timing the same for headers set up? lack power?

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Mopar King

Mopar King

Beginner / Need of Help
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Hello, I was wondering what is the timing for a 1973 Plymouth Scamp Slant 6 -225? is the timing the same with Headers or should it be increase?

I was also wonder, is a one barrel sufficient enough for a header set up? or does it need to be converted to a 2 barrel?

I don't want to take away power. when my car didn't have the headers I gotten uses to its power but now since I made a full overhaul on almost everything and it is almost done I was wondering if the one barrel lacks power. I haven't test drive it yet but I have started it to let it warm up and test basic things like lights, Ect... let me know what you guys think. I will post picture of my scamp very soon...




 
from what ive heard about slant 6s is that they need some back pressure. my guess would be that the exhaust might be a little too free flowing. not sure about your muffler choice, or pipe diameter so this is just an educated guess. as far as timing, you can always try bumping it up a little.dont think header would affect it though.
 
you engine is probably running lean now that you have installed headers...
 
Justin H. : My pipe circle diameter is 2 1/2 inches wide and the pipe exiting from the muffler is 2 inches long. My muffler choice I think it is called "Super Sonic". I'll take a couple pictures soon


about the back pressure thing, what does it mean? I would like to learn more about this. I would like my scamp to run smooth and strong as possible.
 
The slant does not need back pressure. Plenty of folks run straight out the headers at the track.

What it does need is proper scavenging effect. How big are the primaries of your headers? It's possible to go too big and lose velocity of the exhaust gas charge.

Wrap will get some of that back. As the gasses cool, they slow down. Keep the temperature, and therefore the velocity up as long as possible. In effect this causes a low pressure to be present at the exhaust valve, since the gasses have mass. This contributes to drawing charge into the cylinders during the overlap event. A tuned length header with appropriately sized primaries will be very happy. :-D

There are folks running 1bbl setups with headers to good effect, but they've bumped compression. your going to want 9:1 or so to make effective use of them. What carburetor are you using? If it's a Holley, you can bump your jet up a size or three. With headers on a 1920, a 59 to 61 will liven things up a bit. Be careful though, or your economy will tank.
Now that your playing with things, your going to want to work on your distributor. 10 deg initial, a 9R governer, and you might want to put a tad lighter "Light" spring on the mechanical. Just make sure the spring perch is appropriately adjusted to avoid problems with rpm drop going from Park to Drive. If the spring is loose on the perch, you will have to carry a lot of Neutral idle rpm.

Gear ratio and converter stall are also good ways of waking the old girl up.

CJ
 
No engine needs backpressure (backpressure is pressure that builds up in the exhaust system). ANY energy used to push exhaust out is energy that can't be used to turn the tires. Headers commonly scavenge enough better on a low performance engine to cause it to run lean with the factory carb. Or, to put it another way, you are now moving enough more air through the engine that the carb can't flow enough gas to keep up.

Is a 1bbl sufficient for the header setup? With a larger main jet, perhaps, but it will be your limiting factor. It sounds like you have plenty of exhaust system now. Your car would certainly run better with a 2bbl or perhaps even a small 4bbl. This would mean a manifold change including linkages..

As for timing, experiment with advancing it. Start out at 5 degrees BTDC or so. Whatever the middle timing mark is. Test drive. Now advance to the outer timing mark. Test drive. Is it better? If so, advance by that much again, moving the mark off scale by the same amount you advanced it last time (like 3/8 inch or so). Better? Do it again. Worse? Go back and home in on the best setting. You can probably run 10-15 degrees initial in a slant with no problem. Obviously, if it starts pinging, your are at the limit of advance.
 
I tried taking pictures today of the mufflers but didn't work so well. I'll try again tomorrow. I did get a couple of pics that came out alright.

I forgot to mention that the muffler system is Dual mufflers. they are coming out of each tire's side as seen in picture. Does it affect its performance. I am also still using the same old carb. I haven't bought a new one yet but will soon.






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Nice. Big RED engine!

Jet up the carb. The headers are extracting or letting more of the spent air and fuel charge out. The result is more room to draw in fresh air and fuel. Your getting more air, not the fuel.

The exhaust pipe seems a bit big to me.

I don't know if the 1 bbl. is enuff. Did you do any other MODs?
 
The one bbl carb will probably be ok up to about 4000 rpm if it's jetted right. The header and exhaust size looks ok to me, backpressure is for 2 stroke engines like dirtbikes and chainsaws. As for the timing, every engine is different so to get the most power is going to take some trial and error. I would advance it till it pings under full acceleration then back the timing off until the pinging stops. This usually throws the timing off at idle speed so you'll probably have to pull the distributor and play with the timing curve by changing the advance springs.
 
back pressure makes power below the engines power band or picks up the torque under the cam.

who races below the engines power band?

street cars.


with low back pressure you'll have to richen it up.

the scavenging of the header is pulling the bah-gee-zuz out of that 1 barrel, jet up.
if you have any cam bigger than 252*, even the factory 2 barrel won't due with lil jets available.

I recommend a holley 350 cfm 2 barrel, or up the jet size and live with it.

jmo
 
I don't think he's racing it....is he?
 
it applys to around town driving and the diff between mashing it to move or actually having the torque to get out of your own way.

