max RPM while compression braking - Toyota Yaris Forums

Idahotom · 10-26-2010, 12:17 PM

I live on a mountain with a long 12% downgrade. Coming down with my 5 sp. '08 HB, I of course am in DFCO the entire way, that's the good part.

I am unsure what the redline is of the Yaris engine, keeping in mind that running at redline while going downhill it would seem be easier on the engine then at the same RPM while pulling hard. I hate to ride my brakes, or shift down to avoid riding the brakes and then be going 25 mph (people drive the hill at 40 to 55).

What I'd really like is a compression brake like I have on my truck, but that ain't gonna happen! So... any thoughts on the max permissable rpm while in downhill/FDCO mode? I'll brake if I have to, brakes are cheaper then a new engine.
Tom

RedRide · 10-26-2010, 01:07 PM

Actually, the strain on the valve train is the same either way. Also the stain on the rest of the engine is simular.
So, the same RPM concens apply.

Most race car drivers will tell you they prefere to use brakes for braking as engine braking puts an unnessary strain on the engine and brakes are easier to replace.

As always, when driving, a bit of common sense goes a long ways and circimstances certainly comes into play here.

Idahotom · 10-26-2010, 02:15 PM

I guess I'm thinking of manifold pressure maybe, or something like that... I can't believe the engine is strained equealy at high rpm's when unloaded (going downhill) as compared to pulling hard. I know in my Cat diesel powered boom truck, when I use the engine/exhaust brake (going down the same hill), my local CAT dealer service manager said don't go over 300 rpm above the governed RPM. RPM is only one indicator of the engine work being performed, I mean I've never had a engine overheat while going down a hill at high RPM and I have going up!

As I drive this hill every day, and hope to drive it the "right" way if possible, (put it in 2 nd. or 3 rd, and let it accelerate until it reachs its max speed with my foot off the throttle AND off the brake, AND that speed is about right for the road AND I'm not over revving the engine.) I'll make a note next time via the Scan Gauge on a few parameters when doing so. Is 11,000 RPM too high?? JUST KIDDING!! If I have to hit the brakes a few times to keep the revs within a RPM limit I'll do so, but we long time residents of this area take a bit of twisted pride in not doing so. You can always tell a non local, as their brake lights will be on the whole way down, and you can smell cooked brakes, while the locals are flying down the mountain brake lights unlit (and brakes cool).

RedRide · 10-26-2010, 04:07 PM

Ther is no added or reduced strain on the valves because they are simply cam driven either way and it's all the same to them at any given RPM.

HTM Yaris · 10-26-2010, 06:14 PM

For everyday driving on relatively flat ( < 5 % ) using brakes is cheaper . For everyday driving in > 5 % using the engine is cheaper and safer .

Idahotom , in second gear the rev limiter will engage at 62 mph and 93 mph in third . Second gear will give more than enough power to get you up the hill at the speed you stated without "knocking" or "pinging" especially if you use premium fuel ( 92 or 93 octane ) . Personally I would not put car into third gear until I reach at least 50 mph going up a 12 % grade . Going down third gear is perfect .

Oh 1 other thing , for your particular application , I would highly recommend Amsoil , if you are not already using it

My Yaris ( Coryn ) is no stranger to the Mountains

http://www.youtube.com/watch?v=OBT2e9E9yFA

10-26-2010, 12:17 PM	#1
Idahotom Drives: 2008 5 sp. LB Join Date: Oct 2010 Location: Idahoi Posts: 268	max RPM while compression braking I live on a mountain with a long 12% downgrade. Coming down with my 5 sp. '08 HB, I of course am in DFCO the entire way, that's the good part. I am unsure what the redline is of the Yaris engine, keeping in mind that running at redline while going downhill it would seem be easier on the engine then at the same RPM while pulling hard. I hate to ride my brakes, or shift down to avoid riding the brakes and then be going 25 mph (people drive the hill at 40 to 55). What I'd really like is a compression brake like I have on my truck, but that ain't gonna happen! So... any thoughts on the max permissable rpm while in downhill/FDCO mode? I'll brake if I have to, brakes are cheaper then a new engine. Tom Last edited by Idahotom; 10-26-2010 at 06:11 PM.

10-26-2010, 06:14 PM	#5
HTM Yaris resident senior View User's Garage Drives: 07 Yaris Join Date: Jan 2007 Location: south Carolina Posts: 814	For everyday driving on relatively flat ( < 5 % ) using brakes is cheaper . For everyday driving in > 5 % using the engine is cheaper and safer . Idahotom , in second gear the rev limiter will engage at 62 mph and 93 mph in third . Second gear will give more than enough power to get you up the hill at the speed you stated without "knocking" or "pinging" especially if you use premium fuel ( 92 or 93 octane ) . Personally I would not put car into third gear until I reach at least 50 mph going up a 12 % grade . Going down third gear is perfect . Oh 1 other thing , for your particular application , I would highly recommend Amsoil , if you are not already using it My Yaris ( Coryn ) is no stranger to the Mountains http://www.youtube.com/watch?v=OBT2e9E9yFA __________________

Similar Threads
Thread	Thread Starter	Forum	Replies	Last Post
Turbocharged Dyno Result	cdydjded	Forced Induction Forum	24	08-23-2010 11:54 PM
yaris and yaris S	Y@R15	General Yaris / Vitz Discussion	54	09-14-2009 01:40 PM
Source code for Yaris Tachometer	metalshark	DIY / Maintenance / Service	27	04-06-2009 01:41 AM

10-26-2010, 01:07 PM	#2
RedRide Drives: '09 Yaris carmine red 2d HB Join Date: Jun 2009 Location: Middletown, NY Posts: 1,502	Actually, the strain on the valve train is the same either way. Also the stain on the rest of the engine is simular. So, the same RPM concens apply. Most race car drivers will tell you they prefere to use brakes for braking as engine braking puts an unnessary strain on the engine and brakes are easier to replace. As always, when driving, a bit of common sense goes a long ways and circimstances certainly comes into play here.

10-26-2010, 02:15 PM	#3
Idahotom Drives: 2008 5 sp. LB Join Date: Oct 2010 Location: Idahoi Posts: 268	I guess I'm thinking of manifold pressure maybe, or something like that... I can't believe the engine is strained equealy at high rpm's when unloaded (going downhill) as compared to pulling hard. I know in my Cat diesel powered boom truck, when I use the engine/exhaust brake (going down the same hill), my local CAT dealer service manager said don't go over 300 rpm above the governed RPM. RPM is only one indicator of the engine work being performed, I mean I've never had a engine overheat while going down a hill at high RPM and I have going up! As I drive this hill every day, and hope to drive it the "right" way if possible, (put it in 2 nd. or 3 rd, and let it accelerate until it reachs its max speed with my foot off the throttle AND off the brake, AND that speed is about right for the road AND I'm not over revving the engine.) I'll make a note next time via the Scan Gauge on a few parameters when doing so. Is 11,000 RPM too high?? JUST KIDDING!! If I have to hit the brakes a few times to keep the revs within a RPM limit I'll do so, but we long time residents of this area take a bit of twisted pride in not doing so. You can always tell a non local, as their brake lights will be on the whole way down, and you can smell cooked brakes, while the locals are flying down the mountain brake lights unlit (and brakes cool).

10-26-2010, 04:07 PM	#4
RedRide Drives: '09 Yaris carmine red 2d HB Join Date: Jun 2009 Location: Middletown, NY Posts: 1,502	Ther is no added or reduced strain on the valves because they are simply cam driven either way and it's all the same to them at any given RPM.