Random question.. intake exhaust crossover with headers ?

[rustytoolss]

Since my 318 has headers, how much heat would be going up into the exhaust crossover system? Since that system was meant to be used with manifolds and a heat riser. I know that most people seem to block the crossover port under the intake, but without a heat riser would the amout of heat be all that much ?

 

[Dana67Dart]

Not sure I understand your question.

Are you asking for you need to block the x over at the intake manifold if you are using headers that do not have a provision for the x over?

 

[rustytoolss]

What I'm asking is since I have headers , the heat that would have gone up into the exhaust crossover because of the heat riser...there sould not be as much heat (right), So would blocking off the crossover ports really be of much advantage on a daily driver.

 

[Murray]

Without a heat riser valve in place the heat getting to the intake manifold will be greatly reduced. This will cause the choke to open very, very slow. Since you are installing headers, I would recommend blocking the crossover port with the proper intake gasket and use a carb with an electric choke.

 

[413]

There will still be plenty of heat. The choke will work fine. I’d leave it open if you drive when it’s below 60 degrees.

what is the set up on the engine how do you drive, what do you do with the car?

I have a mild 440+6 with stock can and headers and the crossover open, I drive year round except snow. Car starts on a freezing morning and the choke and fast idle work just fine.

with the crossover plugged it’s a pig until you drive it for 20-30 minutes to get heat in the intake. A Big pain in the *** really. I don’t see the benefit, it’s not a race car.

 

[rustytoolss]

There will still be plenty of heat. The choke will work fine. I’d leave it open if you drive when it’s below 60 degrees.

what is the set up on the engine how do you drive, what do you do with the car?

I have a mild 440+6 with stock can and headers and the crossover open, I drive year round except snow. Car starts on a freezing morning and the choke and fast idle work just fine.

with the crossover plugged it’s a pig until you drive it for 20-30 minutes to get heat in the intake. A Big pain in the *** really. I don’t see the benefit, it’s not a race car.

Basically stock 318 with electronic ign,electric choke, headers, 3.23 gears, auto. Drive mostly april-november, somewhat of a DD on weekends, N.E. Ohio. Just want good dependable operation/ and good MPG (if possible)...by no means a race car !

 

[Dartnut]

Basically stock 318 with electronic ign,electric choke, headers, 3.23 gears, auto. Drive mostly april-november, somewhat of a DD on weekends, N.E. Ohio. Just want good dependable operation/ and good MPG (if possible)...by no means a race car !

As long as the heat crossover on the intake manifold isn't plugged, you should be good to go.

 

[AJ/FormS]

Headers have a specific job to do, which is to deliver a low-pressure signal to the back of the exhaust valve, at the exact right time so that just before it closes, and as the intake is simultaneously opening, this low pressure signal is transmitted across the top of the piston and into the intake plenum, where it yanks the A/F charge, that is "just waiting" in there, towards the chamber, giving it a head-start, on the intake stroke.
Now, if that crossover passage has NOT been blocked off, think what will happen?
Yes that low pressure signal will travel right thru the passage to the other header, thus destroying at least two signals, and knocking out 25% of the power that the overlap period would have brought to the table.
On a stock-cam 318 engine that's probably no big deal, cuz it only makes about 16* of overlap. But as the cam gets bigger, by the time you get to a 268/276/110; this cam is making 52* of overlap, which as far as overlap is concerned, is a lot.
With the crossover OPEN, IMO, the two pipes involved will just shuttle hot exhaust back and forth all the time, same as the logs do when the flapper valve is open.

 

[AJ/FormS]

but without a heat riser would the amount of heat be all that much ?

Well yes it will; your exhaust temp at idle will be near 400*F. It will only get hotter as the engine starts to work. Typically at WOT, temps can climb to hotter that 800*F.
That will NOT be the temp in the passage, altho it is common to find that chamber plugged with burned carbon, that came from the engine oil.

