RPM Question on Turbo after Test Driving one

[OffRoader]

I come from a background of driving trucks and SUV vehicles, and actually have never really continuously drove a sedan "car". Or hatchback, etc. I like to watch my RPMs and at-least on the ones I drove for a few years could keep them at 2,000 give or take a little unless entering the highway but even at 75-80 holding 2,000-2,300 was not a problem and it is a little mountainy here.






Back to the point real quick - test driving the V Turbo threw me for a loop - when slowly accelerating onto the 60 mph limit freeway the rpms jumped up pretty high 3,000-4,000 I believe. Never above 65ish and even while in the 40s still kept up pretty high for RPMs that I am used to.




I am an avid googler and read a bunch of good stuff for GREAT info but it still didn't completely answer my question. Using the search function for RPM on here doesn't really work haha, I tried with ish results.


1. Do all sedans/hatchbacks act that way with rev'n higher RPMs? Read that different vehicles have different 'bands?' on them or something, was a little messy on the articles. I assume the smaller engine accounts for the higher RPMs to get more juice out of it..or along the lines.




2. Did read that certain engines have sweet spots where they are tweaked to work the best, really the main question for the VT owners on here - what is the VT's sweet spot was for RPMs?




Digging through posts I saw that the turbo really kicks in at around 4,000 RPM. I guess I just don't know how to compare the VT being a Truck/SUV owner all these years. Felt weird to me having to rev the VT up way past normal for same horse power/acceleration. While the SUV might have a better engine the truck wasn't anything special and accelerated more than fine to highway speeds at a steady low RPM.




Note: Drove an Automatic (city traffic can suck here) and plan to get that when buying. Rest of the car blew me away though..nice little package

[cheferman65]

Remember you are comparing a 1.6L $ Cyl to the 6 Cyl., So all of your assumptions are correct.

[Velos510]

Agreed ^^^...I had a Mazda protege5 and RPMs would run high at speeds where in other cars would run low. Came to find out it was normal. A larger engine would normally run at lower rpms compared to a smaller one to reach the power but then again it just depends on the car.

[wbw]

The VT is a small motor with turbo. Don't try to compare it with trucks and SUVs.

[cbrmale]

The turbo is throttle-restricted for the first few thousand kilometres and the engine is also very tight, and what happened here was the automatic gearbox sensed the engine was labouring and down-changed a gear. Once it runs in it will pull stronger from lower revs and is less likely to do down-change to accelerate, although the sweetest part of the powerband is around 4,000. Don't be afraid to let the engine rev out to 3,000 or 4,000 as it's a small engine and the inertia of small, light pistons and small, light valves is much less than a large capacity engine, so it will pull high revs with no stress and very little wear.

Double the weight of a piston or valve and you increase the inertia (forces that cause wear) by a factor of 10, so you can pull high revs on a smaller engine with much less wear than a larger engine. The ultimate example of this is multi-cylinder sports motorcycles which are quite comfortable at 10,000+ rpm.

[OffRoader]

Wow, great info! Makes sense now - appreciate it

[Curmudgeon]

The VT is a small motor with turbo. Don't try to compare it with trucks and SUVs.

Or even motorcycles, some of which have engines with larger displacement (e.g. 1832cc) and greater horsepower than a NAV (e.g. 160HP).

[sn4cktime]

My little 250cc commuter bike doesn't even red line until 12k and hits the rev limiter at 16k.

I've been driving my VT for a few months now. I've always been a follower of the "break it in hard" policy to get everything in the engine scrubbed down while it still had all the factory additives in everything and to seat the rings under higher pressures. *disclaimer, this is how I treat MY vehicles and in no way am I endorsing it.

Turbo really comes to life around 4k for the automatics, and boosts more in sports mode (along with not jumping gears as much). My V seems quite happy pushing the needle WAY into the red once warmed up. Most nights when I drive home I have to go up a huge hill with a speed limit of 70Km/h. I usually pin it until I hit just under double that.


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[MTD]

Most small displacement motors typically rev much higher and make their HP and TQ higher. The VTs 1.6 makes its 201hp at 6000rpms, Hondas VTEC motors upwards of 9000rpms, many many motorcycle engines 15000rpms, etc.

A larger displacement truck/SUV engine revs much lower and makes its power lower in the rpms. There are the odd bigger car motors that love to rev though. The V6 in my Genesis or even a new Corvette or Mustang.

Dont be afraid to rev them.

[tidybowl]

Driving a small 4 cyl is much different then a big v8. Even powerful turbo 4's need to be revved to make power. My old Evo was gutless until about 3k rpm, then a huge burst of power. A lot of Hondas don't make power until after 4k. Just have to get used to it.


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[sn4cktime]

... A lot of Hondas don't make power until after 4k. Just have to get used to it.

I miss my 89' CRX si... It's gas pedal really only had two positions, off or floor panel..

[cheferman65]

Or even motorcycles, some of which have engines with larger displacement (e.g. 1832cc) and greater horsepower than a NAV (e.g. 160HP).

1340CC in my beastie and she puts out 198RWHP!!!

Talk about power to weight ratios.....

[sc.veloster]

1340CC in my beastie and she puts out 198RWHP!!!

Sounds like time for a motor swap

[TheBlackBass]

The fuel map changes at 4k, it goes from a 16:1 ratio down to a 10:1 around 5k If I remember correctly. So that boost you feel isn't the turbo spooling (turbo is spooled right before 2k) its just the engine running richer.

