gs 400 vs 425 camshafts

[Guest]

Does anyone know if the gs 400 and 425 cams are the same??? I cant find any info on them anywhere.

Looking to get some hot cams for my gs 400 big bore cafe project. Megacycle has cams for 425, 450 and 500 twins but am not sure if they will work

[derwood]

I think all the 400's I have seen are 8 valve, with rocker arms. so they would not be the same.

[bogmonster]

Thanks

Thats exactly what i was looking for, thanks for the help!!! I will give Megacycle a call today and get their input.

Big bore, high Compression pistons, good valve job and now some hot cams...... should be a fun bike!!

[Mekanix]

There are gs400 A B and C model engines.
The C model has highest lift of the 3.

You could use the GS500 cams if they fit lengthwise. Or have them made to your specs.

Web cams reground mine for an extra 100 thou lift.

Yours would be easier since they are symmetrical whereas the 8 valve with rockers require an Asymmetrical design.

What is the current lift of yours anyways ? Also how much can you add to it before the valves make contact with the pistons or the retainers hit the seal's?

Clymer manual says:

GS400B
intake: 36.265mm
exhaust: 35.735mm

GS400C
intake: 36.485mm
exhaust: 36.085mm

GS425
intake: 36.485mm
exhaust: 36.085mm


GS450
intake: 36.782mm
exhaust: 36.283mm

GS500
intake: 36.819mm
exhaust: 36.321mm

[pete]

This sounds fun! Best keep us up to date and then provide video

Stephen, those 450 spec's look a little off... sure it shouldn't be:

GS450
intake: 34.782mm
exhaust: 34.283mm

???

Once my ignition is sorted I will most likely be slotting some GS500 cam's in...

[Mekanix]

Your right Pete. (fixed) I was trying to do some math and forgot to edit that again.

I was thinking that it was 36.782 and then tried to figure out how much lift there was from 0 lift by subtracting the no lift diameter from that number.

For example:

With the GR650 cam's I have laying around,
They have a 37.2mm lift measured from the top of the lobe to the bottom.
I wanted to know the actual lift.
So the no lift zone measures. 28.02mm and the full lift is 37.2mm
That mean's the actual lift is 9.18mm or 0.367"

I was going to edit those numbers to show the actual lift but couldn't find the no-life number. so I was going with the diameter of the journal which is 22mm but that was wrong so I put all the numbers back to what it said in the manual and forgot that one.

First thing to note is how much lift your engine can take before you have to modify the pistons or valve guides.

[pete]

Cool, just thought it best to check

[Chuck78]

Are the GS450/500/GR650 cams a direct bolt in swap into the early 76-79 GS400/425?

I wonder how they'd compare to these mid level Megacycle Cams?

384-70
.380" 261° 107.5° 23 btc/58 abc .004"
.380" 261° 108.5° 59 bbc/22 atc .004"
Use modified pistons and springs. Best all around street and road performance. Increased
mid-range and top-end. Wide, smooth power band

.380" converts to 9.652mm lift. 9.18mm is the GR650 cams, which have much more lift than the other GS twin cams listed, so the mid level megacycle's are a pretty hot street cam, so it seems!

Their lower level cam is probably a good upgrade over anything from OEM twins even:

384-00
.354" 254° 110° 17 btc/57 abc .003"
.354" 254° 110° 57 bbc/17 atc .003"
OK with stock pistons and springs. Increased mid-range power in stock motors.

That is 8.99mm lift. 28.02 base circle plus 8.99 = 37.01mm lobe height, so taller than all but the GR650...

[Chuck78]

So that being said, I wonder if going big bore on say, a GS425 to 502cc with custom 73mm pistons and GS1100 shortened sleeves, if I could forego my thoughts of needing to have oversized valves installed and a good porting job done, and instead just substitute that for bigger cams? The bike is going to be snappier responding on the throttle down low without the porting, so maybe I should just look into going this route? It would probably be cheaper than a reworked head for sure, having two cam cores reground into this mid level lift profile. The extra cc's will give me more torque, but on the top end, I will probably not see the hp gains as a ported head would. Maybe a mild port job with stock valves and the mid level megacycle cams may be the best bet for my intentions.