Heavy Duty Valve Springs = More RPM's??

austinpankratz

If I put heavy duty valve springs in my HF 420 clone, will that bump up my RPM's that I can squeeze out of the motor?? (Of course not wide open throttle for very long, just in bursts)

BGW

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raydhd

You will need better pushrods and higher lift rocker arms give you more top end kick.My VC 460 easily pulls 5000 even with 24" tires.

Streetbu

I used 35lb springs from VC in my 390 and it pulls to 5k all day long, runs out of breath with the stock cam that high but helped a lot compared to the stock valve springs. It's a must do if revving past 3500 rpm...

Field6565

The heavy duty valve springs alone will get you what you are looking for. Yes the 1.3.1 rockers and aftermarket pushrods are nice but not a necessity. I would also remove the governor internally. You wouldn't want that to come apart at higher RPMs.

sho305

I have a lifan 420 its supposed to have better pushrods you don't need to replace. I put HD springs and 1.3 rockers in and it went from 4300 max to around 5200. Its hard to tell the $15 tach gets strange over 5K. I did use the valve locks and button on both valves, and the valve spring seats under both. I rarely wind it up that high but once in a while I test it or hit a short section of road where I can. It has ported and cut head and timing key, header, it seems to be strongest right at 4K rpm so I clutched it there. Still has stock carb, jetted of course. I removed the governor before I put it in the cart.

I would tell you to run 10 gal of fuel through it before you put the springs in, so its broken in good before you rev it hard over 4K! They can seize a rod if you scream them without enough run time. Also if you run it constant at 5K or more you should put a rod in it, you must if you put a cam in it. Last thing is make sure you clean and blue loctite the block cover bolts again when you button it up, or they will come loose on you later.

Just goes to show the stock cam is not much good over 4K, even with those mods, but going down the road it will pull up to 5K no problem now then it slowly goes a little more if I keep it pinned. Suppose the stock carb could be slowing it there but does not feel like it because it will keep near top speed at half throttle. However it should run nicer with a better carb, you can't get these jetted perfect they just don't have enough circuits.

slonomo

The problem with the stock push rods and the stock rocker arms is they are prone to failure at higher than governed rpm. The stock pushrods will likely bend. The stock rocker arms will likely break. Don't take the chance. If you are revving your engine, build the valvetrain right.

raydhd

I can't imagine taking the governor out adding HD springs and not at least getting rid of those skinny stock push rods.Again I just can't imagine doing that and not waking the engine up with the 1.3 rocker arms.

sho305

Lol, dunno it still runs fine. Don't know if the rods are different or not. Waiting to see if I want to put a cam in then I'd go with SS valves and all that. But I might work on a new cart instead.

raydhd

As you have also found the 1.3 rocker arms give some extra boost for 1000 rpms or so.

sho305

They give a top end boost but they don't seem to move the powerband really, though only a cam typically does lol. At 4200 shift it was certainly slower.