Rebuilding 350cc for performance. Need advice.

[ruredy]

Originally Posted by scottyb

A friend did this and yes you need a '91 igniter. You do not need any milling to increase compression, you will need to run high octane fuel....Compression is extreeme. you will want a little cam and some jets and a fuel pump. Good Luck

All you need is to put on the 295 head, High octane gas may be a good idea but since it's a flat top/dish piston design, flame propagation is normally very good with that design allowing you to run lower octane fuels. It just kinda depends if detonation is a problem (engine knock), As far as jets and fuel pump the engine basically isn't going to use more fuel than it would without the 295 head, If your going to extremes and porting out the head, new ss valves, stiffer springs, open exhaust, cam, and of course an ignition setup that will allow it to spin faster, then you may need fuel pump and new jetting. But in my opinion, these engines aren't design to spin very fast and it would be better to do a gear change then to try and spin them faster. I also would not do anything until after you have it running. then check the plugs to see how it's running (rich or lean) and adjust from there unless you feel like throwing a bunch of money at it. I have heard that these engines tend to blow up around 5700 rpm so even if you do get a igniter with no rev limiter you'll need a tach and a light foot to keep from grenading it.

[cpu77]

I will bore my 350cc .50 over and put the 295cc head on it. I am going to add a cam. Maybe advance the timing a bit. I bought a jet kit already (Have not installed it). Where do you get stiffer springs? That may help with the valve float. Anyhow I will give you guys a heads up as I go. If you can think of anything please let me know. Thanks so much for all your help!



On a side note what is a good running 295cc going to bring complete with clutch?

[cpu77]

OK guys it appears I could run a GM HEI ignition and aftermarket coil. This would remove my rev limiter. Here is the thread I am refering to.

GM HEI Ignition Install

[ruredy]

Originally Posted by cpu77

OK guys it appears I could run a GM HEI ignition and aftermarket coil. This would remove my rev limiter. Here is the thread I am refering to.

GM HEI Ignition Install

That is for a 2 stroke, the inductive pickup (pulsar coil) on the 4 strokes works backwards from the 2 strokes. It has a constance magnetic field that is triggered when the field is broken, the 2 strokes and HEI's are triggered when the field is created. This gives the HEI module fits and it starts firing erratically. This may work if you were to embed a magnet in the fan and use a inductive pickup for a 2 stroke placed to where the magnet would pass over it. Placement of this setup would be critical and it would also need to be adjustable for timing advance.

[sstuck2]

Originally Posted by ruredy

You know it's not hard to get power from this engine, the problem is that the igniter has a built in rev limiter. So no matter how much horse power you get out of this engine it will still limit the rpm's and in turn limit its speed. No matter if you have 11hp or 111hp. your cart is still only going to run in the mid 20 mph range (depending on tires) without changing the rear end gear.
Because it is limited in the rpms you don't really need huge carbs, open exhaust, big cams, all these things may add power to the engine but how are you going to use all that extra power. The best mod for a 350 is to install a 295 head on it. This bumps up the compression quite a bit which means more horse power. This will put the 350 right up there with the smaller vtwins use in these swaps you see so much about. The problem then is the rev limiter.

So can you fix the rpm problem by a taller tire? As in maybe put the 1" shorter belt for the low end, put in a cam for added torque to help keep the heavier/taller tires turning in the mid to top end, etc... for lack of better words - just make it really strong through the rpm range available?

[WickedCarts]

our robins hp motors are 295 with .50 over and a milled head makes 15hp and with a 25" tall tire 30 mph

a stock 295 with fast fredds super charger also ran 30mph with a 23" tall tire

we are wanting to put the super charger on a 15hp and maybe add cams and msd see if we cant get 45 mph

personally i would mill the 350 head... they have made 2 different heads

one like the old 295 with a cast iron exhaust manifold and the new style no manifold... the 350 head flows more air it just needs compression

[WILD-BILL]

If this helps here's the run down on my cart.

350cc W/ a 295 head. Hardened valves and seats with high rev springs. Oil cooler and Mobile 1 syn oil. 1" shorter belt. MSD ign. stock rear end W/ factory gears. stock tires at factory ride height.

Best MPH so far has been 30 mph according to the GPS.

I have been thinking about high speed gears, cam, jet kit, head work and a free flow exhuast.

Also, I've been running high octane pump gas and have had no detonation issues.

[Marvin73]

Which MSD ign did you use?

[BuggyHunter]

What happened to further development on this one this thread. It was interesting.

Have any of you got further more detail to add.

Disregarding the IGN REV LMT issue, what about the speed Gov connected from drive shaft gearbox to the accelerator. Would that not limit speed.,

In any case could this increased HP assist in increasing torque for hills.
Ie maintaing close to 30MPH uphill. And carry higher payload.

I don't have the skills and tools to do this mod.
Can anyone recommend a reliable workshop that can assist.,

What about Hydroxy booster. Anyone played with this to increase power?

[Bondohead]

bump
i am also looking into this type of mild hop up.
BH- 350 w 295 head isnt 15-17 hp. it is 13
mabe mabe not hi test gas. i hope not needed. if it is mabe octane booster cause i use ethnal free in all my small engines and it is not avl in any hier than 87
CT Rebuilders in Agusta ga sals this motor.