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Old 03-30-2012, 03:59 PM
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Hydrolic flat tappet cams

I need to be schooled a bit on hydrolic flat tappet cams. I have read quite a bit on them and from what I have found they are horrible at higher rpm (anything past 6500rpm) and above.

If one were so inclinded to have a custom cam ground (estimated) to say;
112lsa 110icl
@50 247intake 260exhaust
.550intake .660 exhaust

This would kick the rpm to at least 2800-7000rpm (from my understanding, correct me if I am wrong) on a 350ci block with correct intake and heads bla, bla, bla.

There was some limited talk about gm using some sort of combination to make it so that the hydrolic cams could safely run to about 7500rpm. If it was lifters or something else it really wasn't clear to me.

Do any of you fellas have any information on what makes a hyndro cam live (meaning reliably and still making power) at such a lofty rpm?

I think this would be great info for those who have been using solid flat tappets and would like to use a hydro in a smaller mouse motor say as small as a 283 etc.

Thanks in advance for the info.

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Old 03-30-2012, 04:14 PM
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The only way to get a hyd cam to rev as high as a solid cam is to adjust the valve lash so there is no lifter preload or a very slight .001" to .002" valve lash.

This very tight lash window requires very frequent valve lash resetting to maintain. Lots of hot engine oil mess, burned fingers etc.

You will have the valve covers off hundreds more often then if you just ran a good solid lifter cam. A good solid lifter cam set up pnly needs valve lash adjustment once or twice a season.

Setting the valve lash on a solid lifter SBC is very easy and pain free.

Excessive spring pressure on any flat tappet cam attempting to hold off hyd lifter pump up will wear out the cam.
There is no free lunch.

You are wasting your time trying to reinvent the wheel.
If you want to rev it beyond about 6700rpm get a solid lifter cam.

Why are you bothering with this.? adjusting a SBC solid lifter valvetrain is not a big hassle at all.
All you will achieve is a lot more $$$$ hassle and a short cam life and limited real performance by trying to force a hyd cam to do what a solid cam does a whole lot better.
all for nothing. Especially in a good old lil 283

if you got a real 10:1 or 10.5:1 try a cool Isky Z/27 cam #201027
Put some gears in the car 4speed manual or 8" 9" race converter.

set the valve lash cold at .016" Set it and forget it for 6 months to 1 year.
7000+ rpm and lots of power with the right isky dual springs or the isky 235D single springs. 130# installed seat pressure.

just saved you big bucks and a lot of needless hassle.

Last edited by F-BIRD'88; 03-30-2012 at 04:23 PM.
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Old 03-30-2012, 05:19 PM
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From my understanding there is sort of race part that makes it that one does not have to adjust the lash as you had claimed. I have read where people had said the same as you. I am curious if there is any other way around it. I have been reading a lot today, playing around a lot with DD. I came across a post in reference to hydo cams etc and thought to ask the question seeing the statement was never challenged per se.
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Old 03-30-2012, 05:26 PM
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There are lots of newer V-8 engines that can rev to 7000rpm and some can go higher than that, with hydraulic valvetrains. The Corvette LS-7 comes to mind. They do this with a very light valvetrain. They run sodium filled valves, or titanium valves, lightweight beehive springs, chromoly or titanium retainers, light/stiff pushrods, and perfect geometry.

I have a 350 LT1 engine sitting here that has seen 7k repeatedly. The lifters are adjusted just like F-BIRD'88 advises. Basically you tighten the rocker until there is zero lash, and then you just BARELY snug it down a little more. Mine are about 1/16th-1/8th past zero lash. By doing this you don't give the lifter the ability to pump up and hang a valve open. I also ran Comp 918 beehive springs, chromoly retainers, machined locks, and chromoly pushrods. Valves were stock 2.02's in my TFS heads. Nothing exotic at all really. Just a good combo.
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Old 03-30-2012, 07:27 PM
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thanks for the reply that makes a lot of sense. I will discuss what you said further with travis knowlton at thunder head in bethel.
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Old 03-31-2012, 06:15 AM
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my compcam 292H cam pulls hard right up to valve float in my 350 which is 7200 rpms.

