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Effect of bigger valves and bigger cam on gas mileage
https://www.slantsix.org/forum/viewtopic.php?t=17735		 Page 1 of 1
Author:  Reed [ Thu May 25, 2006 9:17 pm ]
Post subject:  Effect of bigger valves and bigger cam on gas mileage
I have an 86 Dodge van with a 225 and 904. THe motor puts out a huge cloud of blue smoke on startup, but none while driving. I am assuming this is due to worn valve stem seals. The van also gets abou't ten miles per gallon and has decent power.

I have in my garage a rebuilt cylinder head with oversize valves which has been ported. This is the head with the Ford 300 valves in int (1.7 and 1.44 I think). I also have a used Mopar Performance 244 camshaft in a box.

The motor has 147,000+ miles on it, but has good oil pressure so i am not worried about the bottom end.

Would it totally kill my gas mileage to swap the hydraulic cam out for the MP 244 cam and to swap on the big valve head? Would the increase in power make it worth it or would the power be in the wrong RPM range for a motor in a van? The motor spend most of the time between 2000 and 3500 RPM due to the 3.54 rear gears.

Will I end up just killing what little gas mileage I have? Or would these swaps wke the engine up and let me open the throttle less?

I also have a NOS Mopar Performance double roller timing set for a slant and the camshaft advance bushing set. Would it be worht it to swap these on to allow tunign of the motor?

Thanks! I don't think the motor needs a complete rebuild yet, but I would like to wkae it up a bit and hopefully get better gas mileage.
Author:  SlantSixDan [ Thu May 25, 2006 9:30 pm ]
Post subject: 
I don't think you need the big-valve head, but sounds like you have it. I also don't think that head and that cam will kill your fuel economy. If anything, that cam ought to improve driveability and performance. Remember you'll have to do the complete solid-cam-and-lifter changeover (lifters, pushrods, rocker shaft assembly w/rockers...).
Author:  CStryker [ Thu May 25, 2006 9:39 pm ]
Post subject: 
When I did my rebuild, I started with a stock but worn '82 225 with hydraulic cam, standard head, and crappy 1945 parts store re-man carb (never again!). I put in a 270 advertised cam, the oversized SI valves, and a 2300 Holley. Thus far, my highway fuel economy has remained unchanged, and there is significantly more power. What's killing me is my city mileage; it's taken a nose dive.

Realistically though, I attribute the majority of that to my driving style. Now that it's more fun to drive, I have a really hard time keeping my foot off the throttle. If I drove calmly and sedately, I'm willing to bet that my city economy would be unchanged as well.
Author:  mrbillohnooo [ Thu May 25, 2006 10:59 pm ]
Post subject:  Hiway rpm....cam brand?
Just out of curiosity, what hiway rpm does it run, and is the 270 adv. cam an erson?
I have an unported other than pocket work,big valve head and an erson 270 cam, but have been reluctant to install them on/in my slant six pickup for the sake of mileage.
Thanks!
Bill
Author:  Reed [ Fri May 26, 2006 6:55 am ]
Post subject: 
Dang, my typing was terrible in that last post.

Sounds like I will be doing this swap as soon as I get the time. I just need to get some new solid lifters and the head and manifold gaskets.

Can anyone tell me the recommended centerline for the 244 cam? Would advancing it help anything in this application?
Author:  CStryker [ Fri May 26, 2006 2:26 pm ]
Post subject:  Re: Hiway rpm....cam brand?
Quote:
Just out of curiosity, what hiway rpm does it run, and is the 270 adv. cam an erson?
I have an unported other than pocket work,big valve head and an erson 270 cam, but have been reluctant to install them on/in my slant six pickup for the sake of mileage.
Thanks!
Bill
Yeah, the cam is the Erson. Honestly, I haven't gotten around to installing the tach yet, so I can't give you an RPM for sure. Hopefully that's one of the things I'll get done this weekend. Keep in mind it's got the 3.23's out back, which isn't helpin anything (as far as mileage... sure dont' wanna give 'em up though . :D )
Author:  Dart270 [ Fri May 26, 2006 3:11 pm ]
Post subject: 
I have had the 244 at around 99 installed and 103 installed. I would put it 102-104 for best all around.

Lou
Author:  Reed [ Fri May 26, 2006 7:54 pm ]
Post subject: 
Thanks Lou!
Author:  zedpapa [ Fri May 26, 2006 11:06 pm ]
Post subject: 
you should have your torque converter checked. the tc in my car had the stator seize and caused really poor mpg. i think it will stall test ok but will take excessive throttle to maintain highway speed. a new converter i think is only $60 or $70.

zedpapa
Author:  Reed [ Sat May 27, 2006 7:59 am ]
Post subject: 
I am debating swapping the 904 that is in the van right now with the 999 I have in my garage. The 999 worked fine when I pulled it about five years ago, it just needed a new front pump seal which I replaced. It has sat on the floor in my garage ever since.
Author:  Pierre [ Sat May 27, 2006 10:48 am ]
Post subject: 
FYI - $60-$70 converters are NOT new, they are the remaned. Different strokes for different folks, but I would stay away from them with a 10 foot pole due to past experiences.
Author:  Reed [ Sat May 27, 2006 11:34 am ]
Post subject: 
How do i check the converter? Do I have to pull it and take it to a transmission shop?
Author:  zedpapa [ Sat May 27, 2006 8:25 pm ]
Post subject: 
no, just go drive and see how far you have to push the throttle down. to maintain 55-65 mph, you should only have to push the pedal down about a 1/4 way. if you half to push about halfway, the stator is seized and the engine is working too hard to maintain speed.

zedpapa
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