Duster Idiot has shared his thoughts on this, but thought I should share the questions with the forum.

Goal is smooth idle and the best possible mileage. I have a line on another engine to build. It is a mid 80s hydraulic truck engine.

1. What combination of compression and cam will yield the best mileage? Am prepping a 3:1 rear now, but can change that in future. Still plan on GV OD with .8 OD ratio.

2. Is it best to go with stock valves and ports in truck head or use current engine's ported head with over sized valves? Torque and mileage are the goal. I was pretty aggressive with the porting, using a British book on porting in line engines as a guide.

Thanks for your thoughts.

Sam

_________________

You might want to remember the head design was not changed from the 170ci to the 225ci, bigger valves and a boost in compression wouldn't hurt.

Richard

_________________
Part of Tyrde-Browne Racing

engine builder sized valves (1.70 1.44)

Mild porting (cleanup on isle 2....) and port matching (not gasket matching, smooth transition or slight step up along gas flow direction)

Clean up the casting flaws in stock intake and exhaust manifold

Docs RV10 or RV15

8.5 to 9.0

2.25" exhaust

distributor recurve

_________________
Ed
64 Valiant 225 / 904 / 42:1 manual steering / 9" drum brakes

subscribed, what cam would be best for a solid lifter engine?

_________________
Dave

1977 d-200 crew cab ex-army pickup wants it's /6 back
1962 Valiant 2 door, 170, three on the tree
1972 d-100 parts truck
80 volare wagon now a parts car

Don't forget that mid 80's had 4 speed A833 OD aluminum case tranny as optin for you.

Dave

_________________
86 Miser 170,000+
2 1/4" exhaust
Holley 1920 #55
HEI MSD BLaster 2
17.8 mpg

Do you want absolute best economy or would you like the car to be fun to drive and economical?

_________________
Joshua

I think an overdrive with a 3.1 rear gear ratio will lug the motor badly. The highest gear ratio I recommend with an OD unit would be 3.5.

As I am sure you know, max MPG = low RPM and high torque. A while back board member Dadtruck did an extensive study on what hydraulic cam profiles made the best torque. If I remember correctly, he concluded that the stock hydraulic cam with an increased dynamic compression ratio was one of the best options available.

Ah, HERE is Dadtruck's thread.

_________________
Casually looking for a Clifford hyperpak intake for cheap.

It would be interesting to know how many folks have truly made better than 24 MPG hwy (at 60-75 MPH cruising speed) and what were those combos. That is a relatively small number of cars, I think. I also think those combos would be all over the map (CR, cam, valves, porting...).

DCR, AFR, and advance curve are probably the biggest variables. In other words, a big cam with high static CR can get you similar results to a small cam and low static CR, assuming AFR and ign advance curves are optimized. Obviously, you will make more power with a big cam and high static CR, but it will have a rough idle and you may want a somewhat taller (numerically higher) final drive ratio. Valve sizes and head flow should have much less affect on cruising mileage, but have a big impact on ultimate power.

Lou

_________________
Home of Slant6-powered fun machines since 1988

For what it is worth, this engine with the T-5 and a final drive ratio of 2.11:1 in overdrive, and the current RV cam produced 27 mpg on the highway coming back from Lou's place in august. It cruised nicely at 65 mph at 1800 rpm. However, it was never very efficient in local, around town service. It would routinely yield no better than 14-15 mpg. I suspect the ultra granny first gear ratio of 4.09:1 had something to do with that. It is in its comfort zone cruising below 2000 rpm. It will pull over 15" inches of vacuum all day on level ground revving 1200 rpm @ 30 mph. If I bump it into 2nd the rpms jump to 1800. It feels fine at that rpm, and the AF ratio actually goes leaner. But, the injectors are firing 50% more often. If I monitor the opening times of the injectors, I could probably work the math and find out if lugging is more efficient than spinning faster in second. But it seems perfectly happy to chug along at the low rpm. If it drops below 30 mph it will down shift on its own.

With the current lock up auto, and 2.71 rear, the best highway mileage I have managed is 19.9. In town it does 17 on a good tank.

