Nissan and VW engines vs. Honda/Acura high rev engines

[curtis73]

I don't think anyone has truly answered the question. Or at least what I though he was fishing for...

Wayoutcat... Since engines are basically air pumps, by altering the qualities of the ingested air we can alter the power output qualities. We do that by changing intake, head, cam, exhaust, and other physical factors. The two main considerations are intake velocity, and intake mass. How much air can you ingest, and how fast its flowing in. Generally, faster is better but to get it faster we have to either reduce the size of the intake path (which reduces the mass we can ingest) or rev the engine higher. Since (for the most part) engines' physical parameters are set and can't be changed without a die grinder, the balance that happens between velocity and mass is a function of RPMs. There is an RPM point in each engine where this velocity is maximized. Anything below that RPM is moving the air slower. Anything above that RPM and it becomes a restriction.

And as a sidenote; VTEC or other variable valve timing as these folks have already said, is a means of keeping the valves open longer at higher RPMs. Once you pass that critical max velocity, you can't speed up the air anymore. The idea is to hold the valve open longer so that it can get more air mass that way. In this way you can stretch your effective power band with very little trade-off. Its not overly effective since cams, heads, intakes, and everything needs to be tuned together. The VTEC dances around on either side of optimum tune in an attempt to stretch it and it works to a degree.

To answer your question the VW engine most likely has smaller ports in the head and smaller intake runners. This lets it peak its velocity (and therefore power) lower in the RPM range. Its trade off is less hp up high in the revs. The Honda probably has larger ports so it peaks velocity (and its power) at a higher RPM. Its trade off is less low end power. You have to rev it to get the power.

Each one is different, not better. I personally prefer the low end power in my life because I have big heavy cars. I could easily have built a 700-hp V8 for my big heavy station wagon, but chances are I would have needed large air passages to do it. Not a wise choice in a 5000-lb car to have to rev it to get it to move. I choose the power right off the line and instead I only have a 400-hp V8.

Where things really get fun is with today's computer modelling, designers can test head and intake flow qualities long before there is a head even built. The advancements happen when ever you can increase mass flow without increasing the size of the ports. Its a win-win situation because what happens is you get more air without reducing velocity. That serves to spread out the power over a wider RPM range and that's always a good thing on the street.

[sunfire_starter]

Originally Posted by duplox

wait for it...



wait for it...






Hey! There it is!
He probably told you it was 800hp, and its more like 300-320hp. Nothin to sneeze at... but 800hp is more than a lot. He would have to be pushin well over 30psi and revvin to 10k+ to get that much out of a 4. And if he was, he sure as hell wouldn't let someone whos driving experience that consists of a 150hp sunfire drive it.

You might be right, I wouldn't know. All I have is my cousin's word since he is the mechanic that worked on it. It is a drag car that this guy brought in to get worked on for like the umteenth time there so he was cool enough to let my cousin and I drive it after it got worked on. Maybe my cousin was lieing about it being 800 hp because that does seem like alot. I didn't have a dyno graph or anything like that in front of me to say it was 800 hp all I knew is that sucker could move.

[duplox]

I don't doubt it could move. Sorry I came off as a big dick in that post, I wasn't in a very good mood at the time. I wouldn't be suprised if the number of 800hp civics in the world was under 20.

[Steel]

Im wondering if the VW/Nissan engines are also utilizing a longer stroke and smaller bore ratio to produce more low-mid torque at the sacrifice of high end powahhhh... and revs. I haven't personally checked the redlines of these engines.

I don't personally care for pistons as it is, but to add an example of sorts to curtis's post would be the 91 (?) Mazda LeMans car; the 4 rotor R26B engine, with fully variable length intake runners. I dont remember the exact dimensions, but motors would vary the length of the velocity tubes quite a bit depending on the RPM and load to strike a nice balance between maximum efficiency and power.

[curtis73]

When all of these technologies come together it will be exciting.

Variable length/diameter runners
variable duration/lift cams
variable compression
variable exhaust length/diameters

At this point we've scratched the surface of some of these technologies, but they aren't a reliable way yet. Some day....

