Go Back   EcoModder Forum > EcoModding > EcoModding Central
Register Now
 Register Now
 

Reply  Post New Thread
 
Submit Tools LinkBack Thread Tools
Old 11-06-2012, 02:32 PM   #1 (permalink)
EcoModding Lurker
 
Join Date: Mar 2012
Location: usa
Posts: 22
Thanks: 0
Thanked 0 Times in 0 Posts
Honda, Higher compression = better mpg?

Hey guys I drive a Honda Civic with a D16z6 sohc vtec engine with ~9.2:1 compression ratio. I have read a few times in a few differant places that higher compression ratio can lead to better mpg, as long as you still drive "correctly".

I am feeling as thought my stock engine needs a rebuild to remain efficient and was wondering about the compression=mpg saying that Ive heard. Would a rebuilt 10.5:1 D16 allow for better mpg than a 9.2:1 D16 if correct driving methods were retained? Also, would a slightly larger cam help as well? Being vtec, the engine runs on "small" cam lobes for cruising, but has "larger" cam lobes for wot/passing situations.

I am looking to rebuild my engine anyways and looking for slightly better mpg, but also slightly more passing power so,
Will slightly higher compression help with mpg?
Will a slightly larger cam help aswell?
Anything else I can do while rebuilding to help with mpg?

  Reply With Quote
Alt Today
Popular topics

Other popular topics in this forum...

   
Old 11-06-2012, 04:28 PM   #2 (permalink)
Burn lean and prosper\\//
 
Join Date: Jul 2012
Location: scranton pa
Posts: 576

VLX - '93 Honda Civic VLX
Team Honda
90 day: 51.1 mpg (US)
Thanks: 55
Thanked 65 Times in 54 Posts
i dont think the cam will help with mileage. ive heard the A6 cam is the best (smallest?) for mileage.

as for the compression ive heard the same as you have, that higher compression will help. only real way to tell with your individual vehicle is to do it and see what happens. do as much recording of your current mileage as you can and either do the head gasket or rebuild the entire thing. you can get all different thickness head gaskets and you can plug the numbers into a d series compression calculator. i did a d15b7 with a z6 head gasket and shaved the head and came up with about 10:1 compression. i couldnt do a comparison because i got the car with a bad gasket. but i averaged 42-43 normal driving and highest tank i ever got was 50 mpg while EOC. i was using regular fuel too. i was happy with it. but now im doing a d15z1 swap
  Reply With Quote
Old 11-07-2012, 01:35 AM   #3 (permalink)
It's all about Diesel
 
cRiPpLe_rOoStEr's Avatar
 
Join Date: Oct 2012
Location: Porto Alegre, Rio Grande do Sul, Brazil
Posts: 12,548
Thanks: 0
Thanked 1,622 Times in 1,447 Posts
As long as you don't use the cheapest, lower-octane fuel which would lead it to knocking, raising the compression helps the MPG.
  Reply With Quote
Old 11-07-2012, 01:28 PM   #4 (permalink)
Master EcoModder
 
Join Date: May 2012
Location: USA
Posts: 2,643
Thanks: 1,502
Thanked 279 Times in 229 Posts
Depending on how you drive, disabling or avoid getting the vtec to kick in would be a start.

The newer Insight uses like a 11 to 1 compression with its fancy 2 plug per cylinder spark plug setup. It doesnt have the torque Id expect with such a high cr, all the power is around 5 grand unless you got the IMA system enabled and a full charge.
  Reply With Quote
Old 11-07-2012, 02:47 PM   #5 (permalink)
Administrator
 
Daox's Avatar
 
Join Date: Dec 2007
Location: Germantown, WI
Posts: 11,203

CM400E - '81 Honda CM400E
90 day: 51.49 mpg (US)

Daox's Grey Prius - '04 Toyota Prius
Team Toyota
90 day: 49.53 mpg (US)

Daox's Insight - '00 Honda Insight
90 day: 64.33 mpg (US)

Swarthy - '14 Mitsubishi Mirage DE
Mitsubishi
90 day: 56.69 mpg (US)

Daox's Volt - '13 Chevrolet Volt
Thanks: 2,501
Thanked 2,585 Times in 1,553 Posts
Increasing compression might increase fuel economy. I say might because its not a simple yes/no answer. In an ideal engine with no other changes, increasing compression will increase power output and efficiency. However, there is no such thing as an ideal engine in the real world. Increasing compression has effects on preigintion and just ignition timing in general. Usually, with high compression you need to retard timing at higher engine loads so you can avoid knock/preigintion. This reduces efficiency. IMO Honda makes great engines and I'd be a bit surprised if you could eek out a noticable gain.

A shorter duration cam would give you more lower rpm power while sacrificing high rpm power. Your vtec helps negate this though. This also will return better mileage, and this can be a sizable gain. The Metro guys with XFI cams see a fairly decent gain.