If yur looking for mpg, you gotta plug at the very least, MOST, of that port so it cannot cook your carb, and mess up your AFR. For your application as described, I would block it completely. AND, the carb should be getting fresh cold air from somewhere NOT under the hood. As long as it is sucking underhood air being cooked by the rad, the hot engine and especially the hot headers, Your AFR will be impossible to regulate properly. You do not need a scoop or a hole in the hood, just some ductwork past the radiator core support.
For an all-out mpg effort; your cruise-timing will need to be optimized. Yur gonna need a ton of it. Depending on your cruise-rpm, 50 degrees might not yet be enough. I have run my low-compression 318, into the 60s, with pretty good results.
With headers, your 318 may over-scavenge at too low a cruise rpm. You may find that it gets better economy at 2000 than at 1600, which, theoretically, should not happen.
To find the best cruise rpm, tee a vacuum gauge into the intake, then, in P/N slowly rev the engine up. As the rpm rises, the vacuum should also rise as the engine gets more efficient. Around 2400 with a stock cam, the vacuum might start to fall. Find the plateau of highest vacuum, and try to cruise as low as possible on it.
If you have 2.76 gears and 26" tires, this might be 65=2400. But if your cruise timing is only 24*, yur never gonna get decent mileage out of it. Not even at 34 degrees, and not even at 44* degrees.
To find your target cruise timing; in N/P, rev it up to your specific cruise rpm and hold it there while simultaneously advancing the timing; just pull on the can and close the throttle until more timing no longer produces more rpm. Now read your timing, and subtract 3*; that will get you a target to try to aim for. Reduce your rpm and reset your timing back to where it was before the test.
In all probability, at 2400 rpm this target will be over 50 degrees. I kid you not.
The engine is telling you what it wants. Now giving it to her will be the challenge.

 

[rustytoolss]

Well yes it will; your exhaust temp at idle will be near 400*F. It will only get hotter as the engine starts to work. Typically at WOT, temps can climb to hotter that 800*F.
That will NOT be the temp in the passage, altho it is common to find that chamber plugged with burned carbon, that came from the engine oil.

If yur looking for mpg, you gotta plug at the very least, MOST, of that port so it cannot cook your carb, and mess up your AFR. For your application as described, I would block it completely. AND, the carb should be getting fresh cold air from somewhere NOT under the hood. As long as it is sucking underhood air being cooked by the rad, the hot engine and especially the hot headers, Your AFR will be impossible to regulate properly. You do not need a scoop or a hole in the hood, just some ductwork past the radiator core support.
For an all-out mpg effort; your cruise-timing will need to be optimized. Yur gonna need a ton of it. Depending on your cruise-rpm, 50 degrees might not yet be enough. I have run my low-compression 318, into the 60s, with pretty good results.
With headers, your 318 may over-scavenge at too low a cruise rpm. You may find that it gets better economy at 2000 than at 1600, which, theoretically, should not happen.
To find the best cruise rpm, tee a vacuum gauge into the intake, then, in P/N slowly rev the engine up. As the rpm rises, the vacuum should also rise as the engine gets more efficient. Around 2400 with a stock cam, the vacuum might start to fall. Find the plateau of highest vacuum, and try to cruise as low as possible on it.
If you have 2.76 gears and 26" tires, this might be 65=2400. But if your cruise timing is only 24*, yur never gonna get decent mileage out of it. Not even at 34 degrees, and not even at 44* degrees.
To find your target cruise timing; in N/P, rev it up to your specific cruise rpm and hold it there while simultaneously advancing the timing; just pull on the can and close the throttle until more timing no longer produces more rpm. Now read your timing, and subtract 3*; that will get you a target to try to aim for. Reduce your rpm and reset your timing back to where it was before the test.
In all probability, at 2400 rpm this target will be over 50 degrees. I kid you not.
The engine is telling you what it wants. Now giving it to her will be the challenge.

