Penguinracer

Thank you all who responded to my previous query regarding rods & pistons for a modded motor.
My earlier post regarding the most durable after-market rods & pistons raised the issue of the importance rod & piston weight, especially as operating RPM increases.
This begs another question - what is the realistic rpm limit for the hydraulic lifter set-up & at what point do solid lifters become advisable?

TonyG

With a high quality TI spring and retainer package, stock valves (or at least stock valve weights...) and stock lifters you can get about 7200-7300rpms before valve float. The lift on the cam is limited with a hydraulic lifter because you can only cut the base circle of the cam down so much before the the lash is too big for the hydraulic lifter... thus cam dimensions with hydralic lifters don't really factor in much.

That said... it's a high enough rpm that the stock rods don't cut it...

It's also high enough in the rpm range to dictate that if you don't have a very expensive top end setup that can breath big numbers, with a correspoinding cam, intake, exhaust, etc... there's zero reason to go to a solid lifter. In other words... if your peak HP isn't at 7000+rpms, you don't need solid lifters, but if it's getting close... I would put in a set of after market rods for sure.

TonyG

TurboTommy

Another question would be:
assuming the engine can breath, how high of valve spring pressure can you go with the hydraulic lifters to ward off valve float, and then how fast can we spin the engine without going to solid lifters.

But then there's also the issue at what RPM does oil pump cavitation become an issue.

333pg333

How high do you want to rev? I was under the impression that you wanted to build more of a flatter torque type of motor.

Chris White

The stock valve train max RPM is several hundred RPM high than you want to run the stock oil system….

333pg333

In the words of the immortal McLeod "There you go Chief"

Penguinracer

I have a dry sump system (LR) ready to go but I'm interested in retaining my original block so I have a matching numbers car. Realistically that gives me the option of a 2.8 stroker or retaining the 2.5. My gut is to stick with 2.5 so as to reduce piston speeds & bottom-end stress plus I understand that the 2.8 has smaller detonation margins than the 2.5
I'm leaning towards a big valve N/A head, 70mm throttlebody, stand alone management, appropriate Garett turbo & FMIC, bigger oil cooler & bigger radiator. If a higher rpm solid lifter set-up with the appropriate cam will improve the VE of the 2.5 that is something to consider in comparison to the stroker option. The car is not & never will be a daily driver & it'll be running on R rubber with usual chassis mods, RE camber plates,Guard 50/80, Leda coilovers (450F/350R), 27mm T-bars,Tarett a/r bars, Elephant Racing solids throughout, KEP Stage I PP/disc with a Spec billet steel f/wheel, Big Blacks with the 33/5 valve & RS29s etc.
I welcome advice as to my plans.

m42racer

Cam choice or design dictates the Lifter type, nothing else. I was told the hydraulic tappets are good for 9000 RPM, but as it has been stated, nothing else in the engine unless changed is good at that speed.

Remember too, solid tappets can hurt the performance if the clearances are not set correctly or maintained. They require a special cam design and this design is all about the lash and when the cam starts to act upon the tappets.

Ronin-951

900 rpm. My experience is they are great for LOW rpm benefits, before Oil pressure builds. High lift, steep ramp cams are reasons to go solid in a street car, or, a feeler gauge addiction.

TonyG

>>>High lift, steep ramp cams are reasons to go solid in a street car, or, a feeler gauge addiction. <<<

That's incorrect. The stock and aftermarket solid lifters are both flat tappet designs, which means both share the exact same ramp angle limitations.

It's not until you go to a roller tappet that you can take advantage of steeper ramp angles. And that's not the case here.


>>>900 rpm. My experience is they are great for LOW rpm benefits, before Oil pressure builds.<<<

I'd like to see before and after tests to see any real measurable results. I've heard arguments like this before (mostly on the internet) but have yet to see somone show any real gains.

And even if it were the case, it would be probably be trivial at best.

Show me the money....



TonyG

User 52121

With all the mods done does it really matter that you have a #s matching car?

I thought the only real added value of having a car with matching #s was for originality. With heavy mods you're kinda no longer really "original"...

Dougs951

Are 944 blocks serialized?

JDS968

Which brings up the question, why has nobody gone with roller lifters/cams for the 951/968? Once you're already going to the trouble of converting from hydraulic to solid lifters, is the additional difficulty of adding a bracket to align the roller lifters prohibitive?

savvas944

solid lifters are great for high lift /long duration cams,which both 951/968 dont have at least on the duration side.
Less mass to reciprocate i.e better spooling and and better wear and tear ,with ability to fine tune
cam gap.No hydraulic collapse and indepentent over the oil pump.
To retrofit the 951 is an expensive alternative ,for what the benefits are offerring.

Seems that the benefit is more on the 968 ,S2 16 valve engine with bigger throttle and injectors
and when used with
better rods ,and high lift/much longer duration and overlap cams,which after calculating the cost/per hp
makes you wish that you should change to a Turbo rs replica.

TonyG

The reason is because of the cam tower design.

Roller lifters cannot be allowed to rotate on their axis (in their bores) where as flat tappets can (and do).

There's no way to keep this from happening because of the cam tower design.

That's the reason.


TonyG