[Steel]

I don't know how feasible variable compression (other than varied forced induction) would be, but i think within the next 10 years or so, we'll be seeing solenoid activated valves. Infinite lift and duration variables. That will be pretty sweet if you think aobut it. Every car will have the tamest and hottest cam in there at the same time. Althouhg it does kind of take the fun out of listening to the idle of a big ole V8 with a stupid lopey cam. I may not like pistons, but i'd be lying if i said i didnt like the "wub-wub wub-wub-wub" of a 426 barely turning over.

[curtis73]

Actually, either Saab or Audi (I forget) had a variable compression engine on the road. The crank case and block were separate entities and the crank case could pull away on a hinge from the block. The displacement remained the same, of course, but the comustion space could be increased that way.

It was tuned much like an ignition advance; more compression at light loads and accelerating, and less compression under heavy load or high RPMs. They sucked. It didn't really do much for the engine since compression isn't really the holy grail that everyone has been told it is. It boosted hp by about 2 and offered terrible reliability.

Now, if it could have been coordinated with the other variables, then you have an infinitely matched set. You would have the large cam, high compression, short runner monster when you needed it, and the mild cam, low compression, long runner grunt mill when necessary.

[WayOutCat]

thanks Curtis!

[bjdm151]

Thanks Schista,

Sometimes a post needs an ass. I often see it as a resposnsability.

Besides simply because there are a billion kids out there driving civics doesn't meen that there are a greater number of parts available or the potential for that platform to make power is any greater. And where an engine makes its power, in the case of these engines is not because of the size, I believe all three make generally the same range of engine sizes, except for VW wich currently has big w8 and i believe w16(bugatti) engines in production. And yes Honda might have been in F1 for a while, but F1 is not the only form of racing where prototypes are involved. How long did Audi dominate Le Mans? I also remember nissan had its hat in the ring of the prototype world for a while. And what about production racing.

Open your mind to something other than a Honda.

[SaabJohan]

Originally Posted by curtis73

Actually, either Saab or Audi (I forget) had a variable compression engine on the road. The crank case and block were separate entities and the crank case could pull away on a hinge from the block. The displacement remained the same, of course, but the comustion space could be increased that way.

It was tuned much like an ignition advance; more compression at light loads and accelerating, and less compression under heavy load or high RPMs. They sucked. It didn't really do much for the engine since compression isn't really the holy grail that everyone has been told it is. It boosted hp by about 2 and offered terrible reliability.

Now, if it could have been coordinated with the other variables, then you have an infinitely matched set. You would have the large cam, high compression, short runner monster when you needed it, and the mild cam, low compression, long runner grunt mill when necessary.

The Saab Variable Compression engine, SVC is a 1.6 litre 5 cylinder engine developing about 225 hp. It uses a Lysholm compressor and max boost was around 2 bar (2.8 bar absolute if I remember correctly).

The engine decreased fuel consumption by around 30% (this is more than other concepts) compared to a normal engine with the same power output.

With variable compression it allows a small highly boosted engine for high power outputs, but a small NA high CR engine for low loads (as when driving at constant speed). This allows basicly two engines in one. Otherwise a small highly boosted engine must made low CR, and a high CR NA engine must be made low power. Generally the engine is designed around the well known downsizing concept, giving it a decreased fuel consumption.

The engine concept wasn't completly developed due to economic reasons. As I understood it one of the problems was to make the change of CR fast and smooth. For example, when the driver give full thottle the engine must fast angle the monohead against the crankcase which holds the crankshaft and turn on the compressor. The compressor was used instead of a turbocharger since it could easily be controlled, still the engine was very complicated to control and demanded a very advanced control system. The engine was actually invented in the early eighties, but back then there wasn't computer power enough to make one (at least if we want a microcomputer).

http://www.saab.com/main/GLOBAL/en/vepsilon/
http://www.saabnet.com/tsn/press/000318.html
http://www.memagazine.org/backissues...otto/otto.html

[curtis73]

Excellent post, SaabJohann. The one I had seen was not forced induction, so it didn't take much advantage of it. That was at one of the auto shows way back when. It was one of those cutaway engines that was all chrome plated and powdercoated. Looked impressive, but the ones I heard about shortly after that didn't do much on the street.

Thanks for clarifying.