Don't stop talking about this. I am all ears and eyes. I am reading the other threads as well. Thanks.

Sam

_________________

My set up easily gets over 24 mpg when I am not doing stop and go, short 4 mile hops. Then it nets 22.5 mpg. Any descent run over 8 miles nets excellent mileage. Long trips over the pass at 70 mph heavily loaded are 25+ mpg.
Higher compression for more torque is the key with my heavy 74 Swinger. Idle is super smooth especially in long 3 hour traffic jams.

Specs are below and engine build is in the Engine FAQ.

Key items are:
1. lots more compression
2. distributor recurve
3. and 2.5" exhaust which is ultra quiet......with Flow Masters
4. and lots of small items that help as well, used together help add up to better mileage.

_________________
Aggressive Ted

http://cid-32f1e50ddb40a03c.photos.live ... %20Swinger


74 Swinger, 9.5 comp 254/.435 lift cam, 904, ram air, electric fans, 2.5" HP2 & FM70 ex, 1920 Holley#56jet, 2.76 8 3/4 Sure-Grip, 26" tires, 25+MPG

Ted, I would be happy with your build, and your results. However, Lou's ideas are worth exploring. He has always gotten good results spinning a motor faster. And, Joshua, some fun would be OK. I am starting to read Dad Truck's thread on his build. There should be plenty of light shed on the subject there. It sounds like he has done some good spade work on this.

What about the idea that has been forth that too much porting will slow down the airflow at low rpms and contribute to less efficient atomization of the fuel? I remember that when I switched to the smaller injectors I had to reduce the numbers in the VE table to get the same AF ratios, which was completely counter intuitive. I theorized at the time that there was better atomization of a smaller fuel stream. I currently have 24 lb injectors in there, and have thought about going even smaller to maybe 18. That is another project for another day. Things run OK now, so I am leaving that end of things alone for now. This is just for for thought, or grist for the mill as they say.

SAm

_________________

Erik (mpgfanatic) told me his 64 Valiant (which I now have), got about 26-28 mpg on the highway. It has a 170 engine bored and honed .060 with a block plate, .005 deck, balanced, mildest Mopar performance solid cam, don't remember the head cc's, but a true 9.5 CR. stock valves, and 340 valve springs. Stock intake with a Holley 1920, and exhaust. When Erik had the car, it had point ign, I have converted it to HEI and do need to recurve the distributor, as it will ping on 87 octane at 10* initial advance. I don't know what ratio the rear is (really should check it). Three speed standard on the columm. Car is very peppy, but I have not had it on the interstate, just some local driving to cruises.

_________________
Charrlie_S
65 Valiant 100 2dr post 170 turbo
66 Valiant Signet 170 nitrous
64 Valiant Signet
64 Valiant 4dr 170
64 Valiant 4dr 225

Sam,
Go to the Engine FAQ, Engine Build Matrix, second entry....for my build.

HP fun is one thing with a lumpy idle, smooth idle and massive torque is another way having fun.
Lighting up both tires at a light right off idle......is great! When I drive nicely it gives super mileage and idles for hours perfectly in traffic.......

_________________
Aggressive Ted

http://cid-32f1e50ddb40a03c.photos.live ... %20Swinger


74 Swinger, 9.5 comp 254/.435 lift cam, 904, ram air, electric fans, 2.5" HP2 & FM70 ex, 1920 Holley#56jet, 2.76 8 3/4 Sure-Grip, 26" tires, 25+MPG

Sam you are right. There is more than one way to do things. Lou has always got good mileage and a fast car to boot. Not so sure about the ultra smooth idle, because I don't think he idles too much!!

Rick

_________________
2 Mopars come with Spark plug tubes. One is a world class, racing machine. The other is a 426 CI. boat anchor!

12.70 @ 104.6

I'll be interested to see how smooth is my idle on the 64 Dart when I go to multi-port EFI... I'm sure the exh at idle will always stink more than with a small cam. I am also pretty confident that my 64 engine makes more torque at 1500 RPM than a stock Slant. The tuneup (incl cam timing) must be right in order to get that.

Lou

_________________
Home of Slant6-powered fun machines since 1988