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FAO The Captain
- Thread starter ChavyBoy
- Start date
sorry Chavvy no I didnt get it ??.
try again, captainslarty@ntlworld.com
Joe
Anyway, been reading alot of reviews on the Civic Type R and they all say it has a really crap bottom end acceleration. Now what M.C. said the other day about his Nova being pish bottom end and following through with a good mid range punch made me think.
M.C. said he had a different cam and thats what made the launch speeds a bit poop which maybe the same case as the CTR.
Now if we get Nick Hill to make up a fast road cam this may slow down the initial launch speed but give better mid range punch and top end punch. Would the VVT help with the pish bottom end of the fast road cam at all ?
Hi M8..
unfortunately, you cant just change the cam without looking at everything else.
Tomorroy I am testing the cams n the 172 and the turbo unit.. I have made a jig to allow the protractor and dial gauge to be set up and can measure lift - (At the valve) in 2 degree increments..
from there, we should have a good idea what the lift, ramp and duration is.
knowing that, it may be possible to run some simulations through the computer to see what types of benefit, if any, can be easily gained.
the ctr hasnt really got a crap bottom end accel.. its just that the vvt is pretty bloody noticable.. unlike a 172..
the cams in the 172 are pretty wild now, but may benefit from overlap to make use of the exhaust and inlet tuning already in place by mr reno..
the bottom end accel in the 172 isnt bad anyways ??..
ps, what was that about the diesel turbo crank m8 ??.
Joe.
oh,, forgot to mention, the vvt may be of some use for idle..... but it depends on the cam profile..
Joe
Captain does the VVT only work at 1200rpm cause my thoughts maybe if you had a fast road cam thus giving you a lumpy tickover maybe you could re-program the unit that moves the cam to allow for this ?
As to the diesel crank didnt you say it was similar or the same as the 172 crank ?
Could you use the Turbo of the DTi clio in the 172 ?
mate, it came out bad.....haha, wasnt throwing an insult!
but i guess you could define a fast road cam as that.
But there is much more to a cam then duration. Lift, ramp, symmetry and LCA (Lobe Centre angle- the angle between the inlet and exhaust lobe).
basically, the search for power is not much more than trying to obtain better cylinder filling at as high an rpm you can. The more air you can process, the more fuel you can burn. SO if you achieve say 100% VE @6000rpm, then why not work on upping that to 7000 then 8K rpm.
all my race engines concentrated at acheiving as high a VE at as high an rpm as possible....8K rpm has twice as many burn cycles as 4K rpm.
yeah, volumetric efficiency.
haha, 300% more...were talking serious stuff then haha!
i have no idea on figures!
but 300% more air, 300% more fuel.....to keep the same ratio.
but then i suppose capt will tell us that there are other factors..
im also wating for him to tell us about pre-ig and detnation!
Lads,
I dug out an old CCC over the weekend. They had an article on cams, and how to choose what is suitable for your engine, and how to set them up.
The point of interest was the overlap between inlet and exhaust. The amount of inlet lift on overlap. They basically said, that the greater the overlap, the more horse power, but youll have a rough idle, and youll loose low and mid range torque. Nothing new there you say, but that would explain the lack of difference in acceleration times between the VVT on and VVT off. With it on, youll get more power, less low down torque. With it off, youll get more low down torque and less power. On a 1/4 mile run, those two could even each other out. Did you try a top speed run? If the peak power is less, surely top speed would be reduced? Assuming youre not reaching the rev limiter of course. So VVT does help, although if it cut in higher in the rev range like the CTR, say 5k plus you might be able to benefit from the better mid to low range torque?
Does this make sense? It does to me.
yes, but increased overlap works at high rpm as the velocity of the air keeps pushing itself into the cylinder even on the compression stroke. @ low rpm, the mxture just excapes out the exhaust valve.
Caprt has done tests and VVT on is the same as VVt off.
and the whole point of VVT is so you keep the low end torque and the high rpm power by increasing overlap.
So VVT on should theoretically = good power @ low and high RPM. With it off, it should equal the same low rpm power and reduced high rpm power.
well, the stuff is correct, as dave is one of my idols and i have had a few chats with him at CCC action days.
anyway, from capts tests, t shoes that the VVt makes no diff to 1/4 mile times at all.....hes trying to figure out why its there at the mo....unles he has found out why already.
BTW, i got a star letter in CCC....dead chuffed if you couldnt tell.....
This is an area that we are looking at on the Nova. As I mentioned, we have silly peak power and poor low down torque. Its impossible to make a quick start. A few people use this engine for sprinting, and the engine tuners have been reducing the lift on overlap so that they can get off the line better with improved low down torque. We should be looking at this combined with trumpet length to try and adjust our problems.
I know the 1/4s were the same. My torquey 1.6 and the high bhp Nova run similar 1/4s but the power and torque curves are very different. All Im suggesting is that the drop in peak power is compensated for by the increase in torque. In theory the 1/4 might not be affected. If you ran a mile instead of a 1/4 the slight drop in peak power would probably hinder the acceleration at the higher speed, and reduce the top speed, and youd probably notice a difference. I reckon if this is the case, you could delay the activation of the VVT, and get the best of both worlds.
M.C.
afternoon guys.. wow !, this thread grew !!
ok, lets sorta sum up what we know of the 172 vvt and then look at cams in general.. ps Chavvy, I like yer thinking dood !!
Ok, the cam on the 172, as Ben rightly said, is already a fast road to Rally spec...
Put it in a normal non vvt head (Same volume and port size, shape, valve size etc) and it would either produce the same power exactly as the 172 but with a tractor idle .. or, you could alter the timing to obtain some compramise better idle but lose out on through the range power.
All the vvt does is, at idle, it retards the cam timing to obtain a good idle, as soon as you apply gas, it advances to its normal range - on or off.. no variation...
It also allows the cam to be retarded on overun to aid emissions..
Lift is constant, vvt does not, and cannot in this design, alter lift.
Mc, you are also correct in that it should effect power if not activated... it doesnt seem to.. although it needs to be tested on the rollers to see the actual results.
This is probably due to the little amount of advance that occurs, and the fact that, yes, it is probably shifting the power range but still remaining eminently drivable. more than likely screwing emissions though...
the 172 runs little overlap, as is common with many modern, emissions conscious engines, and the use of overlap is not a guranteed power trick, unless, you have suitable inlet and exhaust that can act as an extractor.. the gas velocity at high rpm will certainly do this to some extent. and, the 172 has a nicely designed induction and exhaust.
If your nova is 16v, then you can alter the amount of overlap by the cam phasing, not possible on a single cam without regrinding..
As for the use of vvt with longer duration / more overlap cams, yes, it would certainly be beneficial.
as for the setup of cams for, say, 1/4 miling, it is certainly possible in some applications to alter timing to move the power band, but you need a rolling road and time, and lotsa dosh to do it correctly.
Joe.
OH!
and looking at the new lagina 2ltr, it has the same engine, ill get the block No and whatever, but looking at it int he shoroom, its got the same head casting, dunno about internals, but its got the same VVt aswell. Just a diff set of manifold and injection system visable from the outside.
Will have to wait till one breaks down to have a look at the head.....how diff do you think it is? same casting but not cleaned up.....?
