6=8 and bore over?

[C Galloway]

I have a 71 demon 225. The 6 starts and runs, but only runs decently for about 35 mins then starta crapping out. Anyways my variety of gear head friends have differing opinions of motor choices. Some says do and LS swap, some say find an old v8 rebuilt it and swap out. LS swap besides being near sacrilege sounds too complex, involved and spendy. Old mopar v8 seems do able, but also spendy. My idea... clifford 6=8 kit, rebuild motor, maybe bore over and shift kit for tranny, if thats an option for the 3 speed. My limitations are max 6k$. Body and interior is done enough to my satisfaction, but chassis, suspension is all stock. And tends to drift around a bit more then id like on the highway. So 6k max is what ill have to make this car more then just a looker. Anyone do a 6=8 kit? Like it? Worth it? Opinions welcome thanks

 

[Jorge Ramirez]

I have a 71 demon 225. The 6 starts and runs, but only runs decently for about 35 mins then starta crapping out. Anyways my variety of gear head friends have differing opinions of motor choices. Some says do and LS swap, some say find an old v8 rebuilt it and swap out. LS swap besides being near sacrilege sounds too complex, involved and spendy. Old mopar v8 seems do able, but also spendy. My idea... clifford 6=8 kit, rebuild motor, maybe bore over and shift kit for tranny, if thats an option for the 3 speed. My limitations are max 6k$. Body and interior is done enough to my satisfaction, but chassis, suspension is all stock. And tends to drift around a bit more then id like on the highway. So 6k max is what ill have to make this car more then just a looker. Anyone do a 6=8 kit? Like it? Worth it? Opinions welcome thanks

I have a 71 demon 225. The 6 starts and runs, but only runs decently for about 35 mins then starta crapping out. Anyways my variety of gear head friends have differing opinions of motor choices. Some says do and LS swap, some say find an old v8 rebuilt it and swap out. LS swap besides being near sacrilege sounds too complex, involved and spendy. Old mopar v8 seems do able, but also spendy. My idea... clifford 6=8 kit, rebuild motor, maybe bore over and shift kit for tranny, if thats an option for the 3 speed. My limitations are max 6k$. Body and interior is done enough to my satisfaction, but chassis, suspension is all stock. And tends to drift around a bit more then id like on the highway. So 6k max is what ill have to make this car more then just a looker. Anyone do a 6=8 kit? Like it? Worth it? Opinions welcome thanks

 

[Deemo]

I'm rebuilding a /6 225 for my Valiant. Clifford performance makes some good kits. But head on over to slantsix.org, tons of people over there have the part numbers, bores, decking and so forth with numbers to go with. Also Doug Dutra makes some fantastic articles. And why not turbo it? I'm seriously thinking of 8-12 lbs of boost on this one. Can make for a pretty mean and nasty /6 that'll shock the friends.

Search the forums, read the articles. And go with what you want. V8 or /6. Can't go wrong
Articles

 

[273]

Stock running magnum 5.9 or 5.2 regasketed is a good cheap starting place.

 

[Princess Valiant]

If you decide to rebuild the slant, it might be a good idea to diagnose it properly.

If it runs good then dies out after 35 minutes, then a rebuild may or may not solve your problem. It sounds like another factor is the problem. If the engine needed a rebuild, it more likely would never run decent at all.

Does it smoke, have you done a leak down test??

Can you set the timing accurately??

A rebuild or engine replacement sounds like it might be a shot gun diagnosis

 

[krazykuda]

You could have a v-8... I would go 318 or 360...

 

[BrianT]

If you decide to rebuild the slant, it might be a good idea to diagnose it properly.

If it runs good then dies out after 35 minutes, then a rebuild may or may not solve your problem. It sounds like another factor is the problem. If the engine needed a rebuild, it more likely would never run decent at all.

Does it smoke, have you done a leak down test??

Can you set the timing accurately??

A rebuild or engine replacement sounds like it might be a shot gun diagnosis

EXACTLY. Fix what you have first. You're gonna be awful disappointed if you replace the engine and it turns out that there is a problem with the fuel line collapsing or some similar problem. After you getting it running properly and tuned up, I would work on the brakes and suspension. They are 46 years old and were barely adequate when it was new. I'd look at replacing the rubber bushings, ball joints, shocks and maybe even the torsion bars and rear leafs. Make the car solid and safe before you start putting more power to it.

