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To shield or not to shield, thats the question...

4K views 20 replies 13 participants last post by  Manta Rallier 
#1 ·
Hello Gentlemen (& gals),

Happy new year to all!

As some might remember I gave my self a Shorty Header from OGTS as Christmas present, (and I gave my wife a pair of size 45 rubber boots), just to make Christmas eve a little more fun. As I had foreseen my wife started ranting that I spend to much money on a crappy old car, and what was she to to do with a gift that wasn't from her wish list. My reply was : "Since you always exchange what I give you for present rubber boots size 45 would be as good as any present I could come up with".

Rest of the family found my prank hysterical funny :lmao:

Anywho, the primary reason I "invested" in a Shorty Header was to get rid of the warm start problems many of us has experienced . I already got the electric fuel-pump, phenolic spacer and the heat shield, which have helped a lot, but a shorty header could be the answer to remove the last bits of warm start troubles.

Now, if I leave out the heat shield going forward I will have the space and opportunity to re-tighten the six bolts holding the manifolds to the engine block if necessary, and if I mount the heat shield...- well not so much!

So question is, does the Shorty Header reduce heat around the carb. so much compared to the original cast manifold, that the heat shield becomes unnecessary ?

Cheers.
 
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#2 ·
Compromise.

Drill access holes in the heat shield.

Part of the problem with the heat is that the engine compartment, itself, doesn't vent well.
I think it's a wise idea to add electric fans just to be able to have them help vent the engine compartment for 30 seconds after the engine is shut off.
 
#3 ·
#4 ·
That's a side draft heat shield, do you have side drafts?

After battling heat issues for decades here in humid New Jersey and trying every gimmick under the sun to combat vapor lock due to heat, I'm convinced that most of the heat comes from the oem intake manifold heating up due to it's close proximity to the exhaust and the shared bolting at the block and that heat then getting transfered to the downdraft carb via the attachment bolts and close proximity to the carb. I don't think that shielding the carb does schitt. The only thing that worked 100% was switching to the Steinmetz single side draft offset manifold. It moved the side draft twice as far away from the engine. I also did have the heat shield on the bottom of my single side draft also.
 
#7 ·
I agree that the original setup where the intake manifold is bolted directly to the cats iron exhaust manifold is the culprit for most of the warm start problems. Denmark is not the hottest place on earth but I still had the warm start problems (esp. those 10- 15 min. after a run). As stated earlier I switched from mechanic fuel pump to electric, and have both the phenolic spacer and heat shield in between my 32/36 Weber and the intake manifold...- and that combined made a huge difference. On really hot days troubles are less, but still there to some degree, which where the main reason for me to purchase the Shorty Header.

I guess the separation of the intake and exhaust manifold will make quite a difference, as the original cast iron exhaust can really generate and store heat.

So question is, does the stainless Shorty Header reduce heat so much compared to the original cast manifold, that the carb. heat shield becomes unnecessary?

I can see some benefit in being able to re-tighten the manifold to head bolts, which is not possible with the carb. heat shield on...- and I understand that shielding the carb. didn't work for you Gordo, and as I think to remember you run a "Gordo special modified cast iron Sprint Manifold"?, working somewhat similar as the Shorty Header!
 
#6 ·
#9 ·
FWIW, I have a header and heat shield and spacer and have hot start problems.
 
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#10 ·
Why doesn't anyone use a gas cooler? I made one for my hot starts, and have never had a problem since. This is what I used:https://www.summitracing.com/parts/prm-691/overview/. I had replumbed the gas line anyway to 3/8 steel line, back to front. Came through one of the holes in Radiator shroud with a rubber line to cooler, out from cooler, rubber line to carburetor. Using an electric fuel pump helps as I let the engine just about cut itself off, using a manual fuel switch. Jarrell
 
#11 ·
Cutting the fuel off is a good way to prevent boiling after shutdown. I'm going to add that until I find a better way.
 
#12 ·
While I haven’t proven anything to say what works, below are my thoughts.

First, the fuel line needs to be routed away from the engine. I’d run it up the brake support brace and then up the radiator cross frame. There is a groove at the top, I’d run stainless tubing across the top between the radiator and the cross frame. Come out on passenger side of radiator and fuel hose from there to reach carb. This should cool down the fuel a bit.

My other thought is to use ceramic coatings on the exhaust header, intake manifold, carb, and air cleaner. Make it harder for these parts to absorb and transfer heat. Ceramic coatings can do a really good job at this.
 
#13 ·
Some of the other experiments I tried:

1. Fuel line heavily insulated and run along the brake booster support to in front of the radiator wall, then to the carb via the cold air intake openings in the radiator wall. No noticable effect.

2. Trimming away the webbing on the cast iron exhaust manifold. No noticable effect.

3. 1/2"-5/8" thick phenolic spacer. Some improvement.

