993 hydraulic rockers adapted to early engines ?

Mukilteo911 · 10-28-2003, 09:35 AM

Since I have never had a 993 rocker to look at and compare, I ask if anyone thinks it would be possible to adapt a 993 rocker or specificly the hydraulic valve lash to the earlyer 911 engines.

If it is not the right size shape is if feasable to have it resized, shaped etc ?

This would be for a non race engine in an attempt to procure better mor consistant economy.

350HP930 · 11-01-2003, 03:33 PM

I think the extreme difficulty in getting pressurized oil to the rocker shaft would be the big road block to such a project assuming that the rockers are even interchangable.

Cam profiles are also specific to whether the engine has mechanical or hydraulic lash adjustors.

Wayne 962 · Wayne 962's Garage

And the advantage of this would be? (besides not having to adjust the valves)

-Wayne

911pcars · 11-01-2003, 09:14 PM

"And the advantage of this would be? (besides not having to adjust the valves)"

If you were successful to get that far, you could go to the next step and try to implement some sort of variable valve lift scheme.

, but other than that, I don't see any big upsides.

Sherwood
http://members.rennlist.org/911pcars

aigel · aigel's Garage

In the V8 world, folks go back to solid lifters to make more power. A hydraulic setup will rob some umph. Adjustment may not be everyone's favorite, but it will be far less expensive even if you outsource it, than trying to go to hydraulics.

Cheers, George

HawgRyder · HawgRyder's Garage

I had also thought of this idea.
The problem seems to be the amount of room inside the cam covers.
I had looked at the Harley Davidson early hydraulic unit as a possible design...they are about 3/8" diameter and 1 1/2" long....designed to be inline with the pushrod and supplied by low pressure oil from inside the pushrod.
They appear to be more of a damper than a true hydraulic lifter...but perhaps that's all we need.
If the eccess gap is taken up when the pressure is off the valve, then the overall gap could be larger and the valve noise would dissappear.
Maybe....
Bob

Bill Verburg · Bill Verburg's Garage

The main advantage is weight, the 993 hyd rocker setup is 15g lighter on the intake and 21g lighter on the exhaust than the mechanical type. Only the racing shim type is lighter. The hyd. work great and do not use extra hp. They do need different cam ramps.

Besides room the oil supply would need to be worked out, 993 have lifter oil supplied from the cams via a peripheral groove on the front of the cam bearing and on the cam itself.

HawgRyder · HawgRyder's Garage

Bill...do you mean the lifter picks up oil on the leading edge as it rotates?
Bob

Bill Verburg · Bill Verburg's Garage

No, the hyd. lifter oil gallery in the heads is fed from a groove in the cams and cam bearings
964 cam

993 cams

The cam drive is also different but that is another issue

Wayne 962 · Wayne 962's Garage

Quote:

Originally posted by aigel
A hydraulic setup will rob some umph.

I have heard this in many, many places, yet I think it might somewhat folklore. Does anyone have any specific info on this?

The problem with hydraulic lifters on a VW or 914 engine is that the lifters tend to float at higher RPM, reducing power. Is that the same on these Chevy engines? I would assume that this doesn't happen on the 993? I know that the BMW engines have a small check valve built into the lifter - I think this might help to reduce lifter float?

Anyone have any more info on the subject?

-Wayne

911pcars · 11-02-2003, 04:45 PM

Here's my theory or something I regurgitated from something I might have read.

Pushrod engines have the added weight of a pushrod in the valve train; something not usually found on overhead cam (OHC) engines that work directly (or through intermediate rocker arms) against the valves. At high RPM, the added valvetrain weight causes the parts to separate a little. This add'l clearance is then quickly taken up by the hydraulic lifter which is inherently designed to reduce valve train slack. Without adequate clearance, the valve can't seat thus power is lost. In addition, a hydraulic lifter (with an internal piston, spring, check valve, circlip and oil) is also heavier than a "solid" lifter which is essentially a hollowed out steel or cast iron cylinder.

Another thought is that the oil pressure in the system can't bleed out of the lifter faster than oil pressure builds up with increased engine speed, thus it tends to gradually reduce valvetrain clearance.

