Realistic Redline For The Stock Hydro Valvetrain

[JCviggen]

A guy I know with an 800hp 5-banger was getting valve float at 7500rpm on the stock springs, but that was solved with stronger ones. He did run a lot more lift on the valves than stock, somewhere between 10 and 11mm I believe that makes all the difference for what rpm you can get out of the stockers.

[boostdoctor]

No I don't think anything is collapsing, if it was, i doubt I'd make peak power at 7500. If anything though, keep in mind that at high rpms lifters don't typically collapse, they tend to do the opposite. As you approach valve float the lifters tend to overextend and hold the valves open.

I having a hard time following your theory. In my expierience, valve float usually come from weak valve springs. In this situation the springs aren't exerting enough pressure to allow the lifter to follow the cam's lobe prolfile. Most of my experience is with pushrod motors and in these motors the lifters do tend to collapse at high rpm in the 7000rpm range. Usually when you reach the limit of a hydraulic lifter; the power will flatten out up top and not really cause valve float. The design of a lifter in a pushrod will not allow it to over-extend. There's a plunger in the lifterbody and it's held in place by a retainer clip. The plunger can't extend beyond this clip unless it breaks....and i never seen one break. I havn't studied a Volvo lifter to see if over-extension is possible; so I'm not saying that you are wrong. I just basing my theories on my experienc with other type motors with hydraulic design.

[volvo500bhp]

A guy I know with an 800hp 5-banger was getting valve float at 7500rpm on the stock springs, but that was solved with stronger ones. He did run a lot more lift on the valves than stock, somewhere between 10 and 11mm I believe that makes all the difference for what rpm you can get out of the stockers.

Sounds like a fun car what ftlbs does it have ?

[InitialDriveGTR]

Would re-seating the valves and changing the angle make much difference? I would agree that using stonger springs on the valves would help with the float issue; but I'm not exactly sure you would be able to hear valve float on hydraulic lifters.

(please don't bite my head off, I just started to build my first engine)

[Captain Bondo]

What float issue? There is no float issue.

[Captain Bondo]

Boost Doctor my post is not a "theory". Hydraulic lifters pump up when the valves float, there is no longer any spring pressure on the lifter. You actually lose compression on a few cylinders when this happens and often the motor won't start after, until the lifters bleed back down. They don't come apart they just try to "adjust".

This is extremely common with the 16v heads as used on redblocks, stiffer valvesprings cures it.

You can potentially make lifters collapse but that's a different issue. With direct-acting valve trains at least(none of these motor have pushrods of course), the end of the valve stem is no longer being pressed against the tappet by the valvespring, so the tappet tries to expand to meet it and therefore ends up being too extended and it hold the valve open.

Regardless this is confusing the issue, since the hydraulic lifters are fine for 99.9% of people here. The only time I would see an issue is with hot cam like Russ and JC have said. I am running early 960 cams to 7600rpm with no issues. They don't collapse above 7000rpm.

[InitialDriveGTR]

What float issue? There is no float issue.

Didn't mean you had a float issue, was just saying in general. Like I said, I'm trying to learn this stuff.

Now how long do the lifters usually take to bleed out? Over multiple drive cycles?

[ozzimark]

I think he means more that the problem with valve float isn't there. It doesn't happen unless you have high lift cams, or are spinning the engine way too fast

I plan on running an 8k redline on my built engine with solid lifters and the stock turbo cams, provided that power isn't dropping off drastically by then. If it does, I guess it's time for a new intake manifold and cams :ph34r:

[InitialDriveGTR]

I think he means more that the problem with valve float isn't there. It doesn't happen unless you have high lift cams, or are spinning the engine way too fast

I plan on running an 8k redline on my built engine with solid lifters and the stock turbo cams, provided that power isn't dropping off drastically by then. If it does, I guess it's time for a new intake manifold and cams

Are individual throttle bodies realistic with a turbo for something like this?

[boostdoctor]

Boost Doctor my post is not a "theory". Hydraulic lifters pump up when the valves float, there is no longer any spring pressure on the lifter. You actually lose compression on a few cylinders when this happens and often the motor won't start after, until the lifters bleed back down. They don't come apart they just try to "adjust".

This is extremely common with the 16v heads as used on redblocks, stiffer valvesprings cures it.

You can potentially make lifters collapse but that's a different issue. With direct-acting valve trains at least(none of these motor have pushrods of course), the end of the valve stem is no longer being pressed against the tappet by the valvespring, so the tappet tries to expand to meet it and therefore ends up being too extended and it hold the valve open.

Regardless this is confusing the issue, since the hydraulic lifters are fine for 99.9% of people here. The only time I would see an issue is with hot cam like Russ and JC have said. I am running early 960 cams to 7600rpm with no issues. They don't collapse above 7000rpm.

Well I guess "theory" wasn't a proper word choice.

Anyways...the height of the lifter when the motor is running at normal rpm's is it's natural height. When the lifters "pump", the plunger(or tappet as you call it) is extending out of the lifter body. A retainer clip in the bottom of the lifter body would cure this problem. Retainer clips are standard in American pushrod motors. Also if adequate valvesprings cure the "pump" issue; what exactly is your concern with going to 8000rpm.

[ozzimark]

Are individual throttle bodies realistic with a turbo for something like this?

Depends on your budget. It's easier to just turn up boost to get more power. :lol:

[Johann]

I plan on running an 8k redline on my built engine with solid lifters and the stock turbo cams.

You don't have room for that.

M56H will go 121 mph in 3rd gear red line, M56L 135 mph... ;)

[ozzimark]

Minor details.

I know it's not necessary, or practical, I just want to see how the engine behaves when spinning that fast. Just like how making a VVT controller is probably a waste of time, but I want to see what I can get out of it if I do :)

[Captain Bondo]

Hahaha this is way OT now.

Thanks for the insights all! :)