I found a site showing both the LT1 and LT4 valve springs. When I compared the numbers, I saw very little difference. the most notable was the LT4's higher seat pressure of 101#, but at the same installed height as the LT1s (1.78").

What else is there that makes the LT4 springs so often recommended when going with 1.6RRs or the HotCam, etc?

Here the numbers that were posted on the site:

LT4 - Part number 12551483, 1.32" OD, 332# per inch average pressure, 1.22 solid; 101#@ 1.78" seat pressure

LT1 -Part number 10206040, 1.30" OD, 337# per inch average pressure, 1.26" solid, 85#@ 1.78" seat pressure.

If these posted numbers aren't correct, please straighten me out. If they are, what's the big deal?

Thanks, Jake

West Point ROCKS!

 

The LT4 spring is made from ovate wire allowing a higher lift before coil bind.

 

Hot Cam and 1.6 rockers gives .525 lift. LT1 springs are solid at .520. Not a good combination. LT4 springs don't have that issue.

 

Okay, I just put on my "thinking cap" and crunched the numbers. So, if the numbers on that site are correct, here's what I came up with:

The installed height for both springs is the same 1.78".

Now, the LT4 spring coil binds at 1.22" = So if you subtract 1.22" from 1.78" you have .560 at coil bind.

If you subtract the needed clearance between the coils as a safety factor, while most recommend .060, the LT4 springs, running with 1.6RRs on a Hotcam would give a valve lift of .525", the LT4 springs would only offer .035 clearance between the coils.

Yep, the LT1's won't cut it because they'd coil bind at .520" even before the HotCam with 1.6s has reached the max lift of .525

The average difference between the two springs, per inch of travel, is only 5#, with the LT1s having more 337 Vs 332.

So, I mean why would I opt for a set of springs that are struggling to handle only .525" valve lift?

What am I missing here? There's got to be something magical going on here.

What about these guys who are running well over 150# on the seat with cams only one step longer in duration than the HotCam? You set the HotCam to have 101# on the seat, yet when someone moves to, say, a 224/230@.050, the seat sky-rockets to over 150#.

I'm just wondering how such a big difference in seat pressure and, yes, spring rate per inch, can be recommended for cams that are not too different.

Anyone have the advertised duration of the HotCam and at what lifter rise it was measured so I can try to calculate the aggressiveness of the ramps as compared to other cam offerings?

This spring thing has got me going because I'll be turning some wrenches before too long and want all my ducks in a row.

Thanks,

Jake

West Point ROCKS!

 

You make a good point.

Hot Cam 218/228 525/525.

My cam 224/230 605/622, and I'm running 155# seat and ~400# open pressures.

 

Because they are a $35 drop it fit, upgrade for people not intending to go bigger than a Hot cam.

http://www.jegs.com/i/GM+Performance...95494/10002/-1
The recommended springs for my HR Lunati 243 /251 560/565 cam are only 108lb seat / 339lb open but a 460 lb spring rate.

 

Thanks for that feed-back.

I'm wondering if it's the ramp design of the cams that makes the difference. As you probably know, the aggressiveness (or lack of aggressiveness) of a particular cam's ramps isn't shown on the cam card. We get lots of "numbers", but nothing about the ramps to allow us to compare one cam with another.

So I came up with a layman's way to making a comparison. What I do is compare the advertised duration at .006" with the duration at .050.

The lower the difference, the more aggressive the ramps. That's why I need the advertised specs on the HotCam, so I can calculate the ramps.

From reading some of the information in the CompCams catalog I've found that the more aggressive the ramps are, the more spring is needed, especially for lifter control over the nose.

The higher pressure springs prevent the lifter from being launched off the nose of the cam as reaches max lift.

What added to the confusion in this whole mess is that TPIS' claim 125# to be the max seat pressure for a hydraulic roller cam.

I intend to follow the cam maker's recommendation for which springs to run with the cam I choose. I'm making the assumption (Yea, I know) that they've done their homework and know which spring works best with a specific cam. But I still want to know why there are such conflicts in spring recommendations.

My search continues.

Jake

West Point ROCKS!

 

Good luck with your research; let us know what cam you choose.

Joe B.

 

That's a good start for a 'ramp rate' comparison, but you have to account for the overall duration as well. The proper way would be to calculate "inches per degree", as in inches of camshaft lift per degree of camshaft rotation. The lobe duration is measured relative to a standard lift amount (I don't remember exactly what), but you can subtract that standardized lift from the max lift of the cam to find the overall lift increase. Then divide that by 1/2 the duration of that lobe. This would give you the "slope" of the lobe, though that term isn't really applicable since it's round.

GO NAVY

 

My son wants me to install heads and a cam on his 96 LT1. So I'm doing my homework.

I plan to go with 1.7's, but in going that route, I have to factor in the acceleration rate of the cam's ramps.

I've read some semi-negative posts about the HotCam, some saying it's an "old" design and that better offerings are now available.

Since I'm a Die-Hard CompCams guy, I want to be able to compare Comp's offerings with the HotCam: Duration, lift, LSA and ramps.

Many of the more aggressive cams that Comp offers have a rating of right at 50 (+/-) The XFI series comes to mind, but there are other lobes even more aggressive.

