400s to be the perfect thing for the road in the UK

Offline greg737

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Re: GSXR Cams?
« Reply #6 on: May 14, 2014, 10:37:12 PM »
That's why I'm here.  I'm quite satisfied with the 53 hp that my 1993 Bandit has to offer.  I'm pushing 50 years old now and my ego doesn't require that I have the biggest or fastest bike on the block.

My other motorcycle is a 2005 Kawasaki EX-250 which has only 28.5 hp.

The EX-250 is a lot of fun to ride, very light and high revving.  The biggest upside of the EX-250, in my opinion, is that you can ride the hell out of it without attracting too much attention from the police or risking your life at 100+ mph speeds. 

My only gripe with the EX-250 has always been that it's a 2 cylinder engine.  Simple as that.  It's a bit hard to explain but when you ride the EX-250 for a while you always end up wishing it had a 4 cylinder engine. 

A large part of this feeling probably comes from the fact that a 2 cylinder parallel twin with a flat-plane crankshaft just doesn't sound good.  The exhaust note is all wrong because it fires cylinder #1 then cylinder #2 just 180 degrees apart.  Then there's nothing for the remaining 540 degrees of engine rotation.  It results in a flat, farty-sounding exhaust note. 

 

Offline El Gringo

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Re: GSXR Cams?
« Reply #7 on: May 15, 2014, 11:55:10 AM »
Spot on Greg, pushing on a bit on a small bike is much more fun than having a big bike make life difficult.

I've not ridden an EX250 but i can imagine the noise

Offline TJS

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Re: GSXR Cams?
« Reply #8 on: May 20, 2014, 12:37:12 AM »
70hp is possible with these motors on 102 and 108 octane. My silver bike I've posted on here pushed around 68-72 depending on carbs I was using. I had CV carbs.
You will need $$$
lighter crank
1mm piston kit
skim head,  "supersport head job"
degreed cam sprockets
Wanted FCRs!!!
More Bandit 400 stuff on my youtube:
https://youtube.com/c/StanleysGarage369

Offline El Gringo

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Re: GSXR Cams?
« Reply #9 on: May 20, 2014, 04:57:38 AM »
Thanks TJS,

I'll start by getting it running first then probably look at tearing the motor down to see whats what. Probably a light skim and flowed head for the road - i don't want to get carried away just yet

This links to an article on the Cross Customs GSXR dragbikes

http://www.flat-out.com/post/SWEATING-THE-SMALL-STUFF2


Offline TJS

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Re: GSXR Cams?
« Reply #10 on: May 20, 2014, 01:19:56 PM »
More Bandit 400 stuff on my youtube:
https://youtube.com/c/StanleysGarage369

Offline TJS

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Re: GSXR Cams?
« Reply #11 on: May 20, 2014, 02:12:08 PM »
More Bandit 400 stuff on my youtube:
https://youtube.com/c/StanleysGarage369

Offline El Gringo

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Re: GSXR Cams?
« Reply #12 on: May 22, 2014, 07:17:28 AM »
Thanks TJS

Just had an email back from Kent Cams in the UK, £190+VAT for a fast road regrind, 10 days turn around + shipping time and ok for use with stock valve springs.

Waiting on a reply from Piper Cams as well to see what they say