C Orndorff

iTrader: (16)

Well this is it. VTEC for all SOHC cars explained. Before you even read this I want you all to know that all figures are form both 1996-2000 Honda tech book and 2001-2003 Honda Tech book. I have a few pages scanned in form the books to verify all figures.
To start there are three kinds of SOHC VTEC that Honda has ever produced. First there is standard SOHC VTEC this was found on the 1996-2000 civic EX (D16Y8), and the 1992-1995 EX and SI (D16Z6). This works the same as DOHC VTEC (only on the intake side no SOHC motor has VTEC on the exhaust side). By using three cam profiles and three rocker arms per cylinder, View diagrams. The second kind of SOHC VTEC is called three stage VTEC It is only found in the UK or Japan on a D15B. This kind isn’t really important to the USDM market, but if you want to read more on it follow this link. http://www.leecao.com/honda/vtec/3stagevtec.html The third and final kind of SOHC VTEC is VTEC-E This is found on the 1996-2000 civic HX and the 2001-2003 HX and (sorry to say it EX, yes that’s right are EX is a VTEC-E) VTEC-E is different because it only has two rocker arms and two lobes on the intake side (not Three) The way it works is from 0-4500 rpm one valve opens all the way while the other one opens less then when VTEC hits a Timing piston, spring and a Synchronizing piston all slide over locking the two together making the both open and close on the hotter cam profile. Here are the Cam specs for the D17A2 (look at diagrams 4 and 5)
D17A2 (EX)
Intake Exhaust (Remember the bigger the number the more it opens)
PRI 38.604 mm 38.784 mm
SEC 32.848 mm
So from 0-4500 rpm it is like having the equivalent of two valves opening at 35.726 (because one Is opening all the way at 38.604mm and the other not as much at 32.848mm) (this is still hotter then a lx with a 35.299 mm (Intake) and a 37.281mm (exhaust) after VTEC hits both rocker arms ride the 38.604mm profile that much better then the LX. This is the exact same way the HX works only the HX has slightly different cam specs.
D17A6 (HX)
Intake Exhaust
PRI 38.427 mm 38.784 mm
SEC 32.197 mm
D17A1 (DX/LX)
Intake Exhaust
PRI 35.299 mm 37.281 mm
They both have VTEC-E; the VTEC-E is for economy. But you say what my EX gets worse gas mileage then a DX LX and a HX Why? Simple, it’s all in the ECU. Honda dose some tricky things with there stock tuning. The EX has more fuel dropped in when in VTEC (Stock) then the HX. Infact the HX runs quite lean. Also the DX LX have a worse cam profile all the time allowing less air in so there for it needs less fuel. Not only this but the DX/LX, HX, and the EX all have different ignition Maps. Honda is so tricky with there stock ECU tuning that because of tuning alone that is why the Integra GSR makes all its power at high rpm’s, why did they do that you may ask. Because too many consumers complained about torque steer at low rpms for the first year of its production.
Now on to older SOHC VTEC. Standard SOHC VTEC is the same type you will find in a DOHC car (only without the exhaust side) how it works is there are three cam lobes and three rocker arms on the intake side. First from 0-4800 the outside rocker arms open and close by the outside lobes. Then when VTEC hits two Synchronizing pins slide over and lock onto the Mid Rocker. The Mid rocker follows the VTEC cam lobe.

Here are the specs for the D16Y8 cam
D16Y8
Intake Exhaust
PRI 36.778 38.008
MID 38.274
SEC 37.065

So the Y8 head is better until VTEC hits on are cars then are heads have a slight advantage.
Also another side note VTEC-E dose not use lost motion assemblies like every other kind of VTEC ever.

Here are the specs on what it takes to activate VTEC

1 Your MAP (Manifold Absolute Pressure) sensor must read 0hg (aka 0 inches of vacuum). When it reads this it will send a 3volt signal to the ECU.

2. Your throttle has to be open 100% because your TPS sensor has to send a 4.5-volt signal to the ECU.

3. Your coolant temp has to be at running temp.

4. Vehicle speed has to be above 20mph.

5. You have to have 65-80 oil psi.

6. The engine must be running at a minimum of 4500 RPM

When all of this happens your ECU sends a 12-volt signal to your VTEC solenoid.

Also a common misbelieve is that the louder you VTEC is the better. Absolutely not! Last month I got to drive a 11.874 sec N/A H22 powered 93 civic hatch. This thing had kick *** VTEC wow. When it hit it was like a kick in the nuts. But there wasn’t a big noise change, but wow you really felt it especially to run an 11 sec at 5280 ft above sea level.

So this is it everything on SOHC VTEC. I did a lot of research (reading tech books) and a lot of talking to a lot of people. I know all the Specs here are absolutely correct because they all cam from Honda Tech books, I have included scanned copies so nobody can refute these claims. Now its Friday night so I’m going to wrap this up so I can go out, but I will add more this weekend.

FingerJ

iTrader: (1)

Now thats what im talking about this needs to be Stickyed since the last one was tanted by 4drcivic2k1. and the last one should be erased.

Good work Caorndorff.

bakuretsu

Looks like 4drcivic2k1 was correct about the second set of valves opening at 4500 and NOT at 2000, as caorndorff said initially. This makes sense, as there is no mechanism to change the valve timings independent of V-TEC itself (which comes on around 4500 or so).

After all of that bickering in the other thread, caorndorff was mistaken.

C Orndorff

iTrader: (16)

No he said that all the valves were all the way open all the time, not true.

C Orndorff

iTrader: (16)

This is what i was trying to say the whole time but 4drcivic2k1 would not listen.

