Alright, so I've built a Ford and several Chevys but I've never layed hands on a Chrysler v-8 with exception to basic servicing. Been looking through various websites to lean a tad more about the lil truck, but I seem to have an oddball. The 1991 LA318 Dakota. From what I've read, that's the same ol basic 318 that's been around since '67, but with a tweak or two. I'd like to do to this truck what I did to the driveline in my Mustang, but parts websites are contradicting to the info I have so far so I'm kinda stuck on what to do. From what I've read the lil Mopar I have is a factory roller motor with "fast burn" heads. I don't have a clue what transmission it has in it nor do I know anything about the durablility of the axle.


Here is the goal for the truck. I'm looking to closely match the performance and efficiency that I've gotten out of the Ford. My Mustang has been velocity matched, geared accordingly, and built to be as reliable as my budget could allow. She's 400hp, 423ft lbs of tq, and gets 27mpg on the interstate at 70mph. She'll run a high 7 second 1/8th mile pass, hangs a turn just as hard as an 04 Cobra and I have not yet been brave enough to find the top end. The little car runs out of speedo long before it runs out of peddle. It took 7 years to get that combination correct and I would love get as close as possible to duplicating that in my pickup. The overall goal is 24-25 mpg, 400 RELIABLE hp, and building the rest of the driveline to hold up to it for many years to come. I've already set the suspension to do what I need it to, and the ride on the Dakota is remarkably smooth. It is possible to hit those performance numbers as I've done it with a Ford and a Chevy. I just need more specific info so I can start tracking down the correct parts!


Thanks in advance, and I'm sorry for such a long first post!

 

Welcome to DF.

Yes you kinda do have the oddball engine setup. For the best details check out www.allpar.com

Since you have a LA V8 you have TONS of options for performance. www.summitracing.com
www.hughesengines.com
www.mopar.com/performance/index.html

Just remember just like any stock engine you will not get up to 400HP with out serious modification from the ground up.

There is a good article on 400HP on a 318. Check the FAQ in this section.

 

You will have a hard time getting 25 MPG with a truck with a drag coefficient of 0.49, unless your a duck tape master. As far as 400 ft lbs of torque (I do not look at hp figures), that is relatively easy with the stroke of these engines. The LA setups are better for higher output than the magnums, however, debateable. What is your interest as far as adding power? Compression, exhaust, heads, and cam are the real tweaks that I have seen. Same as any other engine.

 

I'm not really into it for "tweaks". I've been skimming over the FAQ sections and it's put me closer to the answer, but further at the same time. I now understand what type of creature I'm working with and some of the swap ideas (late model axle only 1" wider and super easy), but the figures are still off and the flow numbers I'm after don't look obtainable with the parts listed in outside links that I've found so far.

What I have in mind is something similar to the Comp Cam EE roller (565/574 232/240 112sep on 1.6s) if I can find or work a head that will flow around 250 @.500 or so, doing a pretty decent amount of refining to the block itself, matching up a piston to all of that and topping it off with a completely different fuel system. Most likely something close to a Fast EZ-EFI. I still need to do quite a bit of number crunching and parts researching to see what all I'll need to do to get there.

And yes, 25mpg is a pretty high goal for a 400hp truck. And yes, I would be fine with 20-22mpg, but that's not what I set out to do.



EDIT:
I think after a visit to the machine shop, there are a couple sets of heads over at Summit that meet the preliminary numbers that I was looking for. One of them is a Mopar head.... http://www.summitracing.com/parts/DCC-5153849/ Those have 2.02-1.60s in them. The 171cc runner might need to be slicked out, but I think it may work. I'm awake now, time to do some math....

 

You should get more comfortable with the idea of 18MPG at the very most and probably less.

 

Not to look down on the heads, but the Eddy's flow better OOB. The Mopar aluminum's are nice though. I have the small port 53cc type, but they did not include the complete valvetrain, unlike the Eddy's and the heads you mentioned.
To add to the MPG issue, I am aware that Corvette's, Camaro's, mustang, etc. get good gas mileage with good power, but they are not a brick face pushing through the air. An air dam will help, but unless my math is wrong you are looking at 21 MPG tops, with no accessory drives pulling a load, and not with an aggressive cam. To add insult, unless you swap the tranny to the 500 type (and modify to suit), your reciprocation mass is against you.

 

I built a Brick (78 C-10) that got 17mpg and there was nothing on the body of that truck aerodynamically efficient. That was the first one I did and that lil gem was still on a carb. I can do better with the Dakota. Seems to be a lot of naysayers through here. The driveline goals are going to be fairly easy, we shall see what data the road tests provide.

If it wasn't a challenge, it just wouldn't be fun.

 

A mostly stock v8 5 speed Dakota can do low 20s. A 400hp dakota with an automatic? Ain't happening dude. Especially with any decent stall or gears.

 

So if an inefficient vehicle can get into the 20s, why cant the same vehicle made much more efficient pick up a very easy 5 mpg? On another note, if that same vehicle had a little more rotational mass and was made to be much more efficient, then why couldn't it pick up atleast 9 mpg?

 

25% increase in fuel efficiency is a BIG undertaking. Also, you would want less rotational mass. I say go for it, and make some patents along the way. Just make sure you keep track of your data in detail.