Hi, can anyone help me obtain more power out of my 6? It's in a 8000lb motor home. Gears 1 & 2 get me to about 22mph gear 3 to 35mph and 4th to about 50mph. if even a slight incline appears no power at all in 4th and anything steep its down to 2cnd and a lot of slow speed groaning, Cheers! Mark

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1968 Clark Cortez

Welcome to the forum!

There's power to be had, but your going to want to be careful when reviewing some of the builds. Many of the builds you'll find in the engine building Matrix located in the FAQ here are aimed at drag racing or making relatively light cars go faster.

Do a search for builds for trucks. I think the Cortez has come up a time or two as well.

If you hit the home button, then go to Articles you'll find a bunch of information there. It'll give you a better idea of what folks have done.

Look things over, and feel free to ask questions.

There is no one way to get the power you want, so you'll have to look things over and decide what best meets your power requirements, budget and so forth.

CJ

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Part of Tyrde-Browne Racing

What year is your Cortez?

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一期一会
Too many people who were born on third base actually believe they've hit a triple.

Cool vehicle. I don't know how you do it with a 6, though. I've got a 68 Travco with a 383, and I can't imagine trying to do really steep hills with it. My Travco's probably about 2000 pounds more than yours, but wow.

That seems like an incredible amount of weight to move with a Slant. I'm curious what can be done myself!

It's not all that bad. I've towed cars with a slant six and found myself zipping down the freeway at 65-70. Pickup (4600) + car dolly (350) + towed car ( 2500 ) is not far from 8000 of the motorhome. The biggest difference is the wind resistance, as a Cortez is just a big flat brick. As I understand it, the Cortez has about 5 something gear ratio, and with its size tires should get the slanter wound to somewhere around 3000 at 55-60.

Seeing as how I could pull a 4 percent grade with the car behind and stay above 45 up the hills, I see no reason the Cortez should not be able to make at least 35 up even quite steep grades.

I've even pulled 27 foot travel trailer from the 70's with a slant, and it would make 35-40 up the typical 5 percent interstate grades. The wind resistance was just as bad as the Cortez. The Cortez has an odd side draft 2 bbl carb, but I know nothing about its performance capability.

I've been looking for one of those Cortez MH's myself, with a slant six, just for the novelty - but don't have any money right now. I think I would try to convert it to propane and turbocharge it.

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'81 W150 on Propane... Oversize valves, Oregon Camshaft cam, 10:5 static CR, Distributorless ignition, megajolt timing controller, PowerTrax lockers.

I have a 66 Cortez but someone swapped out the /6 for a 318 at some point.... and I just swapped out THAT 318 with a 318 I freshly rebuilt. lol

The original Cortez slant sixes came with a 1bbl carter YH side-draft carb. The same one used on some Corvairs. Rebuild kits are still available.
Really the best way to get more power out of that particular industrial /6 is to make sure the valve are adjusted properly (.12-intake, .22-exhaust) and get the exhaust re-done to a larger diameter pipe with a free flowing muffler.

You can find a 2bbl super six set-up and put it on there but you will have to re-work/re-build the engine access lid between the driver/passenger seat to make room for the taller carb and the air cleaner duct attachment. My lid had been redone to accept the carb on top of the 318 and it looks like it was not too hard. Some cutting, bending and either welding or screwing of sheet metal and you can do it. The 2bbl carb will help a lot on moving that 8K pound beast. Especially with the addition of opening up the exhaust. If it's original... the exhaust is toooo small.

Actually I think mine is about 9000lbs loaded. And with my new 318 still gets me 14MPG.... on long flat roads. lol Still cheaper than getting hotels!! As long as I can afford gas.

The Cortez transmission is geared similar to my Dodge D100 pick-up's trans. Deep granny first, normal 2nd and 3rd. Overdrive 4th is a big step from 3rd but it's good on the freeway.... as long as you're going on flat land. The second you hit a hill bigger than a 2-3% grade the gearing is just too steep in 4th and you will be forced to slow down to 35-40mpg and shift down to 3rd and scream your way up the hill/mild incline. With my 318 I can handle up to a 4-5% grade without downshifting to 3rd as long as the hill is not longer than a couple miles.... otherwise I loose momentum and have to downshift.

Just so you are aware that you are not alone.

-Marc

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1965 D100 225 slant 6, NP435 Utiline.

I have never been up close and personal, with a Cortez, so just some sugestions.
First make sure the engine is in good condition (do a compression check)
Then make sure the "tuneup" is right.
No sense doing anything till you know this.
If everything is good, and still want more power, as suggested, a free flowing exhaust, and possibly a better/larger carb.
Two other items will help, but not together (one or the other), but both are more involved.
Remove the head and mill it to get an honest 8.7-9.0 to 1 compression ratio. This will help torque/power/ mileage.
You could also do a basic/simple turbocharger system, but this can get a bit pricy.

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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