I searched and read through a ton of threads but could not find the basic information I'm looking for.

I'm reading all the GM performance parts specifications for the LT4 HOT Cam, 1.6 roller rockers, LT4 retainers and LT4 valve springs.
Something doesn't seem to add up.
If you subtract the specified coil bind height (1.220") from the specified install height (1.780"), then subtract the maximum lift with 1.6 rockers (0.525"), the remaining clearance is only 0.035" (difference between height of spring compressed at maximum lift and height of spring at coil bind).
Everything I've read says that this clearance should be at least 0.050", if not at least 0.060".
I'm surprised that gm would sell a complete camshaft kit with a clearance of only 0.035".
Unless the recommended limit of 0.050" that I've read by every oem and aftermarket cam manufacturer for the last 20 years is not really necessary?

So my questions are:

Is the LT4 valve spring with LT4 retainer and 1.6 roller rocker install height actually 1.780" or is it higher?

Is the coil bind height actually 1.220" or is it lower?

There's got to be someone somewhere who actually measured all of these things. Thanks.

 

Your fiqures seems right with what I have read. The .035 to coil bind is why most recommend a better spring for the Hot Cam. I personally wouldn't run the LT4 spring with anything but a stock camshaft.

 

Lots of guys run around with less than .060" of clearance. it might not be ideal from a traditional safety standpoint but it works. I run a GM 846 cam with upgraded springs and roller rockers and I have only .045" of clearance...never any problems.

A reason for a better spring than the LT4 setup is for better valve control, not for more clearance. The installed height gives you the advertised seat and open pressures with the spring rate supplied. If you were to go to a higher installed height, with the same spring, you would have more clearance but lower spring pressures. That wouldn't be a good thing unless you like valves that float around...lol

 

According to this: http://www.lbfun.com/warehouse/tech_...ifications.pdf

it's 1.78

 

This is why I didn't install LT4 springs back in late '97. Way too close.

 

1.78 is also specified in the gm performance parts catalogs for the LT1 springs but I measured mine last night and they range from 1.752 - 1.765.

Catalog also lists solid height as 1.260 but my springs measure 1.198 when fully compressed.

And the stock stamped rocker arms have a 1.47 ratio, not exactly 1.5, which helps with clearance but also means the valve lift isn't exactly what is specified.

I'll get my LT4 springs and retainers hopefully today and I'll measure the installed height and post it here.

 

I'm a little confused by some of the comments here. How can a higher quality spring change the clearances? To do that you'd need a spring built from thinner wire or a higher installed height. What am I missing?

 

Yes the LT4 spring has a different shaped wire, like an oval which allows more compression before coil bind. The diameter of the wire may be different also. And the overall diameter of the spring is 1.32" instead of 1.30". The retainers are also different and should allow a higher installed height. I don't know if the thickness of the retainers is less or the geometry where the keepers fit is different but when I receive them I'll measure and find out. The LT4 shim underneath the spring may also be thinner than the LT1 shim (or whatever it's called).

 

I understand that the LT4 springs are ovoid. My question was directed at the guys who said they wouldn't use the LT4 springs because if the clearance issue. Unless the higher performance springs have a higher installed height or a thinner effective wire diameter, the use of a 'better' spring won't do anything to address the clearance issue.

Spring selection should be based on the cam and not be a 'higher rate is better' situation. All you're trying to accomplish is well controlled valve motions within the rev range you'll be operating. Every spring has a harmonic oscillation point but the higher the rate the higher you'll have to rev to. For example, if the cam manufacturer recommends a valve spring with a 130 lb/in closed pressure and a 340 lb/in open pressure with a cam good to 7000 rpm, putting in a spring that gives you 175 lbs/in closed and 500 lbs/in open doesn't accomplish anything except maybe give a person peace of mind that the valve won't ever float.

 

[SNIP=bw_hunter;6004559] For example, if the cam manufacturer recommends a valve spring with a 130 lb/in closed pressure and a 340 lb/in open pressure with a cam good to 7000 rpm, putting in a spring that gives you 175 lbs/in closed and 500 lbs/in open doesn't accomplish anything except maybe give a person peace of mind that the valve won't ever float. [/SNIP]

What about accelerated lifter and/or rocker arm wear due to the higher pressures? In your example, thats about a 35% increase in seat pressure and just over a 45% increase in open pressure.

Jake

West Point ROCKS!

 

I certainly agree with you but I probably wasn't clear about it. I don't understand guys that think that big, giant springs are the only way to build an engine....

 

I put it on to the AMERICAN WAY - Bigger is Better. Right!?

Jake

West Point ROCKS!

 

In my case, I didn't feel safe running those springs. Once they were checked, I sent them back to Dal and bought some different springs. Not giants but ones that could take the lift of a HOT cam.

 

Okay I now have new stock springs, retainers, new LT4 HOT cam springs, retainers, and tools to measure spring height and pressure.

Here are the results:

LT1 actual installed height = 1.760"
LT1 coil bind = 1.200"
Maximum lift with 0.050" clearance = 0.510"
Actual clearance with LT4 HOT cam, 1.47 rockers = 0.078"
Actual clearance with LT4 HOT cam, 1.6 rockers = 0.035"
Pressure at 1.780" = 80
Pressure at 1.760" = 90
Pressure at 1.280" = 270
Outside diameter = 1.300"

LT4 actual installed height = 1.760"
LT4 coil bind = 1.170"
Maximum lift with 0.050" clearance = 0.540"
Actual clearance with LT4 HOT cam, 1.47 rockers = 0.108"
Actual clearance with LT4 HOT cam, 1.6 rockers = 0.065"
Pressure at 1.780" = 100
Pressure at 1.760" = 105
Pressure at 1.280" = 270
Outside diameter = 1.345"

This information tells me that the stock LT1 springs should be fine for an LT4 HOT cam with the 1.5 (actually 1.47) ratio rocker arms.
But with 1.6 ratio rocker arms using the LT1 springs would result in 0.015" less clearance than recommended.

Pressure at 1.235" height is around 290 for both springs.
1.235" would be the maximum lift of LT4 HOT cam with 1.6 rockers with actual installed height of 1.760".
I don't know how accurate my spring pressure testing tool is but it shows that the pressure of the LT4 spring is greater than the LT1 at installed height, but about the same at max lift.
Pressure values are about the same as GM spec at 1.78" height.
But the GM spec for average rate (lbs @ in) are 373 for LT1 and 332 for LT4 - don't know exactly what that means.