Valve lash settings

[Ken S.]

Tooking for valve lash on the dontov 30/30 cam that is in my 64 fj.
We have totaly rebuilt this car to ncrs spec. Now its time to fire it up!!!Can anyone help me Thanks in advance Ken

[William C.]

Re: Valve lash settings

Lash spec is .030 intake and exhaust. If you search the archives, there is a lot of information on how to position the crank to make the job more accurate. Just search "lash settings" and more will be there than you imagined.

[Joe C.]

Re: Valve lash settings

If your car is a '64, then the original cam for your engine was a "30-30", not a "Duntov". See attached:

[Dan H.]

Re: Valve lash settings

Just reset my 64 FI with 30-30 cam at the balancer 90 degree setting method that Duke and John recommend, I set each at .023 as per instructions, car runs GREAT! Idle is at 900 rpms, dwell at 30, the idle vacuum did drop from 15 to 13 but still has a solid idle, sounds as a Vette should! Also, I have an original 326 VAC that is fully in at 8 psi, be careful of 'repo' units that come in later, lots of problems there if not careful. Good Luck!!!
Dan

[Ken S.]

Re: Valve lash settings

Thanks for the info

[Joe C.]

Re: Valve lash settings

Just reset my 64 FI with 30-30 cam at the balancer 90 degree setting method that Duke and John recommend, I set each at .023 as per instructions, car runs GREAT! Idle is at 900 rpms, dwell at 30, the idle vacuum did drop from 15 to 13 but still has a solid idle, sounds as a Vette should! Also, I have an original 326 VAC that is fully in at 8 psi, be careful of 'repo' units that come in later, lots of problems there if not careful. Good Luck!!!
Dan

Dan,

Idle vac sounds a little high. Understand it should be closer to 10-11" @900 with a 3849346 ("30-30"). Your idle vac sounds more like a "Duntov" (3736097) cam from 57-63.
My lash is set according to Duke/John's method, but a little wider, @ .025". Engine pulls about 10" @ 900. Set @ .023", my engine's vac drops by a RCH, to just under 10".
Do you know the specs/manufacturer of your cam?

Joe

[Ken S.]

Re: Valve lash settings

Don is your car a TI? what is 326vac?

[Dan H.]

Re: Valve lash settings

Joe, my cam is a LT1 30 -30 and pulls more vacuum, I didn't want to set the valves any tighter and lose driveability of low range. Believe LT1 specs were .016 and .023 but I went `.023 accross the board and it still is very easy to drive.
Dan

[Duke W.]

Re: Valve lash settings

You should reset your inlets to .016". The point of the tight lash specs is to insure that the valves are lifted off and placed back on the seats at clearance ramp velocity as explained in the paper.

The idle condition should be about 900@12".

A massaged head, blueprinted, LT-1 cammed '65 327/365 made 80 percent peak torque at 2100 and 90 percent at 2500 set at .016/.023. FI might not be quite as good because of the single plane manifold architecture and may need a little higher idle speed.

Either way, a LT-1 cam will make better low end torque with about the same top end power as the 30-30, which is why I recommend the LT-1 cam to replace all 30-30 applications - as did Chevrolet!

Duke

[Michael H.]

Re: Valve lash settings

Either way, a LT-1 cam will make better low end torque with about the same top end power as the 30-30, which is why I recommend the LT-1 cam to replace all 30-30 applications - as did Chevrolet!

Duke

Chevrolet didn't exactly recommend it. You do but GM replaced it in service for completely different reasons. That was the beginning of tighter emission standards and the old 346 cam was "a little dirty".

If someone is restoring a Corvette, I recommend the correct original factory installed cam.

[Duke W.]

Re: Valve lash settings

I think the fact that the LT-1 cam replaced the 30-30 in service is sufficient endorsement.

Both cams had relatively low NOx because the high overlap left a large exhaust gas residual, but both produced high HC. The LT-1 cam makes much better road friendly low end torque than the notoriously torque shy 30-30.

Also, I challenge anyone to consistently be able to distinguish the two based on operating characteristics. It's not possible to do this including a PV.

Duke

[Michael H.]

Re: Valve lash settings

Also, I challenge anyone to consistently be able to distinguish the two based on operating characteristics. It's not possible to do this including a PV.

Duke

That's not a good arguement. If, as you say, they're near the same, why bother to install the wrong cam to begin with?
Who street races old 60's Corvettes today, anyway? And if they do, do you think a slight change in the torque curve is really going to make a difference?