Jrfish007

iTrader: (3)

I didn't know the 7thegn EX where based on the VTEC-E... That's to bad So then I could take an HX ECM, put in my car and get 50+ MPG. BUt there was VTEC lean on the 92-95 civics too (or actually 94-95), just a not in passing

Jrfish007

iTrader: (3)

Good explination of Vtec though!!!

Metallica454

iTrader: (1)

I get what you are saying caorndoff. I think 4dr2k1 just misread or misunderstood what you were saying about the valves. If I may:

You are saying 2 valves are opened from 0001rpm to 2000rpm, then at 2001rpm we get all 4 valves opened. Then, at 4500rpm we get the hotter cam profiles thanks to VTEC along with the 4 opened valves that were taken care of earlier. And 4dr2k1 is saying all 4 valves are opened ALL the time from 0001rpm to redline which is trun in the D16 not the D17.

C Orndorff

iTrader: (16)

Kinda. The exhaust valves never change on any SOHC. Also form 0-4500 we have one intake open at 38.604mm and another at 32.848mm after VTEC hits at 4500 both intake valves open at 38.604mm. 4drcivic2k1 was mixing this up with a D16Y8 that has both intake valves opening the same amount untill VTEC then when VTEC hits they open even more.
D17A2 = 2 rocker arms 2 lobes (intake) D16Y8 = 3 rocker arms 3 lobes (intake)
So if you want to get technical you could say one valve is in VTEC all the time (and it is because it rides the VTEC lobe all the time) but the other one opens less untill VTEC so you save gas.

mradam85

thanks for the info thats some good stuff!

4drcivic2k1

iTrader: (2)

I never said they both opened the same amount. I said they OPENED. You stated that 2 valves we're closed, and then also said, that the exhaust valves never change. So, if we have 2 valves closed, how would the engine run if both intake valves are closed since the exhausts never change?

Metallica,
The valves only change once. There is no mechanical way for it to change more than once.

nindoo

iTrader: (1)

So caorndorff its possible that the more aggresive cams don't kick in after 4.5k rpm all the time? When would you have oil pressure to low or too high, I mean what causes your oil pressure to change?

C Orndorff

iTrader: (16)

I'm not even going to go there again. You are just looking to argue, and I do not want to ruin this thread with bickering like the last one. and I said only one valve was affected because there is no VTEC on the exhaust, ok.

big_daddy_b_99

iTrader: (7)

well that was very informative like the last post and since there are pics of the pages that the info came from there should now be no question on its accuracy

4drcivic2k1

iTrader: (2)

But you did say: "Only 2 valves open until 2000 rpm."

es2

but doesn't a hx have no ac

Civic04

iTrader: (1)

so normal running conditions (pre vtech) both exhaust valves open all the way and 1 intake valve opens all the way and 1 intake valve opens part way. When vtech kicks in under the preset conditions both exhaust valves open the same as before (becase no vtech on the exhaust side) and both intake valves open (fully) in the hotter cam profile .


Yes? No?

4drcivic2k1

iTrader: (2)

Yes.

C Orndorff

iTrader: (16)

VTEC dose nothing to exhaust on a SOHC motor. and the intake part is correct.

Jrfish007

iTrader: (3)

Yeah they have no AC, no CD, no sun roof... basically a DX with a VTEC motor?

Jrfish007

iTrader: (3)

OKay so our newer (D17) motor has VTEC on the intake, but it simply uses to cam lobes instead on three like the D16's. Does the VTEC-E affect the exhuast then or not? IF not, how come they get such good gas milage? You can not possibly say they get 50+ MPG when I am getting around 32 with the same motor. I've played with plenty of ignition curves, fuel curves and such and you won't get much better than what the factory gives you (maybe 5 MPG better), but that was on a '94 D16. So there must be somehting much more than the ECU to get that kind of MPG.

Jrfish007

iTrader: (3)

Man, I hope this thread doesn't get into i-VTEC...

gearbox

iTrader: (95)

I'm getting 20mpg max now does that mean my vtec is broken

C Orndorff

iTrader: (16)

NO SOHC VTEC Effects exhuast, ever. I am not just saying they are the same motor i know they are, just read the tech book pages I listed. If you took a HX and put a EX ECU in you would have a EX (almost the HX has one valve that dosent open as much but very very close)

C Orndorff

iTrader: (16)

No your ECU will always follow the same fuel map (unless you are changing it with piggy back) thats why its bad to lower your VTEC without adding more fuel.
I get about 25mpg but thats because i run rc 550cc injectors with a buch of boost.

aznboysrfr

iTrader: (10)

gsr vtec crosses over at 4400 rpms.

gearbox

iTrader: (95)

Okay maybe you might know this. How exactly does our ecu work? I've heard things like if you reset it, all the fuel maps get erased and the manual just says do it for idle learn. I've reset it whenever adding or removing mods, and most of the time the idle is already fine. Is it true that the fuel maps have to be relearned, or are they a permanent part of the ecu. I'm also using a vafcII to add a little fuel under wide hi vtec maybe 1-2% correction due to it running lean in lower rpms.

C Orndorff

iTrader: (16)

No the ECU know the fuel and igniton maps permanently. Thats why swaping out ECU's within B motors is so popular. And if you put a D17A2 ECU on a D17A6 you would see some small gains. because the EX ECU is set with a better igniton and fuel map

4drcivic2k1

iTrader: (2)

I can tell you how that works if you like?

C Orndorff

iTrader: (16)

Here is how i-VTEC works. http://asia.vtec.net/article/ivtec/