IMO leave the engine alone. Do a compression test or leak down to see if you really need a rebuild. "Feeling" you need to rebuild an engine is just not possible. There are tests you can and should do to be sure.
__________________
Current project: A better alternator delete
  Reply With Quote
Old 11-07-2012, 07:41 PM   #6 (permalink)
Corporate imperialist
 
oil pan 4's Avatar
 
Join Date: Jul 2011
Location: NewMexico (USA)
Posts: 11,175

Sub - '84 Chevy Diesel Suburban C10
SUV
90 day: 19.5 mpg (US)

camaro - '85 Chevy Camaro Z28

Riot - '03 Kia Rio POS
Team Hyundai
90 day: 30.21 mpg (US)

Bug - '01 VW Beetle GLSturbo
90 day: 26.43 mpg (US)

Sub2500 - '86 GMC Suburban C2500
90 day: 11.95 mpg (US)

Snow flake - '11 Nissan Leaf SL
SUV
90 day: 141.63 mpg (US)
Thanks: 269
Thanked 3,522 Times in 2,796 Posts
Increased compression ratio - EcoModder
__________________
1984 chevy suburban, custom made 6.5L diesel turbocharged with a Garrett T76 and Holset HE351VE, 22:1 compression 13psi of intercooled boost.
1989 firebird mostly stock. Aside from the 6-speed manual trans, corvette gen 5 front brakes, 1LE drive shaft, 4th Gen disc brake fbody rear end.
2011 leaf SL, white, portable 240v CHAdeMO, trailer hitch, new batt as of 2014.
  Reply With Quote
Old 11-07-2012, 07:52 PM   #7 (permalink)
Master EcoModder
 
Join Date: Jan 2012
Location: United States
Posts: 1,756

spyder2 - '00 Toyota MR2 Spyder
Thanks: 104
Thanked 407 Times in 312 Posts
Higher compression ratio is more complicated than it seems. First of all in the ideal thermodynamic cycle one assumes constant heat ratio, but the more you compress the intake air the hotter it gets and the more the heat ratio drops. This is why in theory it's useless to increase compression ratio on spark ignition engines past a certain point; the temperatures get too high and the heat ratio drops.

Now for the practical side: You have to remember that higher pressures increase friction (particularly, at the rings). Additionally, reducing combustion chamber volume can cause a decrease in burn efficiency, and the higher burn temperatures result in greater rejection of heat to the cylinder walls and piston.

On the other hand, higher compression ratio given the same piston/rod geometry means more time is spent at lower chamber volume and thus higher pressures and so more of the charge burns at higher pressure. This effectively makes the exhaust valve act as if it were opening later, since more work is extracted on the expansion stroke. This effect gets more and more precious as the revs climb, because you have less and less time for the charge to burn. The "better solution" is to just increase the expansion ratio a la Atkinson cycle but this obviously decreases specific power, and you lose mechanical efficiency as a result.

Empirical data suggests that most of the time the benefits outweigh the drawbacks, until you get to the 13-14 :1 area, where careful attention has to be paid to combustion chamber shape, interference with in cylinder flow, etc. or else you can actually lose power/efficiency.

Last edited by serialk11r; 11-07-2012 at 07:58 PM..
  Reply With Quote
Old 11-08-2012, 05:16 AM   #8 (permalink)
Master EcoModder
 
euromodder's Avatar
 
Join Date: Jul 2010
Location: Belgium
Posts: 4,683

The SCUD - '15 Fiat Scudo L2
Thanks: 178
Thanked 652 Times in 516 Posts
Mazda is increasing the compression in their petrol Sky-Active engines.

And reducing it in the Diesel Sky-Active engines
__________________
Strayed to the Dark Diesel Side

  Reply With Quote
Old 11-08-2012, 06:37 AM   #9 (permalink)
It's all about Diesel
 
cRiPpLe_rOoStEr's Avatar
 
Join Date: Oct 2012
Location: Porto Alegre, Rio Grande do Sul, Brazil
Posts: 12,548
Thanks: 0
Thanked 1,622 Times in 1,447 Posts
Quote:
Originally Posted by euromodder View Post
Mazda is increasing the compression in their petrol Sky-Active engines.

And reducing it in the Diesel Sky-Active engines
In the Diesels it might be intended to reduce the NOx emissions, altough sacrifices some fuel-efficiency
  Reply With Quote
Old 11-08-2012, 03:26 PM   #10 (permalink)
Master EcoModder
 
Phantom's Avatar
 
Join Date: Jan 2010
Location: Independence, KY
Posts: 603

Blue Meanie - '02 Volkswagon Golf TDI
TEAM VW AUDI Group
90 day: 48.52 mpg (US)

Wife's car - '05 WV Passat TDI

Rudy - '94 Chevy C2500
Thanks: 89
Thanked 47 Times in 44 Posts
Also the <s>Sky-activ</s>Ecoboost engines are cast iron so they will hold heat longer. At least last I read unless they decided to change and go the weight saving route.

__________________
I move at the speed of awesome.


"It's not rocket surgery!" -MetroMPG

Last edited by Phantom; 11-12-2012 at 04:33 PM.. Reason: wrong engine
  Reply With Quote
Reply  Post New Thread


Thread Tools




Powered by vBulletin® Version 3.8.11
Copyright ©2000 - 2024, vBulletin Solutions Inc.
Content Relevant URLs by vBSEO 3.5.2
All content copyright EcoModder.com