Push rod flex - really?

[ChilliWhizz]

Apologies to others and original poster of the quote below (nicked from the S6 in a Chim thread)... We're all familiar with the second half of the quote below....RV8 cylinder heads valve sizes, restrictive etc etc but, ''flex in the pushrods and rocker shaft location-this has a HUGE effect on top end power'' Really? I'd like to know more about this, anyone got first hand experience or knowledge of it?

Just HOW much power might I be losing over 4k rpm because of my flexing push rods and rocker gear?? Or rather, how many extra missing horses will reappear when I fit stuff that doesn't flex? Does this non flexing valve train kit exist? Where can I get it?

These are the things I need to know

Marquis Rex said:

Other points of note are the fact that the valve timing does its own thing about about 4000 rpm due to the flex in the pushrods and rocker shaft location-this has a HUGE effect on top end power, an area where the undervalved Rover V8 struggles already- enlargening the capacity further will just boost low speed torque with little effect on peak power due to the restrictive nature of the cylinder heads- you’ll end up having to go to specially made Wildcat heads to get the top end back unless you’re particularly fond of the feel of a “diesel-esque” torque curve.

ETA: Hands up all those with a 'diesel-esque' torque curve

Edited by ChilliWhizz on Friday 17th January 14:27

[Alun450]

Its all very true, change gear earlier chilli, yes yes I agree who's selling the stuff,,

[TVR Beaver]

Have a word with SPEND .. last time I was at his gaff he was fitting what looked like 12mm dia push rods to Pascos new engine

now they won't bend

[Sardonicus]

TVR Beaver said:

Have a word with SPEND .. last time I was at his gaff he was fitting what looked like 12mm dia push rods to Pascos new engine

now they won't bend

Yep Spend uses bigger push-rods too but quite frankly when your in this territory your not running hydraulic cam gear anyway and were all just playing toy engines compared to Spend

[900T-R]

Mine tops out at 6,000 rpm and hits the 6,800 or so rpm limiter in the blink of an eye... good enough for an old school V8 on hydraulics. If you wanted to make 100 bhp/litre (N/A) like the new school of engines, granted but then again the heads are your real restriction (oh, and keeping everything together inside the block).

Don't try and fix what isn't broken (in the context of your car)... I'd much rather have some CNC-machined ally uprights with better front geometry that someone else will stand for should it go pear shaped...

[Alexdaredevils]

This is what im using, and so are a godzillion guys in the states pushing over 7k rpm with no issues

http://www.summitracing.com/dom/parts/cca-7638-16/...

[spend]

Push rods and locations are flexing judging by the frequent score marks on used pushrods.

The springs to on the rocker shafts allowing the rocker arms to move along the shaft could be a contributing factor.

I have made special rocker gear consisting of:

Pedestals made to my own design with outriggers from billet ally.

Spacers between rockers and spring shims to locate the rocker arms and retain oil pressure.

Roller Rockers note the correct offset @ seems like some RR don't even bother with the pushrod/stem offset!
Changed to oiling up the pushrods & head oil holes tapped with bungs screwed in.

Head pushrod holes opened to allow 7/16" dia Nascar pushrods
- (note not just a big hole drilled willy nilly but an oval cut mirroring the lateral rocking of the pushrods)

Block drilled so some drain back directly into front cover

All block valley polished & smoothed for drain back.

Cam splash guard fitted under valley gasket (screwed into block at front & rear)

Jesel Rocker adjusters fitted all round as an upgrade to the std Kenne Bell ones.

Solid Cam & lifters (followers) of course

Oil gallery link at rear of cam (bearings only draw from the one gallery!) and a tapping to allow pressure guage reading at rear of block

Stays across the heads at front & rear to keep block 'square' are made, but need to fabricate alternate ancilliary mounts. Any twisting in the block geometry (before slipped liners... but same idea) would have impact on valve timing so keeping everything in real life matching the mathematical model is tantamount.

Having said all that you need significant mods to the rest of the engine & induction before having to bother....

Just as important is the crank & cam...
Cam bearings & drive gear/chain
Crank balancing and damping ~ dont need much fore/aft twist/snapback in the crank to throw the rear cylinder valve timing out..
Requires good balancing & as good a damper as you can afford IMHO.

Maybe very esoteric, but essential if you want to reach high rpms (from the point of view that your average 6000 is FA)

Edited by spend on Friday 17th January 15:49

ETA: pic & stuff I had forgotten

Edited by spend on Friday 17th January 17:03

[Alex]

ChilliWhizz said:

ETA: Hands up all those with a 'diesel-esque' torque curve

XJ Flyer

[Podie]

You know what 'Rex does for a living, right?

[900T-R]

Podie said:

You know what 'Rex does for a living, right?

No one is disputing the facts, just the implications. From an engineering POV I would worry (and occasinallydo, in a constructive sort of way) about lots of things in our 15-20 year old TVRs before wasting any thought on the engine TBH.

[Alun450]

Some engine you must have there Alex, its going to be worth the wait by the sound of it!

Probably worth the wait just for the sound of it!

[ChilliWhizz]

Podie said:

You know what 'Rex does for a living, right?

Actaully, no! But as 900T-R states, nothing is being disputed here, it's a simple case of being hungry for knowledge

[Sardonicus]

spend said:

Push rods and locations are flexing judging by the frequent score marks on used pushrods.

The springs to on the rocker shafts allowing the rocker arms to move along the shaft could be a contributing factor.

I have made special rocker gear consisting of:

Pedestals made to my own design with outriggers from billet ally.

Spacers between rockers and spring shims to locate the rocker arms and retain oil pressure.

Roller Rockers.

Head pushrod holes opened to allow 7/16" dia Nascar pushrods
- (note not just a big hole drilled willy nilly but an oval cut mirroring the lateral rocking of the pushrods)

Just as important is the crank & cam...
Cam bearings & drive gear/chain
Crank balancing and damping ~ dont need much fore/aft twist/snapback in the crank to throw the rear cylinder valve timing out..
Requires good balancing & as good a damper as you can afford IMHO.

Maybe very esoteric, but essential if you want to reach high rpms (from the point of view that your average 6000 is FA)

Edited by spend on Friday 17th January 15:49

That is one RV8 I would like to hear on full chat Dave

[Alun450]

I'm with you there Chilli I just love it when there's even fatter push rods we can aspire to fit, its never ending and a joy to hear!

Anything that adds to the car without going to far off the page is alright by me!

[5.0ltr]

TVR Beaver said:

Have a word with SPEND .. last time I was at his gaff he was fitting what looked like 12mm dia push rods to Pascos new engine

Now that's something I would like to see....No not the push rods, but Pasco`s engine! Or the car, or the man himself...

[Hoofa]

Alun450 said:

Its all very true, change gear earlier chilli, yes yes I agree who's selling the stuff,,

Or just pull that carpet out that's stuck under the loud pedal

[SILICONEKID346HP]

I thought RV8 engines were simple ! it`s baffling