4. Vent the living crapp out of the hood. No rubber seals, holes and vents everywhere. Some improvement.

5. Electric fuel pumps. They help you "recover" from the problem of the gas boiling away in the carb much better, but don't stop the actual problem of the carb getting so hot that it boils the gas. I think every Opeler should use an electric fuel pump. Turn the key to Run, count to 5, your empty fuel bowl is now refilled, 3 pedal pumps, you can now engage the starter. Works marvelously.

6. Cold air intakes taken to the extreme. I've had the filter all the way up front pressing against the grill, followed by 5'-6' of duct work to the carb. Some improvement.

7. Keeping the engine fan. It is my opinion that keeping the engine fan is essential to helping cool off our hot GT engine compartments. They keep constant air circulation happening. I think it's utter madness to just use an electric fan, especially one on a thermostat that only comes on when your water temp spikes. I use both the engine and an electric fan. The electric one only comes on when the temp goes above 180*. I like the idea of electric fans that run for a while after shut down. Modern cars do this, so there must be a very effective reason to have this feature.

8. Headers and coatings. I've only actually used a Pacesetter header, but I used it for 25 years. This was the time period when I put 200K+ miles on my GT as a daily driver and the car that gave me the the most trouble with heat soak. It was a new big valve 2.0 with a Combo cam and a 32/36, plus an auto tranny. I got stuck countless times after short stops in the parking lots of convenience stores and at gas stations waiting for the carb to cool off and stop boiling my gas as I would try to restart. I think I used a mechanical pump back in those days. In recent years I've used the Sprint style cast iron manifold without the chimney. I trimmed the webbing away on one of them. That seemed to help a little, probably solely because air could flow through that area better. My present set up is a cast iron 2.4 manifold that has been jet coated. I don't think the coating does much of anything. I will soon be running Opel FI with it's freakin' huge manifold and runners. The runners are 3-4 times longer than the runners on a stock intake and the main plenum cylinder is over a foot long and 3" in diameter. It's also elevated almost 12" away from the exhaust and sits almost higher than the valve cover. The ones made for 2.4's are made almost an inch or two taller than the 2.0/2.2 ones that most of us use. Why did Opel opt to make such a huge manifold when they could have very easily made it much more compact and much lower in the engine compartment? I think they were worried about heat soak due to the inherent design deficiency of having the intake and exhaust on the same side of the engine right next to each other. And think about this: The entire FI manifold experiences almost zero fuel passing through it. The injectors are placed just 1" away from the ports in the head. That's the only area that has fuel passing through it. The entire rest of the manifold assembly has nothing but air flowing through it. Why the heck did they make it so BIG? Plenty of guys have installed individual throttle bodies on CIH's with almost no runners and no plenum. I don't recall hearing anyone with FI complaining about heat/fuel issues. Additionally, as related in previous discussions on this subject, you don't hear guys with Mantas and Kadetts complaining about carb boiling. Why? Much bigger radiators and much more spacious engine compartments.

I don't think the Shorty Headers will do a dang thing to reduce heat soak. That's not what they're for. They're so that you can use the stock headpipe and fit more compactly in a GT engine compartment. The previous types of headers had that crappy fitting 4-into-1 union at a custom headpipe union. The Shorties are 4-into-2(I think) at the standard Opel headpipe flange and location, the headpipe then merges the 2 into 1. That said, I think those Shorties are great and I would buy one in 2 seconds(gotta put down my beer first) if I didn't have the set up I currently have.


So, if you read my previous post and what I have said here, you will see why I don't think shields, wraps and coatings, fuel line rerouting, and fancy exhausts have any meaningful effect on carb boiling. What does seem to have the greatest effect is more engine compartment room(ie. engine compartment ventilation), good radiator cooling, and moving the carb as far away as possible from the exhaust.

Keep in mind that almost no one complains about heat soak, vapor lock, and carb boiling while they're driving. The problem occurs after you do a brief shut down after being at full operating temp or when stuck crawling in traffic. What's the difference? Airflow. And that air flow includes the air flowing through the carb. Air through the carb and intake naturally cools the surrounding metal.

Here's another thought: Our water pumps turn very slowly at idle, as do our engine fans. I get to experience getting stuck in traffic on a hot Summer day quite frequently. My bigger(ie. hotter) engine is encased with heat retaining chrome and has a heat retaining cast iron manifold, plus my engine compartment is congested with lots of extra junk. Parked in traffic, I get to watch my temperature gauge needle creep up into the danger zone quite often. Then I start to experience the precursors to vapor lock start to happen. The solution? Put the car in Neutral and keep the engine rev'd at 1500, instead of the 800 that the auto tranny forces it to stay at. Zooom! You can watch the temperature drop almost immediately. Need more cooling? Turn on the heater. Another 10-15% of cooling(and sweating your azz off in your car). My auto tranny is on a separate too large tranny cooler, so my auto tranny probably isn't the cause of water temp spikes. I also have a 3-core radaitor. Just reving the engine to 1500 dramatically reduces my car's engine temp. Why? I attribute it to my engine fan swirling the air, more cooling air flowing through the carb, and the water pump circulating the water through the system faster.