 

[Charrlie_S]

EXACTLY. Fix what you have first. You're gonna be awful disappointed if you replace the engine and it turns out that there is a problem with the fuel line collapsing or some similar problem. After you getting it running properly and tuned up, I would work on the brakes and suspension. They are 46 years old and were barely adequate when it was new. I'd look at replacing the rubber bushings, ball joints, shocks and maybe even the torsion bars and rear leafs. Make the car solid and safe before you start putting more power to it.

Exactly.
For a $6k budget, on mechanicals you can have a really nice running/driving car. Especially if you do the work, yourself.

PS: I would only use Clifford for Intake manifold, and/or headers. but don't worry about them, yet.

 

[nm9stheham]

The drifting around on the highway sounds like the typical worn front suspension bushings, steering linkages, and maybe steering box.

Can you describe a bit better what is meant by 'crapping out' after 35 minutes?

 

[KosmicKuda]

A 71 Demon is a desirable car.
An LS swap makes it not desirable.
Much easier to stay all Mopar anyway, the junk bolts right in.

Re your roadability....front end components have to be in good shape before anything. I used the Moog problem solver offset upper control arm bushings in mine (installed to maximize caster) and had it aligned with 2 degrees positive caster. Do not use the old listed alignment specs. The car, with radials, tracks down the road hands off like a freight train. If you have bias ply tires there's no hope.

 

[pauly]

The drifting around on the highway sounds like the typical worn front suspension bushings, steering linkages, and maybe steering box.

Can you describe a bit better what is meant by 'crapping out' after 35 minutes?

I agree with the drifitng around being, most likely, worn out bushings and such. If you are handy with things, you can rebuild an A body front end pretty inexpensively. Before you add more hp, make sure the car is handling decent first. Maybe add some stabilizer bars (front especially).

LS swaps seem to the latest craze these days. Personally, I wouldn't do this. If you want to have a modern motor, look for a low mileage Gen III Hemi. They, too, can get pricey, with the pieces and parts to complete the swap, but also an alternative way to get good hp at a reasonable price.

Don't shy away from a well built 318, 340, or 360 either. A magnum motor will run well too. Check the local Craigslist postings, as you never know what might pop up. I'm not real up on the /6 end of things, but know they can built up as well.

As stated before, check what you have first. It might be something easy to fix that will make it run much better. If you can live with it for a while, it will let you save up the $$ to made upgrades and maybe even a V8 swap.

 

[slantsixdan]

Be very careful before you decide to spend any money with Clifford. They have a long and ugly reputation for being a bunch of clowns; see for example here, here, here, here, and here. Much of what they sell is inaccurately described, and a lot of it is not even slightly cost-effective. The good news is that you don't need to go to Clifford to get hot rod parts for slant-6s; there are lots of other, better options. See for example Dutra Duals and header options discussed in this thread and this one, Erson custom cams, HEI ignition upgrade, Mike Jeffreys windage trays, Hurricane intakes, other exotic intakes. Hi-perf engine buildup here, high-perf parts and build info here.

 

[273]

I dont like the LS swap i get its cheap potential. But if it's all about best bang for the buck go buy a C5 vette not gonna make these old cars perform better for the money you can pick one these up. Or pick up a Chev body for the swap and have a cheaper around car. To me the engine is the soul of your car.

The only real advantage of these modern engines is that you can pick them up cheap and come stock with heads the flow same or better than race heads. Which is a big deal. But some act like a LA engine can't compare it's just got to spend money on heads that flow 250-350 cfm's for these engines unfortunately.

 

[AJ/FormS]

If it runs great for 35 minutes, then you just have a minor tuning issue.
6Gs is just enough to get yourself into trouble.
The engine is just the beginning. You will need everything behind it and in front of it and above it under it, just to stay outta trouble.
Oh, and I did all my own labor, and that is not reflected in the dinero.
But I did hire somebody to to the bodywork and paint, which is also not in the 17Gs

But I think we can help you with your tune.....

But if you have your heart set on retiring that slanty, then you can't go wrong with a Magnum. And if it's a 5.9,so much the better.

Since it says opinions welcome......lol, I wouldn't spend a nickle on a slanty, over a tune-up.

But I'll tell you what; I'm looking for a body to drop my HO 367combo into......and a 71 Demon is a prime candidate. Got pics?

 

[C Galloway]

If you decide to rebuild the slant, it might be a good idea to diagnose it properly.

If it runs good then dies out after 35 minutes, then a rebuild may or may not solve your problem. It sounds like another factor is the problem. If the engine needed a rebuild, it more likely would never run decent at all.

