DOHC or QOHC?

ruchi · Post by **ruchi** » Mon Mar 22, 2004 3:06 pm

I was intrigued to read in the recent Hot4s magazine (#108, with all the FTOs in it), that while most of the cars were listed as having Quad Cams at least one was listed as being Double Over-Head Cam (DOHC).

I thought the the FTO had Quad Over-Head Cams (QOHC), yet all the FTO brochures and Technical manuals list it as being DOHC.

I was under the impression that the FTO had two camshafts for each bank of the V. So there was a normal camshaft and a MIVEC camshaft for each set of 3 cyclinders, making it a total of four (quad).

So is it a DOHC or a QOHC? If it is a QOHC why do Mitsubishi call it a DOHC in all there brochures and technical manuals?

Anyone able to shed some more light on this?

scracy · Post by **scracy** » Mon Mar 22, 2004 3:34 pm

Ruchi it depends on the manufacturer as to which terminology they use.Toyota always qoute their DOHC v engines as quad cam since each bank of 3 cylinders has 2 cams.Its more of a marketing ploy than anything else.In the case of our cars either quad cam or dohc is correct.Obviously mitsubishi have chosen to state the later.Essentially it means the same thing.

The fact that the mivec engines have 2 sets of lobes on each of its total of 4 camshafts doesnt distinguish it as being a quad cam engine.The fact that it has dual DOHC since it is a V6 does. Hope this makes sense.

dannyboyau · Post by **dannyboyau** » Mon Mar 22, 2004 3:43 pm

it is a quad cam engine, meaning it has four cam shafts in total.

but there is only 2 cam shafts on each head so it is a double over head cam = DOHC

just to elaborate a bit more we will look at the wording for DOHC

double ( as in 2 ) over head (as in on top of a single head ) Cam ( as in camshaft

If it was QOHC it would be saying that the one head had 4 cam shafts.

You will often find that any V engines with DOHC will be referred to as a Qaud cam engine.

And the cam shafts are 1 as the exhaust and 1 as the inlet, on each head both camshafts have the normal lobes and the mivec lobes on them.

And it is just a bit to hard to explain how they work with out being able to show it to you.

dannyboyau · Post by **dannyboyau** » Mon Mar 22, 2004 3:50 pm

sorry scracy i didn't see your answer

didnt mean to repeat what you had said

i need to type quicker

ruchi · Post by **ruchi** » Mon Mar 22, 2004 5:24 pm

dannyboyau wrote:And it is just a bit to hard to explain how they work with out being able to show it to you.

No need to explain cams dannyboy, I understand how they work, it was just the mismatched terminology I was trying to clear up.

Thanks for the clarification guys.

So it has four cams (Quad Cam) but each head only has two cams over it (Double Over-Head Cam / DOHC).

So, to say that the FTO has a quad cam engine would be correct, but to say it had a quad over-head cams (QOHC) would actually be wrong, as each head only has two cams over it and as such is a double over-head cam (DOHC).

* Quad Cam [CORRECT]
* Double Over-Head Cam (DOHC) [CORRECT]
* Quad Over-Head Cam (QOHC) [WRONG]

In re-reading the article, I can see that I mis-read it, it lists them as being Quad-Cam, not Quad Over-Head Cam. My Fault! oops

But hey, we clarified something in the process, which is good!

dannyboyau · Post by **dannyboyau** » Mon Mar 22, 2004 10:32 pm

ruchi wrote:
dannyboyau wrote:And it is just a bit to hard to explain how they work with out being able to show it to you.

No need to explain cams dannyboy, I understand how they work, it was just the mismatched terminology I was trying to clear up.

Sorry didnt make that comment clear enough.

I meant how the mivec works. as the it is the same cam shaft that has the normal lobes and the mivec lobes right next to each other. And there is actually a hydraulic lifter that is operated by oil pressure that engages a differant part of the roller rocker assembly to switch between the two cam lobes, this is all electronicly controlled.
so when there is an electrical signal sent the oil is then directed into a hydraulic lifter which then engages the part of the roller rocker assembly which is running on the mivec lobe so that it then is the dominate part of the roller rocker assembly opening the valves.

Well as i said before it would be much easier to show you how the mivec works then to explain it.

ruchi · Post by **ruchi** » Tue Mar 23, 2004 12:12 am

I've seen a picture of the cams from the technical service manual, so I can picture what your talking about.

So rather than there being a MIVEC and non-MIVEC camshaft, there are MIVEC and non-MIVEC lobes / cams on each camshaft and it just moves the camshaft left or right to engage either the MIVEC or non-MIVEC ones.

Have I understood correctly?

dannyboyau · Post by **dannyboyau** » Tue Mar 23, 2004 1:09 pm

So rather than there being a MIVEC and non-MIVEC camshaft, there are MIVEC and non-MIVEC lobes / cams on each camshaft = correct

it does not move the camshaft sideways at any time this is impossible

an electrical signal is sent, the oil is then directed into a hydraulic lifter which then engages the part of the roller rocker assembly which will then connect with the mivec lobe so that it then is the dominate part of the roller rocker assembly opening the valves.

ruchi · Post by **ruchi** » Tue Mar 23, 2004 3:25 pm

cool. understood. thanks.

G_A_V · Post by **G_A_V** » Tue Mar 23, 2004 11:24 pm

any idea how the non mivec, cams differ ?

dannyboyau · Post by **dannyboyau** » Tue Mar 23, 2004 11:29 pm

G_A_V wrote:any idea how the non mivec, cams differ ?

differ from what

G_A_V · Post by **G_A_V** » Tue Mar 23, 2004 11:33 pm

well what would be the difference with the mivec system to he non-mivec system ??
I though all cam systems were timed

ruchi · Post by **ruchi** » Tue Mar 23, 2004 11:34 pm

Are you refering to the cams in a GR or the lobes in the GPX which are used below 5500rpm?

dannyboyau · Post by **dannyboyau** » Tue Mar 23, 2004 11:39 pm

G_A_V wrote:well what would be the difference with the mivec system to he non-mivec system ??
I though all cam systems were timed

do you know how a cam shafts works ?

could you explain what you mean by timed

Do you understand how the internals of a over head cam engine works ?