Needs the proper springs for this. I am using a little more spring than what compcam recommends because that is what came with the 200cc dart heads.

I have seen a few dynos with the 292H cam and it seems to make max power at 6900 rpms in a 350.

The 305H cam is even bigger.

However, my best ET's where made shifting at 6500 with that cam. Even through the engine feels like it is making good power above that.
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Old 03-31-2012, 06:53 AM
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I have also read somewhere that the hydro cams kill tq compared to a roller or a solid non hydro. I tried that in my DD program and the program agrees.

Have you noticed the same?
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Old 03-31-2012, 06:53 AM
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Quote:
Originally Posted by joelster
There are lots of newer V-8 engines that can rev to 7000rpm and some can go higher than that, with hydraulic valvetrains. The Corvette LS-7 comes to mind. They do this with a very light valvetrain. They run sodium filled valves, or titanium valves, lightweight beehive springs, chromoly or titanium retainers, light/stiff pushrods, and perfect geometry.

I have a 350 LT1 engine sitting here that has seen 7k repeatedly. The lifters are adjusted just like F-BIRD'88 advises. Basically you tighten the rocker until there is zero lash, and then you just BARELY snug it down a little more. Mine are about 1/16th-1/8th past zero lash. By doing this you don't give the lifter the ability to pump up and hang a valve open. I also ran Comp 918 beehive springs, chromoly retainers, machined locks, and chromoly pushrods. Valves were stock 2.02's in my TFS heads. Nothing exotic at all really. Just a good combo.
The LS7 also has titanium connecting rods! Making a 350 spin to 7000rpm is a lot cheaper then making a 427 do it.
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Old 03-31-2012, 02:53 PM
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Why are we spinning this motor that tight? I m an old school guy, I ran both hydraulics and solids. Basically a Hydraulic profile cam is street and strip. Max RPM6000, like on a street motor. Race motor, solids that can see 7000, with the right valve train. Most Hydraulics quit makeing power @ 6000 just by profile design. Besides to rev higher, you would need a stiffer valve spring that would collapse the lifters at lower RPM and oil pressure. Many solid cams still make power through 6500 rpm and beyond, so again, whats your intendid use?
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Old 03-31-2012, 03:16 PM
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There are lifters made to be zero lashed. Any lifter that doesn't have the good internal C-clip type retainers I wouldn't advise zero lashing. Look into Schubeck lifters, there are probably others as well.

The Schubeck lifter is shown at the top of the page HERE. Click on the caption for a link to them.
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Old 03-31-2012, 04:21 PM
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A hydraulic lifter will bleed down at some RPM, especially when the oil is flaming hot.
I would just run the solid lifters on the hydraulic camshaft, lash to zero-.002", and call it a day. I have run many circle track motors like that.
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Old 03-31-2012, 06:25 PM
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My experience with the 292H compcam is I doubt the lifters bleed down that much at idle as the cam is very lopey at idle and has very poor idle vacuum (8 inhg at 1000 rpm). So, I would say the valves are still openning quite a bit at idle.

Plus a power band form 3000 to 7000 rpms.
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Old 03-31-2012, 07:53 PM
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Quote:
Originally Posted by 454C10
My experience with the 292H compcam is I doubt the lifters bleed down that much at idle as the cam is very lopey at idle and has very poor idle vacuum (8 inhg at 1000 rpm). So, I would say the valves are still openning quite a bit at idle.

Plus a power band form 3000 to 7000 rpms.
The lopeyness comes from the long duration and the overlap.
That cams power band is 2500-6500.....set up right
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Old 04-02-2012, 05:25 PM
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Sort of off topic but does relate, at what point does the gm HEI start having issue? As in what rpm?

One would think they would have a similar rpm limit for factory parts.
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