Engine braking / compression braking difference between 4 and 6 cylinder engines?

[mnforester]

Quick question - is there a difference in compression (engine) braking between 4 and 6 cylinder engines with automatic transmission?

I rented a 4 cyclinder Sahara in Hawaii and tried using compression braking coming down from a volcano and I had to ride the brake in 2H, 4H, and even 4L (in manual first gear). Wondering if my 6 cylinder will do better on steep grades.

Thoughts?

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[Dan M.]

I have a 3.6 and my wife has a small displacement engine in her Chevy equinox. I believe larger engines provide more resistance when engine braking as larger engines have more mass and it takes more energy to move the internals. Probably explaining this wrong, hope you know what I mean.

 

[No IFS]

I can tell you that the compression braking on my 3.6’s incredible. The auto transmission in combination with the compression braking it’s the best driving vehicle I’ve ever owned.

 

[AlgUSF]

I can tell you that the compression braking on my 3.6’s incredible. The auto transmission in combination with the compression braking it’s the best driving vehicle I’ve ever owned.

Try it with the 6MT, it seems my manual transmission vehicles keep rotors forever.

 

[Some Random Guy]

Does the I4 have a lower cylinder compression? If so would that reduce the amount of braking it can apply in addition to the lower displacement? I thought turbo engines usually had lower compression so the turbo can ram more air in there, but I’m not an engine person.

 

[No IFS]

Try it with the 6MT, it seems my manual transmission vehicles keep rotors forever.

No thanks, Gave up on manual transmissions along with drum brakes and carburetors. Love my eight speed auto.

 

[AlgUSF]

Does the I4 have a lower cylinder compression? If so would that reduce the amount of braking it can apply in addition to the lower displacement? I thought turbo engines usually had lower compression so the turbo can ram more air in there, but I’m not an engine person.

More engine braking -- shift down
Less engine braking -- shift up
Leave it in D and you get little drag from the engine because it'll leave the transmission in overdrive.

When I take my Tundra to the mountains, I'm always in 'S' and dropping a few gears on the downhills. Our odyssey doesn't have that option, so I just hit the 'D3' button and use the brakes more often. When I take our manual transmissions, I wind them out in low gears. My Jeep could use a 'Jake Brake'.

 

[mnforester]

I can tell you that the compression braking on my 3.6’s incredible. The auto transmission in combination with the compression braking it’s the best driving vehicle I’ve ever owned.

Great to hear. Do you have a Sport, Willys, or Rubicon?

 

[No IFS]

Great to hear. Do you have a Sport, Willys, or Rubicon?

2019 Rubicon 2 door

 

[mnforester]

Thanks all for the thoughts. Living in flat Minneapolis means that I'll have to travel up to the North Shore of Lake Superior to find some decent long grades to see if my auto V6 compression brakes better than the 4 banger. It can't do worse because that 4 cylinder was pretty terrible.

 

[Petey]

Does the I4 have a lower cylinder compression? If so would that reduce the amount of braking it can apply in addition to the lower displacement? I thought turbo engines usually had lower compression so the turbo can ram more air in there, but I’m not an engine person.

4T has lower compression apart from that 3.6 has more cylinders a difference should be felt.. an engine person would be a good character name on the rick and morty cartoon.

 

[Upnarms]

No experience with the 2.0 other than when I had a loaner. But I can say in 4L in my rubi 3.6, if i place the auto in manual mode, 1st gear brakes big time... Was a crawl down shafer trail. If i left in auto mode it would end up in 8th quickly with not much engine brake.

 

[J0E]

Quick question - is there a difference in compression (engine) braking between 4 and 6 cylinder engines with automatic transmission?

The 6 has 2 more cylinders and higher compression so I'd predict more compression breaking potential, over 50% more. Never tested my assertion.

I rented a 4 cyclinder Sahara in Hawaii and tried using compression braking coming down from a volcano and I had to ride the brake in 2H, 4H, and even 4L (in manual first gear). Wondering if my 6 cylinder will do better on steep grades.

Where were you in 4H? what was your RPM and gear?

I come off the volcano in my JLR 2.0T with auto, M shifting, 37's, & stock gears with minimal brake input.

I had to ride the brake in 2H, 4H, and even 4L (in manual first gear). Wondering if my 6 cylinder will do better on steep grades.

Where were you in 4L? what was your RPM in M1 that you needed to ride the brake?

With the Ruby 4.10 diffs, 4:1 xfer case & stock 33's, M1 in 4L rarely required brakes (dropping off ledges obviously does). But with same gearing on my 37's, I need breaking more often.
I much prefer the 2.0T, extra bonus at altitude. I burn half the fuel the JK & JL 3.6s burn on the trail, but much of that is my aggressive use of MSS (Manual SS).

 

[mnforester]

The 6 has 2 more cylinders and higher compression so I'd predict more compression breaking potential, over 50% more. Never tested my assertion.



Where were you in 4H? what was your RPM and gear?

I come off the volcano in my JLR 2.0T with auto, M shifting, 37's, & stock gears with minimal brake input.



Where were you in 4L? what was your RPM in M1 that you needed to ride the brake?

With the Ruby 4.10 diffs, 4:1 xfer case & stock 33's, M1 in 4L rarely required brakes (dropping off ledges obviously does). But with same gearing on my 37's, I need breaking more often.
I much prefer the 2.0T, extra bonus at altitude. I burn half the fuel the JK & JL 3.6s burn on the trail, but much of that is my aggressive use of MSS (Manual SS).

Hey thanks for the comments. Yes, tried 2H, 4H, and then 4L using manual gears. None could keep me from rolling faster and faster and RPMs went too high for my liking. I don't recall what the RPMs were - but clearly going too high.

I also believe that your Rubicon gearing vs my Sport S gearing will also make a difference. I hope my Wrangler can engine brake enough to make trail running in Rockies enjoyable. I'll try to find some steep slopes here in Minnesota to test out capabilities.

 

[blnewt]

Hey thanks for the comments. Yes, tried 2H, 4H, and then 4L using manual gears. None could keep me from rolling faster and faster and RPMs went too high for my liking. I don't recall what the RPMs were - but clearly going too high.

I also believe that your Rubicon gearing vs my Sport S gearing will also make a difference. I hope my Wrangler can engine brake enough to make trail running in Rockies enjoyable. I'll try to find some steep slopes here in Minnesota to test out capabilities.

You can also use hill descent in 4Lo and not even worry about brakes (or I should say "applying" your brakes, let the computer do it for you

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