Quad Valve Heads
Discussion
Arao Engineering has been doing them for ages (and recently put their prices up). I enquired a couple of years ago but Russ Arao said that they hadn't developed a head for the LS1 at the time. I wonder if they have now ? Sounds just the sort of thing to fit on an LS7, I reckon their C2 specifcation head is just right for the job for when you get bored with your straightforward Lingenfelter cam...
Not sure how well that'd go in a Vette, pretty much all 4 valve designs are double overhead cam, which comes with a significant increse in head height, which on a V8 means overall width is increased, not an easy thing to accomodate when the engine sits between two substantial frame rails. Hence they couldn't (as GM originally wanted)design some bolt on heads for the SBC when working up the ZR1 design, hence all new (at the time) LT5 engine.
They use Y-shape forked rockers worked by pushrods rather than an OHC design so I don't think there's much difference in head height. Connecting the intake ports to the standard plenum might be more of a problem. If the engine has been dropped an inch or two in the C6 Z06 due to the dry sump then I presume there'd be a bit more vertical space between the heads and the bonnet to play with, don't know about horizontal space to the side of the engine bay though.
Looks like an interesting design, although they're talking rubbish quoting valve area as a benefit in 4V designs - it's actually the opening circumference that's the benefit, for the same lift, more, smaller valves actually yield a larger flow area, which is not shaped like a circular disc but more a curved rectangle.
I don't think the dry sump reduces engine height by very much, half inch maybe. ls2,6, sumps are pretty shallow as is.
I'm not sure the 4 valve head would really catch on as the 2 valve head is supposed to be pretty good and will be good for mid range grunt. I'd expect the 4 valve head to suffer lower down. Still, for those with money, a blower, rods and 4 valve heads may be just the ticket
and a custom intake would get around any change in port heights.
Boosted.
I'm not sure the 4 valve head would really catch on as the 2 valve head is supposed to be pretty good and will be good for mid range grunt. I'd expect the 4 valve head to suffer lower down. Still, for those with money, a blower, rods and 4 valve heads may be just the ticket
and a custom intake would get around any change in port heights. Boosted.
Hmm, I thought that the main reason for dry-sumping an engine was to enable it to be mounted lower in the chassis thereby dropping the centre of gravity and improving grip. I remember LJK Setright saying that a 1" drop in the CG of a car was the equivalent of making its track 6" wider. Reduced oil surge was a secondary benefit (and can be helped by fitting baffle plates in the sump). Probably depends on whether you speak to a chassis engineer or a motor one as to the opinion you receive on what the primary reason is !
Explanation of dry sumping by NCM and GM performance on the links below,
www.corvettemuseum.com/specs/2006/index.shtml
www.gmhightechperformance.com/features/0505htp_2006_z06_corvette_feature/
www.corvettemuseum.com/specs/2006/index.shtml
www.gmhightechperformance.com/features/0505htp_2006_z06_corvette_feature/
Haven't read the link, but another reason for dry sumping is to reduce the windage losses in the engine (that's the energy lost to thrashing about the oil/air in the free space above the oil level in a wet sump) - with a dry sump much of this is actually sucked out of the crankcase by the suction side of the dry sump pump.
franv8 said:
Not sure how well that'd go in a Vette, pretty much all 4 valve designs are double overhead cam, which comes with a significant increse in head height,
and added weight with the double overhead cam arrangement. The Corvette division of Chevrolet has spent countless hours increasing performance through weight-reduction. And the LS7 is their crowning achievement; 505hp, with a non-blower engine and conventional single cam 2v/cyl.
Of course the states have the luxury of going to larger displacement engines, due to a lower petrol price than what's seen in Europe.
Edited by Mike Mercury on Wednesday 22 November 03:03
Mike Mercury said:
franv8 said:
Not sure how well that'd go in a Vette, pretty much all 4 valve designs are double overhead cam, which comes with a significant increse in head height,
and added weight with the double overhead cam arrangement. ]
There is no double overhead cam! You may get a slight weight increase from the double rocker systen but your talking a couple of pounds at the most!