Sherwood
http://members.rennlist.org/911pcars

Bill Verburg · Bill Verburg's Garage

The hyd. lifters are a proven design currently used on the GT3(red line 8200)
here is a cross section of a lifter

and of the head

Doug Zielke · 11-02-2003, 05:23 PM

Quote:

Originally posted by Wayne at Pelican Parts
The problem with hydraulic lifters on a VW or 914 engine is that the lifters tend to float at higher RPM, reducing power.

This is also true on Harley-Davidson m/c (OHV, pushrod) engines.
Builders of performance H-D motors, use solid lifters or so-called 'Hydro-Solids' (they act like a solid lifter only at higher engine speeds).

350HP930 · 11-02-2003, 05:55 PM

The biggest problem with hydraulic lash adjusters is that they compress and leak and therefore do not provide consistent lash control.

HawgRyder · HawgRyder's Garage

The diagrams are of great help.
As I see it now...the hydraulic part of the lifter is fed from the oil passage coming through the rocker shaft leading to the tip of the rocker and then through the top port of the hyd unit (the top diagram being shown upside-down).
So...if the rockers of non-hydraulic type and the hydraulic type are approximately the same size and ratio...all one would need is the oil feed passage drilled into the cam cover to provide pressure.
The rocker shafts could be modified or replaced with different ones...and the cam would stay the same (for the profile)..and all extra play would be taken up by the hydraulic units....the lifters themselves becoming solid when in actual crush between the cam and valve stem.
After all...we only want to get rid of the lash...not re-engineer the cam profile.
Bob

aigel · aigel's Garage

Sherwood is right on the money why hydraulic lifters (in pushrod V8 applications) are making less power. I always think of it in coupling: With a solid lifter you get the maximum lift transferred from the cam to the rocker, there is no 'soft' component, nothing to pump up etc. The rocker to valve clearance is all you need to take up with the solid lifter.

I personally think that hydraulic lifters are a great thing. Even if they rob power (which doesn't seem to be the case in the flat six), I'd rather try to find power elsewhere. Maintenance that involves getting into any part of engine isn't for me. This goes for timing belts too. Once they are affordable, I will get a 993 with those hydraulic lifters and OBDII...

George

911pcars · 11-02-2003, 11:05 PM

Obviously, Porsche went to some expense to incorporate automatic lash adjusters (hyd. lifters) into the valve train. Whether this was to enhance power (doubt it) or to reduce maintenance (probably), I'm not positive. Perhaps their oil drain schedule didn't coincide with a manual valve adjust schedule, or they figured they could eliminate this service procedure altogether using an automatic device to improve engine longevity without limiting engine speed.

However, with all these small oil passages and add'l parts, clean oil and regular maintenance is even more important.

Sherwood

Mukilteo911 · 11-03-2003, 09:01 AM

The hydraulic lifters looked like a fantasic little part that would provide less maintance and possibly better fuel economy due to the valves being more consistantly adjusted.

The question I still have is does anyone know if they are the same size, profile as the regular lifters. And also can the lubricating issue be addressed ? I had totaly missed that issue before. Oil for the lifter looks like the killer deal.

911pcars · 11-03-2003, 10:40 AM

Prior engines did not use hydraulic or mechanical lifters. There were no lifters. The rocker arm is the only device transferring motion between the camshaft and the valve.

Installing a hydraulic mechanism to automatically adjust the valves is NOT a DIY project. One might want to spend R&D brain cells and money on something a little more constructive. Did anyone see this in Wayne's project book? I took this question as an interesting theoretical question, not something anyone would seriously look at just for the convenience of eliminating scheduled valve adjustments. But if someone wants to, be my guest.

Sherwood

Mukilteo911 · 11-03-2003, 10:59 AM

Did not see it in Waynes book. Since I had not seen the newer rockers I had no way of knowing the diffrences in spec. Sometimes one comes across parts that will work well with minor mods. I had pondered the idea if it were feasable with limited mods. But it does not look like a good idea given the information. I am suprised someone has not made 3rd party rockers to emulate the newer stlye ones, seems like a good idea., I guess I will just pull out the ole dial and readjust.