425r

[clutch22]

Any opinions on a 425cc big bore kit for the R ?
I've never heard of a bore kit that big for the R.
Here's the website where i found it.....
http://store.4x4tuff.com/3.html

[oldskoolex400]

if your gonna spend that much theres a complete sabertooth 510r motor in the forsale section for $600 more, that is what i would do and get to keep your engine

[RichM1983]

Not sure what you want such a big motor for but from what Ive read the PSI 425 is hard on wrist pins and tears them up fairly quickly. I cant say for sure but thats what I have read. Also that may not even be a PSI kit but it does look like it.

[C-LEIGH RACING]

Rath ran the PSI engines for awhile in the GNC nationals & as I remember didnt finish to many events.
I have held those cylinders in my hands & they were a piece of art, how they were made & those head designs were way before their time with the on the fly adjustable dome. Just loosen a set screw & change the dome & compression in about 3 seconds.
I realy think the down fall of those top ends was that Big Air carb they had with the adjustable high speed fuel jet.

PSI company was a big snowmobile engine builder & every engine they built was top notch.
Neil

[clutch22]

Originally posted by C-LEIGH RACING
Rath ran the PSI engines for awhile in the GNC nationals & as I remember didnt finish to many events.
I have held those cylinders in my hands & they were a piece of art, how they were made & those head designs were way before their time with the on the fly adjustable dome. Just loosen a set screw & change the dome & compression in about 3 seconds.
I realy think the down fall of those top ends was that Big Air carb they had with the adjustable high speed fuel jet.

PSI company was a big snowmobile engine builder & every engine they built was top notch.
Neil

Soo... what happend, Rath blew his engines in alot of races?... soo i probly shouldnt get it?
When i comes to Big Bore Kits, do you think ESR is better than PSI?

[C-LEIGH RACING]

I think PSI had some good stuff, but was just one of those things that had some bugs to work out.

Its kinda like if you were to take a 2 stroke engine builder that for the most part of their career only did drag engines & then switch them to porting woods type engines, it would take them awhile to sort things out to make the engines work right, just a train of thought thing.
PSI was heavy into the snowmobile type engines with a belt drive system & the whole build up, design & way of thinking is different on one of those over a engine with a transmission that has to shift gears & vari rpms all the time.

As far as getting one, if its at a good price, may be ok to try, but dont get it just cause one person said it was ok.

I would like to have one myself just to work on & see what it realy was causing all the problems with them, & like I said before, I think one of the problems was that big air carb most everybody was clamping onto them.
That carb was another story right by itself & just like the head a item before its time.
Neil

[genoapb]

I cant say everybodies experiance would be the same but my ill share my experiance with one we use for drag racing. First off, we had terrible luck with the adjustable dome. It practically took a breaker bar to turn it and it always leaked from the combustion area into the coolant. We also had rod breaking issues once we starting spinning higher rpms. I cant really comment on the psi carb as we ran a 44mm lectron on alky. The pipe was also crap in my mind. We tried a number of combinations to try and get the motor to run with the stock porting with no luck. Our drag 250-370 would consistantly beat this motor. With the stock porting, the best we could get it to run on a 300ft track was 4.8's. In all fairness, you cant really expect a motocross type port to perform that well when trying to drag race but for comparison weve used these same methods in the past on a stock ported 250 and ran 5.1's. So this past season I completely rethought the entire combination revolving around a stronger lt500 rod as well as a 76mm stroke. I also ported the motor to better suit drag racing. I then decided to remachine the original psi head to accept domes in the same way a pro design head or something similar does. We also switched to a pipe designed for a 500cc engine which worked alot better but still could use one designed for our motor. Any way, the point is I think there is potential there it just really needs a pipe designed for your type of riding and the added displacement as well as a well thought out combination. The rod issue should really be looked into as well or you will break it. Rebalancing the crank is also a very good idea. With the new combination I ran this past season it ran considerably better and there was more there but I just ran out of season for testing different dome designs, timing, carb size, pipes etc. It ran into the 4.3's on this combo. We will keep trying new ideas with this motor since we already have it and its paid for but if we had it to do over again I would go with a prox motor or for all out performance and reliability id go with a sabertooth 500 kit. The biggest problem with the psi motor is like someone mentioned already, no one has really spent alot of time trying to develop it like the prox which has been around for ever as well as the huge price tag. The sabertooth hasnt been around as long as the psi motor but Saberracing has done all of the devolopment for it already and it makes awesome power and has been really reliable to boot. Man, ive been rambling on for some time now! I dont want to sound like im bashing psi but for the money a prox kit or saber would be the much better choice in all aspects. IMO

[C-LEIGH RACING]

There you go clutch, straight from a owner of one.

You know, its hard to beleave a top end set up that looked that good would be that bad, but you start adding up all the little problems & it turns into one great big one & then you add the price. It wouldnt take two or three units with the owners having that many problems & word would spread fast.
Thanks Alex,
Neil

[genoapb]

C-Leigh, your exactly right all of those little things add up in a hurry. I also remembered a coulpe other details that may have helped the motor out when rethinking it. I cut a small window in the piston to provide better lubrication to wrist pin bearing as well as cool the underside of the piston. Also when I added the 143mm long rod a super thick .500" spacer was needed under the cylinder which also increased the transfer intake area and may have well been another weak link in the cylinders design without it. The longer rod also aiding in increasing the area by raising the piston and essentially making the side cutout on the bottom of the piston bigger. Of course this area could have also been increased with either a different piston or by cutting the windows out bigger on the psi piston, which just for the record I dont believe was actually designed for the psi cylinder it was just something suitable they already had available. Thats jmo of course.