I see very little serious tuning done on VVC engines (I mean with the VVC mechanism intact). Could anyone explain to me what the problem(s) is/are when you want to get it over say 200bhp?
I am no expert, but researched this for my VVC engine. The answer is fairly complex but involves several key aspects.
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The VVC mechanism and cams etc provide a good balance between torque and power across the rev range. They are not designed for very high peak power - they provide neither the valve lift or duration of some of the “hotter” cams that are available.
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The pistons (S2 VVC), although better than the std pistons are not really designed to cope with either very high rpm (7300 - 7500 about maximum safely) or power much over 180 bhp.
The std inlet plenum won’t get you much over 180 bhp.
To get really high power out of a 1.8 (say >200 bhp), you will probably need cams that provide adequate duration and lift, possibly solid lifters rather than hydraulic tappets (although hydraulic still possibly OK at 200 bhp I would think) direct to head throttle bodies and a rev limit well above the 7200 odd of the VVC. That in turn requires a strong enough bottom end - forged pistons, decent rods etc.
175-180 is possible on a std VVC bottom end, std plenum, std ECU, with a decent port some fettling of the exhaust cam and retaining the VVC mechanism. Beyond this requires a lot more effort and money.
Thanks for your reply Shangani. Still, almost all the reasons you give apply to a non-vvc as well and the conversion to solid lifters shouldn’t be too expensive either, right? Can’t see that being a requirement for the VVC system to work?
I could think of some others reasons though:
1 Less demand, since the base engine already produces more power than a standard K
2 VVC advantages of better low down torque, less emissions and fuel use are perhaps not as important for people looking for a highly tuned K
3 6kg (right?) weight penalty pretty high up in the car.
Sounds plausible?
Bit more far-fetched:
4 Proper cam profile design is more complex when using the VVC mechanism?
The VVC cam profiles themselves are quite normal I think. Its just that they are pressed onto shafts in an unusual way.
The torsional forces caused by increased lift and duration will destroy a VVC mech in the same way running them above 7300rpm does with the std profiles. All the replacement profiles for VVC heads (okay bar the reground Piper exhaust cam which is rare) require you to remove the VVC mech anyway.
The VVC has pretty much the same bottom end torque as the std 1.8 MPi engine. The main benefit of the VVC lump is that the VVC head gives you bigger valves to work with. Saying that, some of the Powertrain engineers did do a after hours Caterham roller barrel throttle conversion which made 185 BHP apparently. I bet that would be quite pleasant to drive?
heres a turbo one
I’d echo the above responses, the VVC inlet profile although extending to 290 degrees, does not have the area under the lift curve that you would expect because the valve acceleration is quite low. Couple this with a relatively short duration exhaust cam and you have limited potential.
The VVC mechs are pretty much on the edge of reliability in the standard installation, much higher RPM would push them too far.
I have been involved with a couple of VVCs that had much more radical exhaust cams, throttle bodies and lightly ported heads, the best of these running on an Emerald made just over 200BHP.
Tweaking the VVC is a well trodden path, i have been involed with around 50 upgrades that retained the VVC mechs and s similar number that have converted to solid cams.
Retaining the VVC mechs , upgrading the exhaust cam and porting the head can push BHP to around 180-185, adding TBs/ECU at this point would probably see another 10-15BHP or so, but then the pistons will always be on the edge of reliability.
The profile design for the VVC isnt that much more complex, the variable element is handled purely by the mech slowing the cam down during the open phase and speeding it up during the latent/close phase. However increasing the valve acceleration would probably push the VVC mechs beyond their comfort zone, when one fails the result is not pretty.
The Caterham RB conversion sounds good, but my direct experience is of several upgraders returning their upgrades because of serious drivability issues connected with the retention of the stock ECU which uses MAP to determine load.
Dave
heres a turbo one
337hp, that’s quite serious horsepower. I just want to understand the limitations of the vvc system though, but thanks.
The VVC cam profiles themselves are quite normal I think. Its just that they are pressed onto shafts in an unusual way.
The torsional forces caused by increased lift and duration will destroy a VVC mech in the same way running them above 7300rpm does with the std profiles. All the replacement profiles for VVC heads (okay bar the reground Piper exhaust cam which is rare) require you to remove the VVC mech anyway.
Ok, thanks for the explanation.
The VVC has pretty much the same bottom end torque as the std 1.8 MPi engine. The main benefit of the VVC lump is that the VVC head gives you bigger valves to work with. Saying that, some of the Powertrain engineers did do a after hours Caterham roller barrel throttle conversion which made 185 BHP apparently. I bet that would be quite pleasant to drive?
I reckon so. About the bottom torque being comparable to a 1.8 mpi, well that engine is not tuned for high rpm power so it does not have cam profiles that compromise filling rate at lower rpm for the sake of more air at very high rpm, right?
I’d echo the above responses, the VVC inlet profile although extending to 290 degrees, does not have the area under the lift curve that you would expect because the valve acceleration is quite low. Couple this with a relatively short duration exhaust cam and you have limited potential.
The VVC mechs are pretty much on the edge of reliability in the standard installation, much higher RPM would push them too far.
Ok thanks, it’s a pitty though since for a normal road engine, the higher it revs the more it will profit from a variable valve system, right? Possibly the reason why Powertrain were so involved with that new valve actuating system. Could also imagine the capacity increase they were working on would have helped, giving more power without having to increase the revs forcing them to drop the VVC system.
