I am cutting and pasting this from the thread entitled "water in oil" because it has become a discussion of heat risers, and I am looking to generate a little more discussion...

This is from Willian in Atlanta

"Without sorting through all the details here I'll agree with everyone. The exhaust manifolds come in a 2 inch and 2 1/4 inch. The bigger one is on trucks and most cars. The bolts in the left exhaust manifold are about three inches long to accomodate the heat riser. The heat riser I have is 2 1/4 inch, has a flat gasket on top between it and the manifold and a doughnut between it and the exhaust pipe. These heat risers are available new from a company in Texas and your parts guy should be able to order it. I'll dig up that info tonight and post it here tomorrow. I am from Michigan (UP) originally and lived in Alaska for several years and wet cold Europe for about 20 years. Based on that experience I am firmly convinced thet these old trucks need heat in the motor as quickly as possible for driveability and fuel economy. In Georgia I use a 190 thermostat, exhaust manifold heat riser and a hot water heater under the carburetor (looks like a spacer with heater hoses connected to it). The heater under the carburetor heats and then maintains the temprature of the carburetor. I also use a big steel six blade fan with fan shroud and thermostatic clutch for even summertime cooling. I have never had a failure to start even here in the hot summer. In traffic (jammed commuter), my engine stays in the safe range around 190-205 or so. I don't use a hot air supply off the manifold but I will when I find the correct air cleaner housing and exhaust manifold heater box. This is way overdoing it I know, but I like to experiment. I think a 190 thermostat and any one of the other heat methods is sufficient in the South, Up north I think you need all the help you can get.
William in Atlanta"

This is my reply
Thanks, William.

According to my Ford parts man, the heat risers were on the 352 but not the 360/390, which is probably why I can find no mention of them for V8's in my 68 shop manual, since as you know, 67 was the last year for the 352.

My manifolds are off the truck, the ports are 2 inches tall, and both of them are carved out for donut gaskets, so a heat riser is not an option for me unless I switch manifolds. If someday I decide to do headers, the heat riser would be lost anyway.

I bought the snorkle and heat shield on ebay awhile back. The snorkle looks to be controlled thermostatically (sp?) as well as by vacuum, there is a vacuum attaching point on a vacuum actuated arm under the snorkle. I have two unused manifold vacuum ports, so I can hook up no sweat. I'm not sure it's working though, obviously, with the manifolds off, I'm not running the truck much...

Again, this is from William

"The heat riser was used on all FE's in cars and trucks. Some vehicles sold in the south did not use it and had a spacer installed instead. The 2 inch exhaust manifolds are really restrictive. Used manifolds for our trucks are plentiful in the Junk Yard and the left manifold is available after market new. If you have the system apart, get the bigger manifolds and smooth them off before you reassemble the engine. The heat riser is available from Four Seasons at 972-316-8100 address is 1801 Waters ridge, Lewisville, TX 95057 PN# 122 Heat Riser. I paid 60 bucks.
William in Atlanta"

So given all that, my questions are as follows.. and keep in mind that I am not trying to be disrespectful or to pick on William or anyone else. I am just trying to validate conflicting information that I have.

William, where do you get the info on all FE's having a heat riser? My exhaust manifolds (68 390) certainly do not look as though they were designed to have one - either on the driver's side (which I understand the 352's have) or on the passenger side, (which I have seen pictures of and I'm told are for cars, not trucks). As I stated, neither of my manifolds would accept a flat gasket without leaking, as they both accept donut gaskets.
No parts store that I called (NAPA, AutoZone, Advance Auto, etc) shows a listing for these for a 68 390 -- they do show a listing for '73 on up. The info I have from Ford also indicates that the 390 did not have a heat riser until '73. I called Four Seasons, and the part number you indicated (122) is for a 73 up. They do not show a part number for a 68 390 heat riser.

My next question has to do with the 2 inch vs. 2 1/4 inch manifolds.

I measured the exhaust ports on my C8AE-H heads, they are almost 2 inches tall and about 1.5 inches wide. The ports on my exhaust manifolds are a little bigger - 2 inches tall and a tad wider than the head port. Now, you've stated that the 2 inchers are very restrictive. Is that because of the difference in port size, or because the manifold is shaped differently to allow better flow? If it's just port size, I wouldn't think there would be much benefit to the extra quarter inch of port opening. In fact, I would think the extra size would lower the velocity (speed) of the exhaust gases flowing out of the head, which I understand to be a "bad thing".

I'm really learning a lot about this stuff, thanks for your help.

Pat

 

Hey Pat, just to get you going a little bit, the 2" and 2 1/4" that William is talking about is the manifold outlet diameter, not the port sizes.

Gee, you didn't copy/paste my response.


Barry

 

Thanks Barry,

I wanted to copy everything, but I thought it was long enough as it was!

I understand that we're taking about exhaust manifold port size, maybe I didn't state it clearly. My question is, the exhaust port on the head is only so big. It can only flow so much, so fast, based on that port size. What difference does it make if it dumps into a 2 inch exhaust manifold port, or a 2 1/4 inch exhaust manifold port, or a coffee can sized port?

I've heard William say that the exhaust manifolds are restrictive. Ive heard others say that they aren't that bad. I'm trying to find out where these opinions come from. I'd really like to see some data that shows one or the other.

 

William is right. They are horribly restrictive. The problem is not the port sizes as much as the design. A header has a smooth path from the port to the collector. On a stock manifold the air leaves the head and rams right into a cast iron wall. They aren't so bad on a stock engine but absolutely forget about performance. You can make decent power through them but you will be loosing a lot also. The bigger port in the outley will help out. You have to figure you have 4 cylinders feeding into it. If it didn't help you would not have any backpressure to start with and this is not true.

 

That's what I was asking - port size or design. Thanks to you and William. You too, Barry

What is the "outley" ?

 

Hey if you don't mind me butting in again before William checks in, I just want to elaborate. The log manifolds we are talking about with the 2" and 2 1/4" outlet all have the same size inlet ports (the ones mated to the head ports).

T-birds used the 2 incher while most of the full-size cars and all pickups used the 2 1/4 incher. They do flow better, in fact they were stock on the 428PI engine rated a 360HP. On a stock or mild engine I prefer them over the headachers.

Barry

 

THE LIGHT HAS COME ON! I was missing the fact that you all have been talking about the exhaust manifold OUTLET (I just mis-typed outlet - now I know what the "outley" is ). I assumed inlet, which I measured and they happen to be 2 inches, so I thought that's the port we were talking about - the outlet on mine is 2 1/4 inches. D'oh!

 

You must be having a day like mine. That's funny.

 

Yeah, MAJOR brain-lock, but I'm ok now - relatively speaking....

 

All True! I love this site! The flat gasket bolts where the doughnut would go, then the heat riser, and then the 2 1/4 doughnut, then the exhaust pipe. I mispoke "all Fe's have a heat riser" I should have said all FE manifolds have heat riser passages. If you live in a warm climate, use a 390 thermostat, and have a warm air provision on the intake syatem you may not need the heat riser. I use a 190 thermostat, heat riser, manual choke and dual 2 1/4 inch exhaust through a 70 series Flowmaster. Shortly I will install a 2 1/4 inch equalizer tube under the oil pan. I have a fairly long commute so the engine gets nice and warm and stays that way.
William in Atlanta