Porting the head and other power upgrades

[Stabler]

Been a while since I was last on here.. Been way to busy with my other scoot. BUT now it's time to give my XS400 some long needed love!


Since my head gasket is leaking I have to change that one. So I thought, while I've already got the head off I might as well try and get some power upgrades done. I know this isn't a speed monster and can't be without NOS or supercharging it, and that's not what I'm after here.
I wan't it to be reliable and get a bit better low to mid end performance. I (almost) never try to red line it anyways, so I figured the power band most used is the one I should adress.

I've searched like a tool on this site to find some clear instructions on how to port the head, without using a flow bench or dyno (of which I've got neither). I know better than to just put the dremel to it and eyeball it, so I'd like some advice on this part. Anyone got any tips or pointers on porting the head?


I also wonder if there's enough material on the head (or cylinder) to have it ground down some to get a little more comp? Anyone ever done that? With any success?


And if I get some useful and good pointers on the port job (and maybe even the comp job) I might consider getting a new cam as well. This part is kinda pricey, $210 + shipping to Sweden, but if the other "low budget" things pan out, it might be worth it? If it doesn't interfear with any comp job to the head/cyl that is.


And last, maybe another set of carbs (just because I've just got these puppies all dialed in )? I've read about the GS440 carbs being bolt on, but will they ad any noticeable power gain? Or is there any other carbs that can be made to work? (Not spending a fortune on new CR carbs that is).


I have already got pods and hiflow silencers on it and I've dropped almost 50 lbs off it when I chopped it (yes, I weighed the chopped of parts and the new ones I put on it), so the natural next step would be porting, cam, carbs and maybe more comp.
I'm also thinking of getting new piston rings and stiffer valve springs while I already have it apart. Can't hurt right?

I'd really appreciate some good tips, pointers and ideas here.

Thanks in advance.

 

[16VGTIDave]

If you want bottom end torque, I'd suggest you rethink some of your mods.

Porting will cost you torque and polishing is even worse. Make the ports smaller and rough!
Cams usually cost torque. Stay with stock cam ('s?) and increase your valve lash to the max specified to reduce valve lift and overlap.
Higher compression should get you torque.
Smaller carbs or a single carb will gain throttle response but limit RPM's. Larger carbs will reduce response and might increase high RPM performance.
Smaller exhaust pipes will increase torque at low RPM's but limit high rpm.
An exhaust cross-over pipe before the mufflers will usually increase torque, especially in the mid-range.

New rings along with a honing of the bores can't hurt, as long as you seat the rings properly during your break-in period. Stronger valve springs are only required for high rpm operation.

HTH,
Dave

 

[drewpy]

use an adjustable powerband

http://kalecoauto.com/index.php?main_page=product_info&cPath=11&products_id=36

 

[Stabler]

Yeah drewpy. Along with some blinker fluid.

http://kalecoauto.com/index.php?mai...oducts_id=22&zenid=vabv4oup9eggcbtggo72k0hfs5

So, Dave, you're certainly right and physics is physics. The only thing I see is to get more comp and maybe glass blast the intake side of the head.

This leaves me with two other questions. Bigger bore? I can't find any kits, anyone know how much one can punch the cylinder bores? And how much can I actually machine off of the head and/or cylinder (to get more comp) without the risk of my valves hitting my pistons?
Anyone knows?

Thanks.

 

[drewpy]

you can get to 450cc with wiseco pistons

 

[Greasey Fingers]

how much would the weisco kit cost you reckon?

 

[Scorpio1963]

how much would the weisco kit cost you reckon?

Sometimes you got try google,Its my best freind.

 

[xschris]

I have never seen one for sale Weisco don't even stock xs400 pistons anymore.

 

[drewpy]

you have to contact them, and they will make some.

 

[xschris]

There was a guy on here a while ago that did that and in order to do a production run you need to buy like 4 or 5 sets I don't think he did it because it was over $1k and I don't think that included rings, that was for standard size pistons. Maybe it has changed now but I could not justify that kind of money for a few more cc's

 

[Stabler]

Oh - great. Really. Massive $ isn't what I'm looking to spend right now anyways.

So, drewpy or xschris or whomever that might know, is there any material to get machined of the head or cylinder to gain comp? Or isn't it enough to get any noticeable gains?

Thanks again guys.

 

[xschris]

The sohc xs400 (U.S.models) came 9.2:1-9.4:1 compression ratio's the 82 sohc had 9.3:1 so you could remove some of the head to get it up to 9.4:1 The xs360 had a 9.6:1 head so I don't think it you would have any problems get it up to that. With that said how much material to remove I don't know that is up to the machine shop guy. Also you will have to look at the stroke of the engine and how the valves line up. Running a higher compression engine will require hi test fuel and will make more heat and pressure on the crank. You could give the head a 3 angle valve job to make a better valve seal (stock is two) but the seats wont last as long. I would just clean up the ports from high casting ridges smooth out the exhaust ports and be happy with it because in the end if you spend thousands of dollars to blueprint the engine with all the mods that can be done your still looking at a 45-50hp bike stock is around 38hp

 

[Greasey Fingers]

Sometimes you got try google,Its my best freind.

Well I wouldnt want to get in the way of your friendship now would I?

 

[Stabler]

Thanks xschris. That's kinda the answer I needed.

 

[Greasey Fingers]

The xs360 had a 9.6:1 head

Hi Chris, does that mean the xs360 motor was more torquey?

 

[xschris]

I guess it would have had a more snappy engine that the 400. With only 33cc difference between them putting a set of 400 pistons in the jugs should not be to hard. The carbs they used had a lot more fuel flow before the emission standards took over and they used a more leaner carb for the 400.

 

[Stabler]

So 360 carbs on the 400 is the way to go?

 

[xschris]

I would say yes because of the non-emissions set up and the way they are built and the idle mix screw are on the sides of the carb. Much easier to adjust I have not had a chance to run them yet with winter and all plus bike is inside now for the winter.

 

[Stabler]

Good to know. Specially since neither cam nor port job seems to be the way to go for me..

 

[Greasey Fingers]

hmm interesting, thanks for the info Chris! I actually just picked up a 360 motor & carbs recently off ebay for $230. Motor turns over and sounds like its got compression too. Hey do you know what the diametre of the carb diapragm is on the 360 carbs, would it be the 70mm or 73mm version?