Some kid is going to come along in a new C6 that daddy bought and kick azz anyway. Why beat a dead horse and make unnecessary changes to a C2 or C3 that do nothing? Just seems pointless to me.

Besides, the LT1 cam doesn't sound as good as the old 57-63 or the 30-30 for 64-65.

[Duke W.]

Re: Valve lash settings

It has nothing to do with racing. The LT-1 cam has greater low end torque and better low speed operating characteristics than the 30-30 cam, which makes it a better choice for a NON-race car. The 30-30 IS essentially a racing cam.

And again, I defy anyone to CONSISTENTLY tell the difference by idle sound alone.

If you want to argue about "correct" restoration, how many guys today are painting vintage Corvettes with lacquer as opposed to a modern system that they then try to "massage" into looking like lacquer.

There's certainly more to discuss on this issue than arguing about two camshafts that are nearly identical and indistinguishable other than to a vacuum gage. Recall that the LT-1 cam uses the 30-30 lobe on the exhaust side advanced 4 degrees. The primary difference is its use of the L-72 lobe on the inlet side which is effectively about 8 degrees shorter.

How about pre-'67 non-SHP engines. Most are restored with the "incorrect" '67-up 929 base camshaft (which are indistigishable from each other to all but a detailed crank angle-lift check with a dial indicator) or the 929s replacement - the 839.

Shame on them!

Shame! Shame! Shame!

Duke

[Michael H.]

Re: Valve lash settings

It has nothing to do with racing. The LT-1 cam has greater low end torque and better low speed operating characteristics than the 30-30 cam, which makes it a better choice for a NON-race car. The 30-30 IS essentially a racing cam.

Well, as usual, I disagree, but I knew if I started in on ya again on Lt1 cams, I'd get some response. You been kinda scarce around here and I couldn't resist.

Duke, what's the status on you're 63? Is that car still all apart?

[Joe C.]

Re: Valve lash settings

Joe, my cam is a LT1 30 -30 and pulls more vacuum, I didn't want to set the valves any tighter and lose driveability of low range. Believe LT1 specs were .016 and .023 but I went `.023 accross the board and it still is very easy to drive.
Dan

Dan,
Whaaaaahh? What is a "LT1 30-30" cam?

Ken,
There is no such animal as a "dontov 30-30" cam.

It looks like everybody wants a "piece" of the beloved "30-30" cam, whether they really have one or not!

There were 3 distinct SBC/SHP camshafts, chronologically:

3736097: aka "Duntov" ; 1957-1962 283/327 SHP produces about 13-14 in-hg @ 800 RPM. Worked well with Rochester Fuel Unit because it produced sufficient vacuum at idle.

3849346: aka "30-30" ; 1964-1965 327 SHP, 1967-1969 302 "DZ" Camaro (Z28). Did not work well with Rochester Fuel unit as original specified lash settings of .025/.025 did not produce sufficient idle vacuum for the Rochester Fuel unit to settle down to a stable idle. This camshaft acquired its beloved moniker ("30-30") after Chevrolet engineers specified a wider than optimal lash in order to "detune" the cam by removing some lift and duration. This thereby enabled all L76/L84 SHP engines to achieve higher idle vacuum, allowing the L84's Rochester Fuel unit to produce a stable idle. Another effect of the wide lash was to produce better driveability (i.e., low/midrange torque). A third effect, was to increase mechanical tappet noise, which is considered "cool" in some circles. This was the most radical, or high-strung camshaft ever factory-installed in a SBC.
Regarding the L76 application, its induction system was an old design, more suited to the older "097" camshaft. The 30-30 cam was severely hamstrung by a highly restrictive intake manifold, and undersized carburetor.
The 30-30 cam was much better served by its DZ Camaro application, which used the much more efficient 3917610 intake manifold, topped off with a 750 CFM Holley dual feed carburetor.

3972178: aka, none ; 1970-72 350SHP (LT1). Because this cam was installed in a larger displacement engine, and equipped with the high flowing 3972110 (DZ clone) intake manifold, and similar Holley 750 as used on the Z28 engine, it was probably conservatively rated at 370 gross HP. It probably delivered closer to 380.
If the "30-30" cam, together with the 1964-65 2 1/2" outlet style exhaust manifolds were fitted to this engine, its gross output would have been closer to 400 HP!

Joe