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Roller cam and lifters with flat tappet valve springs

5K views 25 replies 10 participants last post by  ericnova72 
#1 ·
So my question is can you use them together. My valve springs I have right now are "Z28 valve springs" what I have seen is people saying flat tappet springs are to hard on the roller lifters but I'm trying to match a cam that requires the same lift or can handle those springs? Thank you
 
#3 ·
Two big issues are rollers are heavier than flats and cam designs between

1. Roller lifters weigh about twice a flat tappet lifter. Roughly about 200 grams installed compared to 80-90. part of this is the roller and part is the alignment mechanism.

2. Here though with the cam you have to be careful of the lift rate. There are two dimensions of duration that play into this that is the duration between zero and .050 lift. The older Z28 flat tappet cams use a lot of duration in ramps between zero and .050 where more modern cams and especially rollers whack the ramp duration about in half or more resulting in a lot more jerk load on the valve gear including the springs. Insufficiect spring pressure with these roller cams let’s the closing valve bounce on its seat.

Bogie
 
#4 ·
Okay so looking into stock vortec cams just because of price and I can get stock rollers and from what bogie has already said in another thread I can drill out my bosses for the stock spider tray so my plan right now is getting a stock cam stock springs stock lifters used but still good dog bones with a gm cam and gm lifters for a somewhat stock setup but my setup is somewhat stock I think. I have dart heads ss iron eagle 76cc chamber with an eagle rotating assembly bored .30 over flat top 4 valve relief pistons. The reason behind me thinking of doing a stock cam is because budget but what do you think bogie?
 
#5 ·
There is quite bit of overlap for valvespring applications.
Mid and upper end of range flat tappet spec is the same as base and mild level hydraulic roller.
Same on the range for upper level hydraulic roller swap to mild solid roller.

What hydraulic roller do you have in mind??
Probably more importantly, do you have the valvespring part number??
 
#9 · (Edited)
#10 · (Edited)
When you get down to what the OP is doing; that is using the stock timing L31 Vortec cam is pretty mild it is roughly equivalent to the pre 1987 standard production 305, 327, 350 cam.

In this cam’s heyday, depending on compression ratio, this produced between 250 and 300 horsepower from a 350. In the L31 96-2000 these are rated about 250 hp which is consistent with the cam timing in the not high performance 350 before SMOG requirements reduced compression ratios into the high 7’s to low 8’s.

So I think his Z28 springs using a production timed L31 roller will be just fine.

Bogie
 
#12 ·
So I think his Z28 springs using a production timed L31 roller will be just fine.
I agree. I have a set of stock L31 springs in my shop somewhere, and I'd bet they don't have as much seat pressure as the PO's so-called Z28 springs. Those GM roller cams were not all that aggressive. Even the 196/206 RamJet cam has a seat duration around 278/288.
 
#15 · (Edited)
A half inch lift is worthy of investigation, that is quite a bit more than the stock Vortec cam.

The spring you cite, the Melling VS-380 is just a stock replacement spring of pretty low pressures of 84 psi to 204 open at .045 inch lift. .45 inch is their recommended max lift point occurring with the spring compressed to 1.25 inches high from a closed install height of 1.7 inches. At a fully open point there needs to be a sum of coil to coil clearances adding to .050 inch. If you add .050 inch to .450 inch range of function of the installed spring this is .5 inch and your cam lifts to .500 inch lift so on paper the springs you have are at coil bind, they can’t be operated that way.

I don’t have that spring around so can’t check real measured numbers for you but on the face of it unless you can come up with measures, I’d say you need different springs or a different cam.

Bogie
 
#23 ·
With the heads on there are two common ways of tackling this job.

Bring each cylinder as you work on them in turn to near TDC. Remove the spark plug and stuff a length of rope into the cylinder leaving a generous length out side for retrieval. Then bring the cylinder being worked on to as close to TDC as the rope allows. This supports the valves being worked on from underneath Their heads. Then with the tool made for this purpose to compress the spring to remove the locks, retainer and spring.


The other process is similar but uses compressed air to hold the valves shut. This requires an air compressor and suitable hoses and fittings to connect into the working cylinder’s spark plug hole, which can be difficult around the exhaust and other obstructions. The piston moved to TDC and the crankshaft jammed in that position to prevent the air pressure from pushing the piston down the bore. This latter step is to prevent the piston from giving enough distance to allow a valve to drop all the way into the cylinder should a failure occur.

Bogie
 
#20 ·
All technical mumbo-jumbo aside, if you float the valves with roller lifters, you will pound out the needles in the rollers and that's it for the engine. (that's why there are bushing roller lifters - they wear out before needle bearing rollers, but don't grenade if you float them).
 
#24 ·
I prefer rope over air. I've never had an issue with the rope leaking out of the cylinder and letting the valve fall in.
 
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