What the differences between different types of engines?

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Viper007Bond

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One question per thread and please make the thread titles more descriptive from now on. Thanks. :)
 

SiR_dude

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DOHC stands for Dual Overhead Cam. SOHC is Single Overhead Cam. Cams are lobes (shaped something like a teardrop) mounted on a shaft. As they rotate, they open and close the valves (exhaust and intake valves). DOHC engines have two camshafts, one for the intake, and one for the exhaust valves. SOHC engines have just one shaft which control both. The shape of the cam is extremely important in how you want the engine to develop power.

Here are HowStuffWorks links on cams:

Dual Overhead Cams

And an animation:

 

CanadianLoonie

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Okay, I got a similiar question...

Recall that back in Series 4-Episode 1, when JC was reviewing the Lotus Exige...he mentions something about that Toyota engine having two cams..."one for fuel economy and one for power" and how when it's over 6200rpm it switches the engine power to the power cam to "get evn more" power.

So what was he talking about?
 

Jostyrostelli

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VTEC stands for Variable Valve Timing and Lift Electronic Control.
I know it has something to do with RPMs. The valves are open shorter @8.000rpm than they are @ 2.000rpm. So when revving the engine to 8.000rpm the fuel is not being burned as efficient as it would be @2.000rpm. The VTEC system can change the Valvetiming somehow so the valves open and close at the exact right times.

Have to do some rechearch on this (Just bought study Carmechanic, I now have LOTS to learn and read...when I have time...I'll share ;))
 

bone

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OK, some explanation:

first, to get rid of some misunderstanding, the animation posted, is a SOHC, not a DOHC like the link would suggest.
SOHC:

DOHC:


the reason why merc used SOHC for so long is:
1) there's nothing wrong with it
2) it costs lots of money to develop DOHC
3) DOHC is harder to adjusts

why switch to DOHC:
1) more adjustement possible
2) you can change the intake without touching the outlet (impossible with SOHC), resulting in more power, but will break down sooner

now, anyone heard of pushrods? has also sth to do with it
imagine a V8, with single cam. the camshaft is lying in the middle of the cylinders (lower than the valves --> no overheaded), and needs specials arms (pushrods) to reach the valves, which are on the outside of the cylinder
http://static.howstuffworks.com/flash/camshaft-pushrod.swf

so you can have a V8 not OHC, with 1 camshaft, but with pushrods, you can have a V8 SOHC, with 2 camshafts, or a V8 DOHC (=4 camshafts), without pushrods. i never heard of a V8 with 2 cams and pushrods

VTEC has actually nothing to do with SOHC or DOHC, you can as easily have an SOHC VTECT as a DOHC VTEC. a VTEC engine, has 1 camshaft extra, this one isn't used below 4K RPM, abover these RPM, due to a spring, this cam is activated, and opens the intakevalves a fraction of a second longer, allowing more mixture in the cylinder, resulting in more power.

VVTI on the other hand, is again sth else. as your RPM climb, your cylinders move faster, which results in the cam turning faster, resulting in the valves being open for a shorter time. VVTI rotates the cam a few degrees, allowing the intake valve to open sooner, letting more mixture in the cylinder.

PS: porsche combined VTEC and VVTI, they have both
 

woodchuck

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Mercedes-Benz has been using DOHC since at least 1972.
Here's an M110 Mercedes-Benz engine:

Technical drawing:

DOHC:
 

andyhui01

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bone said:
VTEC has actually nothing to do with SOHC or DOHC, you can as easily have an SOHC VTECT as a DOHC VTEC. a VTEC engine, has 1 camshaft extra, this one isn't used below 4K RPM, abover these RPM, due to a spring, this cam is activated, and opens the intakevalves a fraction of a second longer, allowing more mixture in the cylinder, resulting in more power.

VVTI on the other hand, is again sth else. as your RPM climb, your cylinders move faster, which results in the cam turning faster, resulting in the valves being open for a shorter time. VVTI rotates the cam a few degrees, allowing the intake valve to open sooner, letting more mixture in the cylinder.
can you explain how MIVEC works or is it just the same way as VTEC... btw has anyone heard the engine when the VTEC comes on... the sound is amazing and it feels like some turbo just kicked in giving you extra boost :D
 

SiR_dude

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andyhui01 said:
... the sound is amazing and it feels like some turbo just kicked in giving you extra boost :D
:twisted: :twisted: :twisted:






+






= AWESOME!!!!!

