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 ass 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.
Originally Posted by drmcivicsi
yno Results: Our AUTO transmission 2001 Civic EX made 90 WHP & 84 WTQ prior to turbo, and after the addition of our turbo kit made 146.7 WHP & 121.9 FT/LBS of WTQ @ circa 8 PSI w/ a T3 Super 60 turbo, on 93 Octane. With a Manual we should put down 176 WHP and 140WTQ (no additives or sprays & running a fully functional catalytic converter on the down pipe) on a 76 degree day in Buffalo, NY. That is a 63% power increase, and a 45% torque increase at the wheels on a mere 8 PSI on a stock motor, automatic transmission vehicle.
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