Does it smoke, have you done a leak down test??

Can you set the timing accurately??

A rebuild or engine replacement sounds like it might be a shot gun diagnosis

I did a compression test probably 10 years ago when i first picked it up, and i dont remember the exact numbers but i do recall them fluctuating betweens cycls and some beind under 80. You are right i should do the tests first to .see what im dealing with thank you

 

[C Galloway]

Be very careful before you decide to spend any money with Clifford. They have a long and ugly reputation for being a bunch of clowns; see for example here, here, here, here, and here. Much of what they sell is inaccurately described, and a lot of it is not even slightly cost-effective. The good news is that you don't need to go to Clifford to get hot rod parts for slant-6s; there are lots of other, better options. See for example Dutra Duals and header options discussed in this thread and this one, Erson custom cams, HEI ignition upgrade, Mike Jeffreys windage trays, Hurricane intakes, other exotic intakes. Hi-perf engine buildup here, high-perf parts and build info here.

Hey thanks, its some reason hard to find these companies and parts on a basic google search

 

[C Galloway]

The drifting around on the highway sounds like the typical worn front suspension bushings, steering linkages, and maybe steering box.

Can you describe a bit better what is meant by 'crapping out' after 35 minutes?

Well when i take the risk and drive it to work its a 30 min drive. If i stop off anywhere or traffic slows me up it starts stalling out. And it doesnt seem to be an overheating issue. For instance i drove it home from work and then went through taco bell drive through and it started stalling and had to keep the rpms up. And then when it dies from that its hard to start back up. I did a light carb rebuilt kit on it last year but is still having the same issues as before. Thanks

 

[nm9stheham]

OK, so is it accurate to say that the engine acts up when you have stopped or stopped moving after the engine is well heated up? If that is the case, then that sounds very much like the fuel heat soak issue that plagues these /6 cars in warm weather and with the new gasolines that are so much more volatile that in the old days. The gas in the fuel line in the engine compartment literally boils inside the line and it does not get proper fuel level into the carb.

There are several ways to cure and treat that problem. They include re-routing the fuel line up from the fuel pump over the valve cover instead of around the front of the engine, insulating the fuel line, a heat shield under the carb, and other such tricks. Also, make sure the exhaust manifold's heat flapper under the intake is closed. And it is discussed in several threads on this sub-forum; search for 'fuel line heat' in the Slant 6 forums. Perhaps others who have licked this problem will speak up.

 

[AJ/FormS]

To me it sounds like it could be a valve lash issue.

 

[slantsixdan]

Well when i take the risk and drive it to work its a 30 min drive. If i stop off anywhere or traffic slows me up it starts stalling out. And it doesnt seem to be an overheating issue. For instance i drove it home from work and then went through taco bell drive through and it started stalling and had to keep the rpms up. And then when it dies from that its hard to start back up. I did a light carb rebuilt kit on it last year but is still having the same issues as before.

Okeh, that doesn't mean you need to buy a bunch of upgrade parts or swap in a V8, it means it's time for some relatively minor, easy tweaks under the hood and a good, careful and complete tune-up.

Do the Fuel line mod. Make sure your fuel filter is reasonably new and not contaminated (and has a metal housing, not glass or plastic). Make sure the fuel tank and the in-tank strainer aren't full of crud.

Make sure your manifold heat control valve isn't stuck; see here. Make sure your thermostatic air cleaner is intact and working correctly.

Pay more attention to the carb than just a quicky gasket kit. The Holley 1920 carb that came on most '71 slant-6s contains a float that over time will absorb gasoline and grow heavy -- then the carb runs rich and causes problems like you describe here. Truth to tell, I really dislike the '70-'73 Holley 1920 carbs; they are especially prone to bitchy problems like this even if you throw a ton of effort and time into them. The '70-'73 Carter BBS, also used on some Slant-6s from the factory, is a much happier-running carb and its float won't absorb gasoline. "Remanufactured" carbs (of any make/model) tend to be junk not worth messing with no matter the price; if you can afford it, nothing runs like a new carburetor, and this one would be ideal (there's a "make offer" option on it, so maybe the seller will come down some).

Whatever carb you wind up with, carburetor operation and repair manuals and links to training movies and carb repair/modification threads are posted here for free download.

Tune-up parts and technique suggestions are in this thread, and you are probably due (or overdue) for a valve adjustment.