[cbrmale]

I have seen a dyno chart with the air-fuel ratio, although dyno is full load, full throttle and not indicative of normal driving. In any case the air-fuel ratio did start at 16:1 and by 5,000 it was 10:1 and getting richer, but the increase in mixture richness was progressive (a straight line). The reason for this richness should be obvious. Hyundai are using fuel to cool the internals of the motor at high revs and high load, which is a common practice with turbocharged engines, especially turbocharged competition engines. The Veloster puts out a lot of power for a 1.6 and it would need some cooling.

I don't have a boost gauge but it's clear the engine reaches boost low down in the rev range, or else it wouldn't pull so strongly from 1,500 to 2,000 rpm. I think around 4,000 is where everything feels good, and above 4,000 the engine starts to feel coarse and thrashy.

As far as I know we don't have 2-litre motorcycles here because most Australian riders (like most Australian drivers) are more interested in handling finesse than straight-line performance. My motorcycle is a 900cc air-cooled two-cylinder with twin overhead camshafts, four valves per cylinder and fuel injection. It is red-lined at 8,000 so it's docile, and it does it's best work around 4,000. Even so it is 450cc per cylinder, so it's proportionally bigger than the 1.6 four in a Veloster. It can pull 8,000 because it has a drop-forged steel crankshaft, where motor car crankshafts are cast iron and would break into a million pieces at those revs.

The idiom of Americans obsessed with acceleration and the rest of the world more interested in chassis dynamics is an interesting one to me. We have many Americans on this forum wanting more power for their turbos where we have clearly better steering and handling on our version, because that's how the car will be evaluated in Australia (and in Britain and Europe). I bought my turbo because it was one of the better steering and better handling cars I have ever driven, and that's what I concentrated on when I took it for a test drive.

[TheBlackBass]

Yea full boost can be reached at 1750, it usually spikes to around 20 then drops a bit from there. A rich mixture gives more power, think old american muscle cars. They make gobs of power but suck down gas. Hyundai kept 16:1 for fuel economy but makes it richer at higher rpms to reach full power. They are not using the fuel mixture to help cool the engine. This car is liquid cooled, not like an air cooled motorcycle which needs the help.

[cbrmale]

Yea full boost can be reached at 1750, it usually spikes to around 20 then drops a bit from there. A rich mixture gives more power, think old american muscle cars. They make gobs of power but suck down gas. Hyundai kept 16:1 for fuel economy but makes it richer at higher rpms to reach full power. They are not using the fuel mixture to help cool the engine. This car is liquid cooled, not like an air cooled motorcycle which needs the help.

Direct fuel injection is all about internal engine cooling, and remember that exhaust valves get up to 1200 degrees (even though the VT has sodium-filled exhaust valves). The one, only and sole advantage of direct fuel injection is the fuel is not pre-heated by inlet air, so it goes in cold and cools valves, pistons and other engine hot spots. Normally aspirated direct fuel injection engines run around 12:1 compression, because internal engine cooling allows high compression without pre-ignition. In competition with turbocharged racing cars, also liquid cooled, it's quite common to see a haze of black smoke from the exhausts under power for the same reason. To cool the internals of the motor.

Crude, old American engines with inverted bathtup combustion chambers are prone to engine hot-spots, which is why they also need rich mixtures. Again it's for cooling, and the alternative would be to lower compression to reduce pre-ignition, but lower compression costs power. So rich mixtures are all about keeping the internals of the engine cool, enabling higher compression ratios, more spark advance and in the case of turbocharged engines, to allow for more boost.

My air-cooled motorcycle is partly oil-cooled. It holds 5 litres of oil and has two oil pumps: one to pressure-feed the engine and the second pump to flow oil through an oversized oil cooler which is about half the size of a liquid cooled motorcycle's radiator. It actually runs very lean in stock form: 17:1 right through the powerband. This is to pass Euro III emission control standards in conjuction with catalytic converters in the exhaust headers. My Bonneville has optional high-flow exhaust silencers and a re-mapped ecu which brings the mixture to 15:1, which is close to optimal for power. Operating oil temperature is 80 degrees in colder weather and up to 100 degrees on a hot day, say mid thirties ambient, so engine temperates are not terribly high. The problem is the other end of the scale and it's necessary to pamper it until the oil warms up, which takes a fair while. The oil cooler is inline all the time or else the oil level in the sump would be too high.

Air-cooled Harley Davidsons are prone to overheating but this is because the front cylinder blocks air flow to the rear cylinder. It's a basic design flaw. A parallel twin ís better suited to air-cooling.

[TheBlackBass]

Touche, I stand corrected on the cooling aspect. However I do KNOW a richer mixture gives more power and since the boost isn't increasing at 4K according to my Torque app, I can only assume it's the change in AF ratio giving the extra pull. So regardless of the exact reason, a richer mixture gives more power. What I would love to know for certain is how much cooler does the extra fuel make things? I had always thought the rich mixture was to ensure the burning of as much air as possible, like an afterburner on a jet which just sprays more fuel into the exhaust to burn any left over oxygen. But I had never considered the cooling effect. So perhaps the reason a rich mixture gives more power is 2-fold, cooler temperatures allowing more air and compression, and more fuel to burn as much air as possible. Sound logical cbrmale? You seem to know your ****.

[cbrmale]

If there is a boost of power at 4,000 it may be due to the variable camshaft system, but I don't know much about those because I only built engines for racing and we had one camshaft profile for maximum power! With a conventional engine a step in power is usually associated with valve timing (lift and overlap) reaching optimal performance.