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LT4 Hotcam in L31
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"Retainer to guide clearance is the primary Achille's Heel of the Vortec.
For valve lifts above .460" they need to be checked for R-G clearance"

-Gary Penn, formerly of GM Performance Parts

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L31Sleeper wrote:
"Retainer to guide clearance is the primary Achille's Heel of the Vortec.
For valve lifts above .460" they need to be checked for R-G clearance"

-Gary Penn, formerly of GM Performance Parts


yes - in stock form. the beehive springs and different retainers and locks allow for .550 MAX!! i test fitted a cam with .547 lift and did not bind.

ive seen those heads machined for up to .700 lift, which i think is a waste, but seen it. if your gonna machine the head, id go for a .650 clearance.

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Ok, got some pics to show you guys!


The majority of articles I read said: Stock Vortec heads= .480 max lift.

All my intake valves clearance were at .510, but the exhausts varied...

Check out my R-G clearance of cylinder #6 exhaust:




Study the seals on this picture:


Looks like they creep up.

Using a washer and a socket I tap the seal down.




Seated.




I gained .068 clearance!?



Now with the Comp 787:



Almost .570 of clearance!

+ .600 if you use + .050 lock!!!

No machining involved!!!


As for spring bind...

Zeroing the retainer thickness:



I can estimate the sping install height at 1.750. with comp 787 retainers and stock locks.




The comp 26918 springs bind at 1.100"

So, 1.750 - 1.100 = .650" of spring clearance.



-Ben-

(The other one)

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Ben, I can't really comment on the technical stuff, but I see some awesome pictures with great lighting/photography in an otherwise challenging situation.

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Give up mechanic work and be a photographer Razz

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Thanks!! Very Happy ...... I think.... Neutral Laughing

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Thanks man, good pics. What does the end of the valve stem look like with the +0.050" locks installed? Is there enough of the valvestem protruding to catch a self-aligning rocker? I have heard that sometimes there isnt enough poking through.

The question is moot, if you are using guideplates.

EDIT: for brutal spelling
peace
Hog



Last edited by Hog on Mon Jun 08, 2009 4:52 pm; edited 2 times in total
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Those are the comp 648 locks. (Standard height)

The stem extends 0.147



I've got magnum 1.52 rollers. The side washers stick out 0.065 more than the roller.



So that leaves 0.082 clearance.


I think + 0.050 locks would work.

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That's good stuff. Even I think I understand and I haven't built an engine in decades.

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Guys! you won't believe this!

Look at the valve tip (red circle)



When I took the picture, I had installed my old locks.

Notice how the locks stick out from the comp787 retainer .

But not on this one:


So I redid the R/G measurement with the comp 648 locks....

How does .600 sound?


From .450 to .600 no machining involved just reseating the seals + comp 787 retainers + comp 648 lock!

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you one crazy caliper weilding foo'...

great info and pics to boot.

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so I can run lt4 hot cam on my stock 1999 l31 heads with springs and 1.52 rr with out mchine work?
what about zz4 cam ? wat springs and rockers are good for it ? do I have to change the pushrods to ?

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As L31Sleeper said:

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a stock vortec head is only good to .460

The Hot Cam is :

.492 with a 1.5
.525 with a 1.6



.499 with 1.52

You'll need to make sure that all your seals are well seated and you'll have to use:

Comp cam Beehive springs 26915 or 26918

Comp cams 787 retainers

Comp cams 648 keepers.


With that combination, I've mesured .600 seal to retainer clearance.
-.060 for safety, you should be good up to .540 max lift.


But even then I would not run it without measuring seal to retainer clearance as an "out of spec" head could have passed through production.

You can buy a cheap digital caliper @ Summit for $33.00


http://www.summitracing.com/parts/SUM-900017/?image=large

I've paid half of that for mine at a local store.

Not as good as the $200.00+ I use at work, but good enough for home stuff and cheap insurance.


CarCraft mentions 774 retainers but those are Gen III.

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CrazyHoe wrote:

You can buy a cheap digital caliper @ Summit for $33.00


http://www.summitracing.com/parts/SUM-900017/?image=large

I've paid half of that for mine at a local store.

Not as good as the $200.00+ I use at work, but good enough for home stuff and cheap insurance.


You can get ones just like that at your local Advance (if there is one) for ~$25. I have them, and they work fine for just about anything that I need. I even did a rear-end with them (measuring shims, etc).

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I'm looking at getting the hotcam and I have done the 918 springs with 787 retainers, but I think I used the stock locks/keepers

so right now I should be good for .550ish lift???

when I put the cam in I'm going to pull the heads to change the locks/keepers to the 648

that should get me in the safe clearance range for the hot cam and 1.6rr at .525???

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You loose .050 with the stock locks.

You still need to verify the seat to retainer clearance for all valves because of variance in manufacturing process.

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I was just flicking through my manual yesterday and it showed that gap between the seal and seat as being the way they're supposed to be installed???



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Ooooops!

No free lunch, is there

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That still puts clearance at .560 though.

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Sorry for the late reply, but I had the LT4 Hotcam with black box and bolt ons on my stock 350 short block and it bogged down low real bad. Had to get a 3000 Vig converter to make it drivable. I had the same Vortec ported heads that I do now, with a tune from Fastchip... and it did put down 310 rwhp (so true to the 400 hp article) but it was all up top. Search all my posts and you will get an idea of what it ran like. With a heavy truck, any loss in torque is magnified in drivability.

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