2 1/2 exhaust is on the big side, 2- 2 1/4 is what I would run.
 
By adding a header you have increased the volumetric effeciency of the cylinders (more hot gasses escaping on the exhaust stroke because of less back pressure). Less chance for detonation, so less pinging and more timing. There will also be more air on the intake stroke so it will need more fuel, so a bigger carb with proper jetting will help.
 
Rumblefish 360 : Thank you for the compliment. its alittle dirty from restoring everything in its place. The headers need to be repainted. a Learning newbie mechanics :read2: + with my dad's help :glasses9: - our job is never done . the reason the pipes are 2 1/2 is because of the headers and the mufflers. for the Mods, nope - everything is mostly all original stock except for the headers. not performance racing just cruising around or riding highways.




1wild&crazyguy: I'm not racing even though the car saids different 8). are you sure a normal two barrel isn't enough powerful. I was going to go with that super six set up, if I can find the set up. the Holley 350 sounds very interesting but a little worried for my aging Slant six engine.



I don't know how to jet carbs yet. I got to learn how to do that. I'll try to keep you guys posted but now I have to replace both tie rods from each side, brake pads and other stuff before letting her out again. here is a picture of her


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A carter bbd will not be enough. The stock holley will be OK since you can tune it. The 350 will be optimal.
 
Mopar King said:
1wild&crazyguy: I'm not racing even though the car saids different 8). are you sure a normal two barrel isn't enough powerful. I was going to go with that super six set up, if I can find the set up. the Holley 350 sounds very interesting but a little worried for my aging Slant six engine.



I don't know how to jet carbs yet. I got to learn how to do that. I'll try to keep you guys posted but now I have to replace both tie rods from each side, brake pads and other stuff before letting her out again. here is a picture of her


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Why does everybody confuse what I say....
all I did was tell you where the back pressure helps you in the rpm range and now a few of you think it's only race related???????????

good luck, you're gonna need it.
 
1wild&crazyguy said:
Why does everybody confuse what I say....
all I did was tell you where the back pressure helps you in the rpm range and now a few of you think it's only race related???????????

good luck, you're gonna need it.
Click to expand...

haha remember what we went thru??!! hhaha thanks for the help by the way!

now to the posty!

those look like hooker super comp headers. plenty big primaries 1 5/8" , as for the exhaust u can buy reducers from the 2 1/2 flange of the headers to a 2.25 pipe. i would step up to a bigger carb like a super six set up.

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The 1bbl will work fine if properly jetted. You will want to redo the head(bigger valves and some port work Shave it)next. THEN move on to a 2 bbl or small 4 bbl.
Frank
 
66aCUDA said:
The 1bbl will work fine if properly jetted. You will want to redo the head(bigger valves and some port work Shave it)next. THEN move on to a 2 bbl or small 4 bbl.
Frank
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Frank not sure what your experience is,but wih my 67, stock 225 with a clifford full length header and a 1 bbl it didnt work no matter what jet I used.Even a 61 jet in the 1920 did not work.Idle was great,stinky but ran smooth,as soon as I would breathe on the throttle it would go lean and surge.I would recommend some kind of tune able 2 bbl or 4 bbl.Just a jet change wont cut it.
 
I wouldn't wait, I get the 350 2brl or 390 4brl now.

How big a jet you need 'could' exceed the bleed / eco valve and really not have you in much better shape, and besides...you don't need big valves to realize the benefits of the bigger carb and that 1920 was good...but back in the hayday not 'today'.jmo

btw love the name 'mopar king'.... with the title 'beginner/novice' under it.lol
 
Grinder said:
Frank not sure what your experience is,but wih my 67, stock 225 with a clifford full length header and a 1 bbl it didnt work no matter what jet I used.Even a 61 jet in the 1920 did not work.Idle was great,stinky but ran smooth,as soon as I would breathe on the throttle it would go lean and surge.I would recommend some kind of tune able 2 bbl or 4 bbl.Just a jet change wont cut it.
Click to expand...
With 1 bbl 1920's I converted several Dusters from the 1945 carb to the 1920. I could never seem to get the 1945's to run right. NOT all 1920 are good (or even ok) as I have thrown a BUNCH in the scrap bin over the years.
I used to super six ALL my slants (except the race engines) but have found that some cars like the 1bbl much better.
Did you just change the jets or did you mess with the air bleeds and such? I have had some real problems with the smog versions and plugged passages.
Frank
 
I agree the '45s are junk.The 1920 is a great carb. They can go bad,but I havent seen any new ones that were 'wacky' like '45s out of the box(new)

I changed the jet,i played with the air bleeds, tuning by seat of the pants and by plugs.Messed with timing etc... The 1 bbl is just simply not enough CFM for the motor any longer after the install of headers. I would even say the bbd and 2280(is that the stock slant 2 bbl holley?) is not enough,but they will work.
 
Its the lack of tune ability or parts to tune, like the thermo quad in a way.

gotta remember...that carb [holley 1920] was chosen to work with the coffee straw exhaust and not used in 5000 rpm with big tubes pullin the baageezuz out of it.

though i'm sure you could stick filed down paper clips into the bleeds to make them smaller...
 
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