Well, the "feeling" deepends on the shape of the cam lobe. With my car, Honda engineered it for a smooth transition, so there's no noticeable jerk when VTEC engages (Bone explained it pretty good). However, in wet weather, I can be in second gear, mash it without losing grip at 3k, but about 5400 I'll lose grip becuase of the power surge. With the Acura Integra Type R, the cam lobe is more aggressive, and thus VTEC engagement will push you into the seat more.

And yes, the sound gives you goosebumps :mrgreen: :mrgreen:
 

andyhui01

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I sat in a Honda Civic with a B18C engine (Integra Type R 1.8l) engine... you know for sure that the vtec kicked in... after I get bored of turbo cars... I would look for a vtec car... do you know how the i-vtec works... on the new Honda CR-V... I floored the car and I couldn't feel the vtec kicking in at all :shock:
 

Dark_Templer_102

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VTEC is like 2 camshafts and one just kicks in for higher reves and ones for lower

Mercs are currently useing SOHC for most cars

Go to mbusa.com

Stats for S500 Engine and Drivetrain
Engine 4,966-cc SOHC 24-valve 90? V-8. High-pressure die-cast alloy cylinder block. Alloy heads.
Net power 302 hp @ 5,600 rpm
Net torque 339 lb-ft @ 2,700 - 4,250 rpm
Compression ratio 10.0:1
 

SiR_dude

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andyhui01 said:
I sat in a Honda Civic with a B18C engine (Integra Type R 1.8l) engine... you know for sure that the vtec kicked in... after I get bored of turbo cars... I would look for a vtec car... do you know how the i-vtec works... on the new Honda CR-V... I floored the car and I couldn't feel the vtec kicking in at all :shock:
The B18C is a great engine. You couldn't feel the VTEC engagement in a CRV because Honda designed it that way. It's an SUV for families, not a sports car - who wants a noticeable power surge in a vehicle like that? Honda designed it for a smooth transition. It's not becuase of the iVTEC, it's cause of the type of vehicle, and the market it's aimed at - Honda didn't want to give kids in the backseat whiplash. iVTEC is just Honda's next generation of VTEC engines.
 

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VTEC is an on-off switch, below 4K RPM, there's nothing, above it's activated. I-VTEC isn't. The I in I-VTEC stands for intelligent and it's a smooth transmission. the length of time the valves are open get's longer as your RPM climb, so you'll never feel it kicking in.

i prefer VTEC, but overall I-VTEC is better

my favorite honda-engine is the VTI. it's a DOHC-VTEC engine, but with 5 valves/cylinder (like the VW 20v)
 

andyhui01

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I think VTEC gets you a harder kick (all the power comes at once)... iVTEC smoothly gives you the power... so being a person who likes the feel of the turbo boost coming on should prefer VTEC over iVTEC
 

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in both cases you have to rev the shit outta them to get the full power, i think! right? VTEC's torque on low rpms are not much and they don't gooo if the rpms drop
 

bone

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idd, that's why the S2000 is a pain in the ass at low RPM
 

SiR_dude

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andyhui01 said:
I think VTEC gets you a harder kick (all the power comes at once)... iVTEC smoothly gives you the power... so being a person who likes the feel of the turbo boost coming on should prefer VTEC over iVTEC
Not really true. My car utilises the VTEC technology, and there's no kick - it's still a smooth transition. The kick you feel is just the difference in the change of cams and timing.

logo said:
in both cases you have to rev the shit outta them to get the full power, i think! right? VTEC's torque on low rpms are not much and they don't gooo if the rpms drop
Yes, that's the whole point of VTEC. It lets you have a low-torque, granny-driving range that's fairly reasonable on fuel economy, but if you want to have fun, just keep the pedal down. It's true that low end torque is minimal, but believe me, for daily driving, I see no need to rev above 4000 in my car. And when I want to go, it's just a blip of the throttle, a quick downshift, and 1.6 litres singing at 8000 rpm :twisted: :twisted: :twisted:

It's a lot of fun :mrgreen: :mrgreen:
 
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