This a stock cammed 1963 318 poly. (in a 1962 Plymouth Fury wagon) stock 727. 3.23 gears. 2 barrel intake (350 cfm carb) Mopar performance electronic Distributor (3690430) with adjustable vac can. Shorty headers dual exhaust 2" turbo mufflers. Rear tires are going to be 27.6"-28.1". Any different info would be great. Thanks, Merry Christmas.

 

[MopaR&D]

Since you don't drive the car in the coldest winter months I'd block the exhaust crossover and not worry about it. I blocked the crossover on the 360 in my '72 D200 pickup with an Edelbrock Performer intake manifold and I'm glad I did, running an Edelbrock carb with a 1" phenolic spacer it still occasionally percolates the gas in the bowls slightly. It probably takes a bit longer for the intake to warm up but even on the coldest winter days I've started it up and was on the road within 5 minutes.

I imagine back in the days before ethanol-blended fuel (which is also 'designed' for fuel injected engines) the heat crossover was pretty important. But modern E10 gas vaporizes so quickly and easily it's not a big deal to keep the intake hot anymore and it'll likely cause more bad than good. Only time I've experienced issues was running an Air-Gap intake on the last 360 in my Duster in 25 degrees (F) or less on the freeway; I would sometimes get carb icing with that setup. Now I'm running the same carb (Street Demon) still with no heat crossover but a non-Air-Gap RPM intake and the residual heat from the oil splash on the underside of the intake as well as heat transfer from the aluminum heads, it now runs very consistently and I have zero issues in super cold temps.

 

[MopaR&D]

Adding to what I said, taking the time to tune your idle mixture, base ignition advance and adjusting the choke properly will help immensely in cold-weather driving. Not enough advance or too lean on the idle mixture (or vacuum leak), you'll be sitting for 10 minutes feathering the gas waiting for it to warm up even if the exhaust crossover is working.

 

[413]

Anybody ever experience a small block mopar plug the crossover and the engine run terrible. Then after removing the intake and cleaning out the passage it runs fine again?

just did that on a 360 this summer. I rebuilt the cab and checked out everything. Would run bad until it ran for 30 minutes and get heat in the intake. Then run fine. The crossover was plugged solid. Car ran like a top after that and the choke worked as normal.

I tried plugging a crossover on a stockish 440 I was drag racing. It would go 14.0 at 98 mph with 3.55 gears and 28” tall tires. After plugging crossover the car didn’t go any faster and drive ability was compromised, again it ran bad unless it ran long enough to get the intake hot. It was the only change made.

Wrapping it up, I’m not a fan of plugging the crossover on a stock engine.

If you have percolating fuel put on a wood spacer, keep the fuel line cool, or use non ethanol fuel, but seems to work for me when the floor of the intake is warm.

now a race engine with 11:1 compression and a big cam and carb it works fine. Those race intakes don’t even have a crossover made into them.

 

[AJ/FormS]

Shorty headers

In your application, the shorty headers are acting more or less just free-flowing logs.
And with 3.23s and say 28s, 65= about 2600 rpm.
Everything else I said still stands with one minor diifference; at 2600 it will be easier to give the engine half decent cruise-timing.
Your Mopar Perf distributor has a single straightline advance curve of about 20* . If that is correct then the about best you can do with that will be say 12* idle timing/ 32* power timing. With a 2bbl and 9.2 Scr, you might be able to get away with 36* at 3400rpm on 87E10. BUT
I have never tuned a Poly, so IDK how much timing it will tolerate nor how soon. Below is a curve that should be a good place to start.