The '71 cars (plus '70 California) have a fuel vapour containment system that can cause or aggravate hot idle/hot stall problems. Read all about it (and what to do about it) here.

Beyond that, the first upgrade should be the HEI upgrade .

If some or all of this seems bewildering to you, get the three books described in this thread.

 

[C Galloway]

OK, so is it accurate to say that the engine acts up when you have stopped or stopped moving after the engine is well heated up? If that is the case, then that sounds very much like the fuel heat soak issue that plagues these /6 cars in warm weather and with the new gasolines that are so much more volatile that in the old days. The gas in the fuel line in the engine compartment literally boils inside the line and it does not get proper fuel level into the carb.

There are several ways to cure and treat that problem. They include re-routing the fuel line up from the fuel pump over the valve cover instead of around the front of the engine, insulating the fuel line, a heat shield under the carb, and other such tricks. Also, make sure the exhaust manifold's heat flapper under the intake is closed. And it is discussed in several threads on this sub-forum; search for 'fuel line heat' in the Slant 6 forums. Perhaps others who have licked this problem will speak up.

 

[C Galloway]

OK, so is it accurate to say that the engine acts up when you have stopped or stopped moving after the engine is well heated up? If that is the case, then that sounds very much like the fuel heat soak issue that plagues these /6 cars in warm weather and with the new gasolines that are so much more volatile that in the old days. The gas in the fuel line in the engine compartment literally boils inside the line and it does not get proper fuel level into the carb.

There are several ways to cure and treat that problem. They include re-routing the fuel line up from the fuel pump over the valve cover instead of around the front of the engine, insulating the fuel line, a heat shield under the carb, and other such tricks. Also, make sure the exhaust manifold's heat flapper under the intake is closed. And it is discussed in several threads on this sub-forum; search for 'fuel line heat' in the Slant 6 forums. Perhaps others who have licked this problem will speak up.

So incredibly helpful seriously, no one has ever brought that up. Im going to get on it this weekend.

 

[C Galloway]

Okeh, that doesn't mean you need to buy a bunch of upgrade parts or swap in a V8, it means it's time for some relatively minor, easy tweaks under the hood and a good, careful and complete tune-up.

Do the Fuel line mod. Make sure your fuel filter is reasonably new and not contaminated (and has a metal housing, not glass or plastic). Make sure the fuel tank and the in-tank strainer aren't full of crud.

Make sure your manifold heat control valve isn't stuck; see here. Make sure your thermostatic air cleaner is intact and working correctly.

Pay more attention to the carb than just a quicky gasket kit. The Holley 1920 carb that came on most '71 slant-6s contains a float that over time will absorb gasoline and grow heavy -- then the carb runs rich and causes problems like you describe here. Truth to tell, I really dislike the '70-'73 Holley 1920 carbs; they are especially prone to bitchy problems like this even if you throw a ton of effort and time into them. The '70-'73 Carter BBS, also used on some Slant-6s from the factory, is a much happier-running carb and its float won't absorb gasoline. "Remanufactured" carbs (of any make/model) tend to be junk not worth messing with no matter the price; if you can afford it, nothing runs like a new carburetor, and this one would be ideal (there's a "make offer" option on it, so maybe the seller will come down some).

Whatever carb you wind up with, carburetor operation and repair manuals and links to training movies and carb repair/modification threads are posted here for free download.

Tune-up parts and technique suggestions are in this thread, and you are probably due (or overdue) for a valve adjustment.

The '71 cars (plus '70 California) have a fuel vapour containment system that can cause or aggravate hot idle/hot stall problems. Read all about it (and what to do about it) here.

Beyond that, the first upgrade should be the HEI upgrade .

If some or all of this seems bewildering to you, get the three books described in this thread.

You couldnt be more helpful, truly. More knowledge then i ever expected to get about this. Cant say thanks enough.

 

[C Galloway]

Oh and one more thing about it acting up, could be part if the same issue. Like i said it starts up cold no problem, sometimes needs a touch of idling help for a second, but starts easy. But when i do, say take it to the convenient store down the street, and i shut it off while i go inside. When i come back it doesnt like to start and will run really rough for a while then slowly usually clears up and runs. Id imagine that must go along with what was already said but just thought id add it in there

 

[RustyRatRod]

I will also add this to Dan's great advice. If you replace or rebuild your carburetor without removing and cleaning and or replacing the fuel tank if need be, you are pissin in a fan. Unless the fuel SOURCE is clean, you will have continuous problems, no matter how much money you spend or how many parts you throw at it.