I have been involved with a couple of VVCs that had much more radical exhaust cams, throttle bodies and lightly ported heads, the best of these running on an Emerald made just over 200BHP.
Tweaking the VVC is a well trodden path, i have been involed with around 50 upgrades that retained the VVC mechs and s similar number that have converted to solid cams.
Retaining the VVC mechs , upgrading the exhaust cam and porting the head can push BHP to around 180-185, adding TBs/ECU at this point would probably see another 10-15BHP or so, but then the pistons will always be on the edge of reliability.
The profile design for the VVC isnt that much more complex, the variable element is handled purely by the mech slowing the cam down during the open phase and speeding it up during the latent/close phase. However increasing the valve acceleration would probably push the VVC mechs beyond their comfort zone, when one fails the result is not pretty.
The Caterham RB conversion sounds good, but my direct experience is of several upgraders returning their upgrades because of serious drivability issues connected with the retention of the stock ECU which uses MAP to determine load.
Dave
Ok thanks for all the detailed answers. Guess then if there ever would be a new production NA K-series with say more than 190bhp, it would have to have more than 1.8l capacity and/or a different variable valve system.
I did a modification of a VVC engine for a customer who did not want to spend a lot of money and got 195 bhp with these changes:
Block with pistons 82.50 mm
VVC piston head with the valve seats open to 29.6 mm inlet and 25.3mm exhaust
Retimmed exhaust cam
Compression ratio of 11.7/1 in the piston head with spark plug denso IK24
Crank in arrow
Blue injector of 4 holes
Throttle bodie of 56 mm open to aproxx 58/59 mm .
Flywheel of PTP
Thermostat of 71 degrees
Exhaust complete without CAT of janspeed of 42 mm big bore
ECU Emerald
Regulator fuel pressure
Regards
Hi Vincente,
That is pretty much consistent with the outputs seen from 1786cc versions of around 1835-185BHP with similar specs.
Dave
Hi Dave
Yes, but I said bad the result of the power, because in Spain we measure with c.v., equivalent to a little more than bhp.
Are 195 c.v., equivalent approximately to 201/203 bhp.
I would like teach to you, my 2.0 k, so that you could be measured to check the quality of materials to try to give a more specific opinion on it, because I have the impression that you are not very much in favor of the 2.0 k engines.
Sorry, we are so far away from each other.
All the best
Vicente
Hi vincente,
I thought the CV was the same as a PS and a little less than a HP being .9863HP (.7355KW) . 195CV is therefore around 192BHP.
I would certainly welcome the opportunity to see the block conversion but i am not convinced on a longer stroke version of the engine.
Dave
Hi dave
Yes you have reason, I made the conversion to the setback.
I hope that some day you can see or have one in your hands.
Referring to the conversation the other day, my crank 2.0 k, has the con rod with a length of 132 mm between centers, very little difference with the standart of 1.8 k.
I am convinced that if you see or use my 2.0 k, you change of opinion.
Regards
Vicente
Hi vincente,
Rod angle is not just affected by rod length but also the stroke of the crankshaft. With a 93mm stroke the rod angle will be over 26 degrees and the rod ratio 1.41 against an ideal rod angle of around 19 degrees and ratio of 1.75.
I’m happy with a bore increase, but not really with a stroke at that level.
Dave
Hi Dave
Unfortunately, as you already know, few things are perfect mechanical, provided there is usually a percentage of things that are not entirely as he would like to oneself.
But if I tell you, that the stroke of my crank 2.0 k, is less than 93 mm, precisely, I think that the designers chose a shorter stroke, to try to alleviate those who say in your article on the grades and the ratio.
My crank 2.0 k, has a stroke of approx 91.7 mm.
The designers my crank 2.0 k, I was told that it was better not increase the stroke more than this, because so would have the possibility to climb to 8,500 smoothly and would have other advantages besides.
I think now, that these advantages to those that addressed, are what would you say about the grades and the ratio.
The designers put this example to me, about of the Alfa Romeo 155/156 of WTCC, where a cylinder capacity of 1965 c.c, I seem to remember, were the most competitive and with a power equal to or greater than the engine 1998 c.c.
Regards
Vicente
Hi Vincente,
I’m sure the 2 litre is a fine bit of kit, but for most upgrades, retention of the stock crank and rods is a powerful persuasion when you consider the cost of a replacement crank and rods for just 100cc extra, the 1886 conversion makes more economic sense for most owners.
The block and piston combination is the most interesting from my/my customer’s perspective(s).
Dave
Hi Dave
Yes, that is clear.
If you keep your crank and con rod of 1.8 standart and only buy the pistons of 82/82.50 mm and the block, it will always be cheaper.
These 100 c.c additional can provide 15/18 c.v. approx, and depends on other factors, such as cams, or TB,S that can be more c.v. or not.
If you need one block for you prepared for pistons 82.50 mm and pistons of 82.50 mm, tell me and I make a good price.
Regards
Vicente
Hi Vincente,
It is probably better for any continued discussions to take place via email rather than on the forum.
Dave
Hi Dave
Ok, I thought you liked exchanging views, If I bother you with something, sorry.
Regards
Vicente
No, no Vincente,
You are not bothering me, it’s just that the discussion was becoming more pointed towards our requirements rather than the general audience…
Dave
Hi Dave
Ahhhhhhhhh, ok
Regards
Vicente