> I suggest to install 24* into the Distributor, and set the Power-timing to 36 degrees maximum at whatever rpm; which should give you 12* at idle.
>Then you will have to slow the rate of advance to about 1 degree per 100rpm or so. If it starts at 1000 rpm it will finish at about 3400.
>This means that at 2600rpm cruise, your mechanical timing will be;
{(2600 less 1000) x1* per 100}plus 12= 28 degrees.
The cruise-timing target may be as much as 52*.
Therefor your Advance-can needs to bring in about
52 less 28 =24 degrees. To do this, the external stops on the arm will have to be whittled down quite far. I got 22* out of mine. @TrailBeast got 24 out of his.
The trick is to not make all the changes at the same time.
> once you are ballparked, Disconnect the V-can and see if you can bring the Power-timing in sooner and or faster.
> do not get carried away with Idle-timing; It is IMPOSSIBLE to give the engine the idle-timing it wants, while simultaneously being able to drive it normally without detonation. The 12* quoted should get the transfer slots of your carb nearly shut off, at a typical idle of 500/550 in gear. If you get a tip-in stumble, increase the idle speed until it goes away. If the idle speed gets uncomfortably high, like 750 in Neutral, Retard the Idle timing a few degrees.
Get your Idle systems working before attacking the Distributor. Else you will end up redping the Power-Timing.
> Do not fall for the idea that your Power-timing has to be at some specific number or at some specific rpm. Here's why;
Even if your Power-Timing was 100% optimized,
It will only be correct with the throttles at WOT, and usually only over a very narrow rpm range, and even in a specific gear.
At all other load settings, and rpms,, it will be between a little wrong to impossibly lousy.
This curve is/should be, the MAXIMUM your engine can stand at WOT, less a a couple of degrees, for "just-in-case".
The rest of the time, your V-can should be providing the difference between what the mechanical curve is giving you and what the engine actually wants. Not what it will tolerate.
>More is Not always better. Two or even three degrees less than optimum Power-Timing is better than one degree too much; detonation must be avoided at all costs.
> The Poly engine is a solid-lifter design. The factory specs are for an engine at a given temperature. If you run your engine warmer or cooler than the spec, you may be able to/ may have to; change the spec. The on-seat time is the cooling system of the valves. My advice is; it's better to be a tad loose than a tad tight. Hot valves can be a source of pre-ignition which usually leads to detonation.
> For fuel economy, I run my engine as hot as I dare; 205* seems to be just right for my combo.
> Chasing fuel-economy can be fun....... but can also be very labor intensive as you go thru the motions of trying one thing after another. It can take several summers to reach the "close enough" point. The Poly is a great design and worthy of the time, IMO. Your three greatest tools are; Rpm, Throttle-opening, and cruise timing. After that is temperature. This assumes the engine is NOT sucking hot underhood air.
> High-octane gas has additives in it that slow combustion down to help prevent detonation. If your engine doesn't need help, don't run it. At cruise-rpm it is a big waste of money, and the slower burn time is not conducive to better fuel economy.
> pick the lowest octane fuel that your engine will not detonate with at WOT with full power-timing, and tune her to run it.
How will you know?
Wait until you tank is empty, then put enough 87 gas in it so that it is at least 90% 87. Set your Power-Timing to 36* at no sooner than 3600rpm. Now roadtest it. Get it up into Second gear/3400. Then begin accelerating and when you get close to 3600, floor it while looking/listening for detonation.
3600 in Second gear with 3.23s and 28s will be around 58 mph; 4000 will be 64/65 and is fast enough. If it downshifts into First, you will have to eliminate that.
Once you have a no-detonation baseline; you can experiment with more or earlier WOT Power-Timing.
If it detonates with 87 at 36* no earlier than 3600, something is probably wrong. The first thing to consider is a carbon build-up in the chamber, or too-hot sparkplugs..
Happy HotRodding

 

[rustytoolss]

In your application, the shorty headers are acting more or less just free-flowing logs.
And with 3.23s and say 28s, 65= about 2600 rpm.
Everything else I said still stands with one minor diifference; at 2600 it will be easier to give the engine half decent cruise-timing.
Your Mopar Perf distributor has a single straightline advance curve of about 20* . If that is correct then the about best you can do with that will be say 12* idle timing/ 32* power timing. With a 2bbl and 9.2 Scr, you might be able to get away with 36* at 3400rpm on 87E10. BUT
I have never tuned a Poly, so IDK how much timing it will tolerate nor how soon. Below is a curve that should be a good place to start.