For a street engine, which his is, I'm a believer in aggressive ramps. But if I opt for one of Comp's more/most aggressive cams, then put 1.7s on it, I may end up being over the top because I know that the higher RR ratio also causes greater acceleration of the lifter by itself. Couple the fast ramps of the cam with the increased acceleration rate caused by the 1.7s may be too much.

So, basically, I want something in order to make a comparison. Since the HotCam is designed for 1.6s, knowing it's numbers could help me see what's what.

I like fooling around with this stuff too. LOL

Jake

West Point ROCKS!

 

NAVY!!!!!!! LOL

Right, I should have included the duration and valve lift considerations in my previous post.

What I plan to do is what I've done in the past. I'm going to compare apples to apples and eliminate as many variables as I can.

I plan to compare cams with the same .050 duration and make sure that the advertised durations are measured at the same point, usually .006

So, as I see it, if I know the advertised duration at .006 and the duration at .050, I can see how quickly the lifter travels from .006 to .050. That'll give me a handle on the aggressiveness of the ramps.

Here's an example: Take a cam with a AD of 288 @ .006 and a .050 duration of 224. Subtract 224 from 288 you have 64. Now take a cam with the same .050duration (224) but with an AD of 280 @ .006 you'd get 56.

So the 280/224 would have more aggressive ramps. Without knowing the .006 advertised duration I'd have no way of knowing how quickly the lifter would reach .050; I'd be missing one of the numbers I'd need.

Another thing I look at is valve lift when two cams have the same duration numbers.

For example, say you have two cams that have the same .006 and .050 duration figures but one has, .590lift while the other has, say .661 lift, that tells me the .661 cam is more aggressive.

I'm now beginning to see why cams with lazy ramps don't need as much spring as those with aggressive ramps. That makes me start thinking that the HotCam has lazy ones. That would explain the rather low 101# seat pressure the HC springs call for.

Think I'll do a Google search to see if I can find the full specs on the HC, then I'll know for sure.

For me, this stuff is fun the play with.

Jake

West Point ROCKS!

 

Just curious Jake, why the 1.7 rockers? Do you already have those rockers? If not, why not buy a camshaft with the specs you are after using 1.6 rockers?

 

Duration
@0.006 cam lift 279° 287°
@0.050 cam lift 218° 228°

 

Jake, sounds like you're building a screamer, right on.

So it seems that shorter duration and higher lift = faster slope, (aggressiveness).

Part of this will be addressed if you go with Comp Cams 1.7 rockers. As I understand they are designed to create a quicker lift and longer duration on their own. At least that's what they advertise.

The wrench in this combination is going to be piston to valve clearance. This will be determined by all of the factors especially the heads you choose or have chosen. I would look at this carefully as a bad result would be catastrophic.

As I understand the LT4 springs are good to a total .575 lift before coil bind. Your combo will require at least a spring with .600 lift. As far as seat pressures I'm not that educated yet, but this post may help that along. I would imagine however that just about any spring rated at .600 lift is going to be designed for this type of application. A call to Comp Cams might be in order here. Then let us know. I have thought about going with a bigger rocker as well with my Hot Cam.

 

Wow those springs are cheap, perfect for my ghetto rebuild on a homeless budget lt1. I must stop dreaming of beehive springs. I will not be revving like a s2000.

 

It's because I'm want to hit around .600 valve lift and CompCams says it's best to achieve your lift goals with rocker arms, rather than with the cam.

So, since those guys are at the top of their game, when they talk, I listen. LOL

Jake

West Point ROCKS!

 

Thanks!

That puts the HotCam at 61, which means it has pretty conservative ramps. The CompCams offerings with aggressive ramps come in at the low 50s.

Crane has an offering they call Inverted Flank Rollers and Comp has one called CRC (Constant Rate of Curvature) which are of the same design. Both of those series really widen the area under the curve.

Much appreciated.

Jake

Wast Point ROCKS!

 

I like their products also. My cam is a Comp Cams custom grind, and Pro Magnum rockers.

 

Right, when doing a build like this and push the envelope this way, I always use the clay method to be sure I have at least .100" intake and .125 exhaust.

When I clay, and if I don't have at least that clearance, I'll just exchange the 1.7 rockers for 1.6s.

Jake

West Point ROCKS!

 

I found some specs for the LT4 valve springs on a website. The installed height is 1.78" and coil bind is 1.22"

So if you do the math, you can see that the max compression at coil bind is .560. 1.78" minus 1.22". Now remember, that would be WITHOUT any clearance between the coils, which most recommend should be .060".

I'm assuming the specs I found are accurate and, if they are, the HotCam springs can't handle .575". Of course if the spring specs I found are wrong, then all bets are off. LOL

I've talked with a local, highly regarded small block dirt track engine builder who told me that sometimes racers run springs with as little as .040" without a problem.

Well, if you then subtract .040 from the .560, you only have .520. Now we know the HotCam has .525 valve lift with 1.6s, so that tells me they're running with ONLY .035" coil clearance.

Going with 1.7s on HotCam springs would put max valve lift at .555" which is so close, you might as well call it "coil bind". .005"

Now I'm wondering if anyone has actually measured the coil clearance at max lift of HotCam springs.

Also, the Advertised Vs .050" duration specs of the HotCam helps explain how it is that cam can get away with so relatively little spring seat/rate pressure.

I really appreciate the info, guys. It's helping me fill in the gaps.

Jake

West Point ROCKS!