Gx390 valve springs

Rkruf

New member
Who makes the best valve springs for running cams in .440 to .480 range at the valve? My valves are 3.650"
 

manyfunnies

New member
Ask your head builder. If you haven't had major head work then I ask why are you running so much lift when its giving you no added power.
 

JPR57

Member
We are running .550 to .600 lift at the valve on some of our 390,460 based engines. I believe the 390 that finished 3rd in the 2016 Nationals has around that much lift. With the right head work, custom ground cam and carb combo it adds a broader power band, however it is not a plug and play kind of addition. Lots of custom valve and head work is involved. Such as taking automotive titanium valves and machining them down for this application, welding up the rocker base to raise it up to accommodate the longer valves/taller lift, as well as modifying the piston to handle the valve lift.
 

Rkruf

New member
Spring pocket are not cut yet. I'm getting everything I need before doing anything. I'm doing my own work. What's the part # for those springs Jody? Thanks in advance
 
You want mild?
Or do you want the best?

I'm surprised to see anyone say .500+ in a kart engine. That was unheard of or considered a "drag race" only type of thing to kart racers. Anyway, I been doing the titanium .550"+ lift valve and spring setup for over 8 years now. So it's good to see others finally catching on
 

Rkruf

New member
Whats your advise mini drag bike? Love the vids you put out. You are one of the guys who got me thinking big
 
The big blocks are really limited on head flow. So it's your job to get the most flow you can. All these engines are just air pumps.

You want the "lite" titanium valves because the valves will be very large. You also was a very large welded port, or weld on tube to the head to get as much as you can. Then run no less than .500+ in the engine
 

Rkruf

New member
Thank you mdb I was thinking welded port extention to straighten out the angle I have a guy welding up the chamber now. I told him I'll be back for more. By the way blue devil number 4 sounds sweet....just get that starter socket off before you hurt somebody..lol
 

Oman

Member
As a starting point my mild 40mm intake valve head with no welding is about 150cfm @ 28". That's definitely a mild engine (high 30's hp) so work your way up from there. Multiply your HP goal by 4 and you will be in the very (very) rough ballpark for what head flow you need.
 
Sorry, but I don't come on here much. And 150cfm is pretty good for the 40mm intake valve. But the more you can get the better, nothing less than 150cfm.
 

Oman

Member
My HP goal numbers are on pump gas with compression down around 12:1 or lower and timing to suit. Run big compression and methanol with suitable timing and your probably talking 45hp from the same 150cfm, but I need reliability more than outright power. I'll be using a 355 lift cam and and 1.3 rockers, that's wild enough to get the job done, lift/diameter ratio of 0.3 is pretty tame.
 
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