How do the variances in the VTEC motor cause such drastic hp differences? I know as far as torque goes, its all displacement. I would like to compare the new Honda Accord engine : 2.4L DOHC VTEC engine making roughly 160 bhp with 150-160 torque. As opposed to a S2000 with a 2.0 DOHC VTEC making 240 and 150 torque. Granted the S2K has a more highly tuned motor, but what do they do with them to make so much difference? I just finished driving my brothers 98 Accord and it as decent powerband but nothing compared to my Jetta 1.8T. As some of you might know, the 1.8T found in VW/AUDI uses a 20V 1.8L DOHC engine with long stroke and somewhat short bore. The turbocharger is a K03 that starts full boost at around 1500 but falls really short around 5K. I have actually beaten my share of S2K (not braggin buy proud of it) I had somewhat cheated cause I have really good low end torque and my mods have given me approx. 40whp. My mods are follows: Upsolute Chip, Turbo-back custom 2.75 mandrel bent piping exhaust, AEM CAI, and a divertor valve. But then again, the scream of a VTEC engine at 9K is nothing compared to the grunting and snorting of my diesel like engine.

 

biggest reason is compression...the S2K is at 11.0:1 compression....if you were to lower that to 9.0:1 like the motor mike simon builds for our car....the motor only puts out 160 HP!

 

ditto

 

the k24 found in the accord is tuned for good low-end, mid-range torque and runs out of steam in the higher rpms. this is partly due to the large rod-stroke ratio. plus the c/r ratio is low. i believe the i-vtec system adjusts the cam timing and lift at the sametmie, and normal DOHC VTEC only adjusts lift.

the f20c in the s2k has 11:1 compression, excellent flowing head, more aggressive cams and pistons. the f20c also has a low rod-stroke ratio. plus, DOHC VTEC yields better high-end hp numbers than the I-VTEC system.

 

If the compression ratio for the S2k is 11.0:1 then then it shouldn't be a good canidate for turbocharging? I know that a lot of VTEC owners tend to supercharge their motors. But in the long run isn't turbocharging more tuner friendly and ultimately yield more power?

 

the f20c is pretty reliable with a supercharger/turbo at only 6-7 psi(lots of people here run with a supercharger with no probs), any higher you will need reinforced internals and lower compression pistons. if you're going for maximum hp, turbo is definately the way to go. you can boost much higher with a turbo.

 

If I understand your question, you're asking how a VTEC motor gets some much more HP than some of its lesser brothers? The answer is the valve timing change (what VTEC does) allows the motor to breath well at higher RPM. That extends the torque curve much higher in RPM than is normal. Still making okay torque at higher RPM means more HP.

Consider some of the racing engines out there. I've heard of 1.5 L motors (with a turbo) pushing 1,000 HP. The big deal is the RPM they spin to without losing torque (like > 10K RPM).

A fundamental truth about traditional cam-valve-drive engines is that cam can only be "optimum" for one exact RPM. They operate less effectively at ANY other RPM. By switching to another cam timing, VTEC engines now have two RPM's at which they are "optimum." The dream, soon to be reality, is a camless engine with continuously variable valve timing. More power and better mileage, coming soon to a BMW or Vette near you.

If that wasn't your question maybe you can rephrase it?

 

the higher compression makes the S2K not boost friendly.....look at any turbo car from the factory and you will notice that the compression is at 9:1 or lower......that is why the mike simon motor for the S2K at 9:1 compression can handle 30 PSI without any problems...

Our car likes some boost, but just 1 PSI too much, and bye bye F20C!

 

I heard this too. The new vette, the Z0 whavetever it will be called will have pneumotic valves like airplanes do now.

I guess I vtec is the closest thing to that right now.

 

The VW/Audi 1.8T engines run 9.5:1, 9.3:1, and 8.9:1 compression