G
Mike Mercury said:
Of course the states have the luxury of going to larger displacement engines, due to a lower petrol price than what's seen in Europe.
Yes, but have you compared the fuel consumption out of this big engine compared to similarly powered, smaller blocks? It's usually the same, or sometimes better!
No replacement for displacement ;-) [or turbos, quad OHC cams (... er my own Corvette ignores that bit
]c4koh said:
Mike Mercury said:
Of course the states have the luxury of going to larger displacement engines, due to a lower petrol price than what's seen in Europe.
Yes, but have you compared the fuel consumption out of this big engine compared to similarly powered, smaller blocks? It's usually the same, or sometimes better!
No replacement for displacement ;-) [or turbos, quad OHC cams (... er my own Corvette ignores that bit
]you have a point there; but I do believe the MPG (KPL ???) ends any similarity once you start driving hard.
Another drawback to DOHC engines is added internal friction and increased rotational mass. All are things (including the increased weight) that take away some of the added HP that is originally gained with the DOHC 4v per cyl design.
Mike Mercury said:
Another drawback to DOHC engines is added internal friction and increased rotational mass. All are things (including the increased weight) that take away some of the added HP that is originally gained with the DOHC 4v per cyl design.
You're not listening (or rather, reading). This is NOT a DOHC design. It still uses one cam in the V. It's just that it actuates 4 valves per cylinder.
I would like to see some real world performance and durability results on this design. It would probably be easier to bolt a supercharger or LPE's twin turbo set up...
Actually Mike, for the sort of engine (size-wise) the Corvette engines don't do as bad as you'd think for fuel over here. My old L98 will do low 20's (if gentle!), whereas an LT1 will manage high 20's (like 27 mpg) - these are UK mpg, which are 20% larger due to imperial gallons. By comparison, my 1.6 MX-5 does about 27mpg, with a motor a third the size!
And for all those watching, that is a 16V DOHC design...
What is often missed with multivalve designs, is that as a standalone set-up they have poor gas velocities at low rpm's, hence mostly won't pull very effectively from low revs (my old VW Corrado wouldn't get out of bed under 4000rpm), but Lotus (and I suspect it was a result of their technical colaboration with Toyota, who also used to do it on the 3S- family of engines, Celicas and MR2's 2.0 16V) designed a butterfly valve onto the LT5 in every other intake port, thus restoring much of the low speed tractability and combustion effectiveness by only running air through one intake valve at low speeds.
In fact, they used a different cam profile on the other intake valve, that was optimised for high rpm breathing. Think of it as another way to get that VTEC effect...
This quad valve set up looks interesting, however I suspect it puts more stress onto the pushrods and lifters, it's got to require more pressure to actuate the extra valves and rocker componentry.
And for all those watching, that is a 16V DOHC design...
What is often missed with multivalve designs, is that as a standalone set-up they have poor gas velocities at low rpm's, hence mostly won't pull very effectively from low revs (my old VW Corrado wouldn't get out of bed under 4000rpm), but Lotus (and I suspect it was a result of their technical colaboration with Toyota, who also used to do it on the 3S- family of engines, Celicas and MR2's 2.0 16V) designed a butterfly valve onto the LT5 in every other intake port, thus restoring much of the low speed tractability and combustion effectiveness by only running air through one intake valve at low speeds.
In fact, they used a different cam profile on the other intake valve, that was optimised for high rpm breathing. Think of it as another way to get that VTEC effect...
This quad valve set up looks interesting, however I suspect it puts more stress onto the pushrods and lifters, it's got to require more pressure to actuate the extra valves and rocker componentry.
godzilla said:
You're not listening (or rather, reading). This is NOT a DOHC design. It still uses one cam in the V. It's just that it actuates 4 valves per cylinder.
I would like to see some real world performance and durability results on this design. It would probably be easier to bolt a supercharger or LPE's twin turbo set up...
I and a few others had settled in on a discussion about run-of-the-mill DOHC designs.
Didn't mean to hijack the thread.
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