> I suggest to install 24* into the Distributor, and set the Power-timing to 36 degrees maximum at whatever rpm; which should give you 12* at idle.
>Then you will have to slow the rate of advance to about 1 degree per 100rpm or so. If it starts at 1000 rpm it will finish at about 3400.
>This means that at 2600rpm cruise, your mechanical timing will be;
{(2600 less 1000) x1* per 100}plus 12= 28 degrees.
The cruise-timing target may be as much as 52*.
Therefor your Advance-can needs to bring in about
52 less 28 =24 degrees. To do this, the external stops on the arm will have to be whittled down quite far. I got 22* out of mine. @TrailBeast got 24 out of his.
The trick is to not make all the changes at the same time.
> once you are ballparked, Disconnect the V-can and see if you can bring the Power-timing in sooner and or faster.
> do not get carried away with Idle-timing; It is IMPOSSIBLE to give the engine the idle-timing it wants, while simultaneously being able to drive it normally without detonation. The 12* quoted should get the transfer slots of your carb nearly shut off, at a typical idle of 500/550 in gear. If you get a tip-in stumble, increase the idle speed until it goes away. If the idle speed gets uncomfortably high, like 750 in Neutral, Retard the Idle timing a few degrees.
Get your Idle systems working before attacking the Distributor. Else you will end up redping the Power-Timing.
> Do not fall for the idea that your Power-timing has to be at some specific number or at some specific rpm. Here's why;
Even if your Power-Timing was 100% optimized,
It will only be correct with the throttles at WOT, and usually only over a very narrow rpm range, and even in a specific gear.
At all other load settings, and rpms,, it will be between a little wrong to impossibly lousy.
This curve is/should be, the MAXIMUM your engine can stand at WOT, less a a couple of degrees, for "just-in-case".
The rest of the time, your V-can should be providing the difference between what the mechanical curve is giving you and what the engine actually wants. Not what it will tolerate.
>More is Not always better. Two or even three degrees less than optimum Power-Timing is better than one degree too much; detonation must be avoided at all costs.
> The Poly engine is a solid-lifter design. The factory specs are for an engine at a given temperature. If you run your engine warmer or cooler than the spec, you may be able to/ may have to; change the spec. The on-seat time is the cooling system of the valves. My advice is; it's better to be a tad loose than a tad tight. Hot valves can be a source of pre-ignition which usually leads to detonation.
> For fuel economy, I run my engine as hot as I dare; 205* seems to be just right for my combo.
> Chasing fuel-economy can be fun....... but can also be very labor intensive as you go thru the motions of trying one thing after another. It can take several summers to reach the "close enough" point. The Poly is a great design and worthy of the time, IMO. Your three greatest tools are; Rpm, Throttle-opening, and cruise timing. After that is temperature. This assumes the engine is NOT sucking hot underhood air.
> High-octane gas has additives in it that slow combustion down to help prevent detonation. If your engine doesn't need help, don't run it. At cruise-rpm it is a big waste of money, and the slower burn time is not conducive to better fuel economy.
> pick the lowest octane fuel that your engine will not detonate with at WOT with full power-timing, and tune her to run it.
How will you know?
Wait until you tank is empty, then put enough 87 gas in it so that it is at least 90% 87. Set your Power-Timing to 36* at no sooner than 3600rpm. Now roadtest it. Get it up into Second gear/3400. Then begin accelerating and when you get close to 3600, floor it while looking/listening for detonation.
3600 in Second gear with 3.23s and 28s will be around 58 mph; 4000 will be 64/65 and is fast enough. If it downshifts into First, you will have to eliminate that.
Once you have a no-detonation baseline; you can experiment with more or earlier WOT Power-Timing.
If it detonates with 87 at 36* no earlier than 3600, something is probably wrong. The first thing to consider is a carbon build-up in the chamber, or too-hot sparkplugs..
Happy HotRodding

Thanks ( I also have never worked with a poly engine ) merry Christmas