89.Fifth
Well-Known Member
I'm still not sure which ones could possibly work on our cars but I don't think I want to go the headers route yet.
Will these Magnum manifolds work?
- Thread starter 89.Fifth
- Start date
Keep your 318 manifolds as there is barely any discernable difference in flow rate between ALL small block manifolds. Up to 300 hp none of them are a bottleneck and after that they all are.
After 300 hp a set of shorty headers is the best compromise. Personally I'll never run long tube headers again.
After 300 hp a set of shorty headers is the best compromise. Personally I'll never run long tube headers again.
89.Fifth
Well-Known Member
Thanks. I've seen someone running shorties on these before. Do all A-Body shorties fit?
Well, A-body long tubes fit, so I would guess the shorties do. Gear box is in the same place.
That is a pair of Jeep Grand Cherokee Magnum manifolds.
To the original question, those manifolds will fit and work fine with a couple of exceptions:
- The exhaust connection will be in slightly different position – so some minor exhaust work will be needed.
- The A.I.R. ports on your cylinder heads will need to be plugged first (if applicable).
- Need to find a way for a heat manifold – if you plan on driving a lot in frozen temperatures (32’ F / 0’ C).
The A.I.R. ports look like:
Not a very good picture.
If you are looking for less maintaince and less noise than headers, those would be the most cost-effective version if you are at/in 300 HP or thereabouts range, that fits an FMJ.
BudW
To the original question, those manifolds will fit and work fine with a couple of exceptions:
- The exhaust connection will be in slightly different position – so some minor exhaust work will be needed.
- The A.I.R. ports on your cylinder heads will need to be plugged first (if applicable).
- Need to find a way for a heat manifold – if you plan on driving a lot in frozen temperatures (32’ F / 0’ C).
The A.I.R. ports look like:
Not a very good picture.
If you are looking for less maintaince and less noise than headers, those would be the most cost-effective version if you are at/in 300 HP or thereabouts range, that fits an FMJ.
BudW
89.Fifth
Well-Known Member
Thanks for answering my original question. When you say heat manifold, do you mean that spring loaded heat riser, or the little unit that runs a pipe to the air cleaner?
The rest should already be taken care of. I have a motor that's been worked on that might be going in.
Well, I, um, forgot about the heat riser as well (the spring-loaded flap on passenger side manifold.
The Magnum engines do not use the exhaust crossover in the intake – so heat riser no longer serves a purpose on Magnum engines. They also don’t have the heat stove on the driver’s side manifold.
Heat riser
Heat stove (not a FMJ)
That said, if you have no plans on driving car when temperatures are at freezing (or lower) or using fuel injection, then neither item will matter much.
BudW
The Magnum engines do not use the exhaust crossover in the intake – so heat riser no longer serves a purpose on Magnum engines. They also don’t have the heat stove on the driver’s side manifold.
Heat riser
Heat stove (not a FMJ)
That said, if you have no plans on driving car when temperatures are at freezing (or lower) or using fuel injection, then neither item will matter much.
BudW
89.Fifth
Well-Known Member
I'm in New York so freezing is the norm in winter here. The heat stove never seemed to make much difference but I wonder if the heat riser really would. I guess it doesn't make much difference from a performance perspective right?
It seams the older I get, the more I forget (I think …).
All FMJ's use the heat stove on driver’s side.
Some of the V8’s made in the ‘80’s does not use a normal heat riser.
There is a short piece of cast iron, about 1” (25 mm) thick with a vacuum motor attached that is sandwiched between the passenger side exhaust manifold and Y-pipe flange. The vacuum hose/line that feeds that vacuum motor is part steel tubing and part rubber hose (to keep from melting from exhaust heat). One of the vacuum solenoids on firewall controls vacuum to this valve – which is officially called an “Power Heat Valve Assy.”
This valve is (another) problem part, that some will wire the valve into an open position. A person can convert it to a normal heat riser if you could find an inexpensive heat riser repair kit.
Personally, I’m not sure a working heat riser will make a hill of beans difference for most of us (except in emissions states). Yes, it does help get the engine to operating temp a smidge faster – but not that much faster. The heat stove will still work as designed and those with electric choke thermostats (99.9% of all FMJ’s have electric choke thermostats) so choke operation is mostly unaffected.
The reason I say this is most Chrysler V8 intakes (except for Magnum engines), the exhaust passageway in intake is already stopped up or restricted to the point little exhaust goes through it. I think the last dozen (or so) intakes I’ve removed, the exhaust passageways were stopped up. Cleaning those passageways is a royal pain to do.
I thought I had some pictures of stopped up exhaust passageways on my computer - but couldn't find 'em.
If your heat riser is currently working, great!
If "I" am working on a car with the heat riser is stuck (rusted or other), I will find a way to get heat riser valve open or cut out the flap inside of exhaust manifold. You can spend a lot of time getting a heater riser to work - and yet not get much (if any) benefit from the working riser.
The only exception to that might be on a high-end restoration car or a state that requires that system to operate correctly.
Otherwise, I say "good riddance", and don't damage my trash can on the way out of my garage.
BudW
All FMJ's use the heat stove on driver’s side.
Some of the V8’s made in the ‘80’s does not use a normal heat riser.
There is a short piece of cast iron, about 1” (25 mm) thick with a vacuum motor attached that is sandwiched between the passenger side exhaust manifold and Y-pipe flange. The vacuum hose/line that feeds that vacuum motor is part steel tubing and part rubber hose (to keep from melting from exhaust heat). One of the vacuum solenoids on firewall controls vacuum to this valve – which is officially called an “Power Heat Valve Assy.”
This valve is (another) problem part, that some will wire the valve into an open position. A person can convert it to a normal heat riser if you could find an inexpensive heat riser repair kit.
Personally, I’m not sure a working heat riser will make a hill of beans difference for most of us (except in emissions states). Yes, it does help get the engine to operating temp a smidge faster – but not that much faster. The heat stove will still work as designed and those with electric choke thermostats (99.9% of all FMJ’s have electric choke thermostats) so choke operation is mostly unaffected.
The reason I say this is most Chrysler V8 intakes (except for Magnum engines), the exhaust passageway in intake is already stopped up or restricted to the point little exhaust goes through it. I think the last dozen (or so) intakes I’ve removed, the exhaust passageways were stopped up. Cleaning those passageways is a royal pain to do.
I thought I had some pictures of stopped up exhaust passageways on my computer - but couldn't find 'em.
If your heat riser is currently working, great!
If "I" am working on a car with the heat riser is stuck (rusted or other), I will find a way to get heat riser valve open or cut out the flap inside of exhaust manifold. You can spend a lot of time getting a heater riser to work - and yet not get much (if any) benefit from the working riser.
The only exception to that might be on a high-end restoration car or a state that requires that system to operate correctly.
Otherwise, I say "good riddance", and don't damage my trash can on the way out of my garage.
BudW