The above is what has worked for me while stuck in traffic. As far as boil off after shut down, yes, it still happens. But since I switched to side drafts there for a while, that problem diminished, probably due to the fuel bowls in the carbs being twice as big. I've been using electric pumps for 10 years now, so I can easily refill the fuel bowl before restarting. Just wait 5 seconds.

I'm quite intrigued about the concept of adding a fan to blow on the carb after shut down. Previous discussions have revealed that some cars with intakes/exhausts on the same side of the engine came from the factory with engine off carb cooling fans. So why can't we have carb cooling fans? Space is the big problem. Where ya gonna put it? There's not much room in that area. I've never heard of anyone doing a carb fan mod, but I'd love to hear the results from someone who has actually done it.

Auto part Engine Automotive engine part Carburetor
Red Auto part
Bumper Automotive exterior Exhaust manifold Auto part Vehicle


:veryhappy
 
#15 ·
<snip>
I'm quite intrigued about the concept of adding a fan to blow on the carb after shut down. Previous discussions have revealed that some cars with intakes/exhausts on the same side of the engine came from the factory with engine off carb cooling fans. So why can't we have carb cooling fans? Space is the big problem. Where ya gonna put it? There's not much room in that area. I've never heard of anyone doing a carb fan mod, but I'd love to hear the results from someone who has actually done it.
<snip>
:veryhappy
Fan might not blow after shutdown :)ugh: or does it?). It does blow air on downdraft carburetor:
https://www.opelgt.com/forums/after...08301-gt-cooling-down-fuel-2.html#post1400413
 

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#16 ·
I know a lot of you have problems with hot starts but for some reason I don't. After sitting for 2 or 3 weeks it usually takes me about 3, 20 second cranking intervals to get it started. Along with a lot of gas pedal pumping but when she is fully warmed up after driving for awhile, all I have to do is put the pedal to the floor and she fires right up.
 
#17 ·
Back to the original question about header or cast manifold.... My experience is that the cast iron puts less heat in the engine compartment when running. It stands to reason... the thermal resistance of a thick walled cast iron manifold is several times higher than that of a thin walled header pipe. That is going to make the cast manifold surface cooler than the header pipe when running, regardless of how long they have heat soaked.

But I agree with the point that the physical connection of the intake and cast exhaust manifold is a great heat conduction path. Cutting/grinding off the flanges of each will give some relief. And the larger thermal mass of the cast manifold will push more heat in to the engine compartment when sitting after shut off. So that is a + for the header.

IMHO, a header or manifold with a thermal wrap will do the most in that area. It breaks the radiated heat path AND raises the thermal resistance a large amount to lower the heat conduction into the engine compartment's air both running and sitting.

As for ceramic coatings.... it all depends on if it is a true thermal barrier coating or just a good looking ceramic coating. It would have to be a true TBC to cut down engine compartment heat. I do not know who does what..... and would not necessarily trust advertising claims.

A heat shield can only help by blocking one path of heat to the carb: direct radiation to the carb from other hot objects. It may or may not be a minor path for heat conduction, depending on all the other paths.

And as for FI..... the high pressure in the system is the way in which it eliminates boiling. Once the fuel pump pressurizes the fuel, which takes not more than a couple of seconds, no more boiling. And the use of a typical fuel regulator in the engine compartment, with a bypass back to the fuel tank, pushes cool fuel through the lines at all times.

An electric fuel pump running fuel to a carb does not help that, unless it is in the line from tank to an inline pressure regulator where somewhat higher pressures can reside. But that is still not quite like an FI pressure level. Some guys in V8-land have helped fuel boiling in the lines by running a higher pressure fuel to a bypass pressure regulator near the carb, or to a fuel filter right before the carb with a return port, with a return line back to the tank, to keep cool fuel flowing in the lines at all times like in an FI system.

Some of the differences in everyone's results may also be in your local fuel blending. The EPA mandates certain fuel blending characteristics and it is different in a lot of the urban and heavily traveled highway corridors. I read a reference to at least 20 different fuel blending 'formulas' around the US alone; these include re-formulated fuels (RFG)as well as limited Reid-vapor-pressure (RVP) fuels. FWIW.... Ethanol blend fuels tend to have higher volatility than non-ethanol fuels.
 
#18 · (Edited)
That is going to make the cast manifold surface cooler than the header pipe when running,regardless of how long they have heat soaked.
But the problem here is not when a GT is running, it's after the engine has been shut down and no more air is flowing through the engine bay. Heat soak is how long it takes for a material to cool down and it's directly proportional to the thickness of the material for a given heat transfer coefficient under conductive heat transfer. The reason why an exhaust manifold will take longer to heat up is the same reason why it will take longer to cool down. There is more mass to heat up, so there will be more kinetic energy stored in the object that has to dissipate. A tubular exhaust header will heat up faster but it will also cool down faster. Then when you get into radiation heat transfer, an exhaust manifold has more surface area than an exhaust header, so it will radiate more heat into the engine bay at any given moment in time. So to try and tackle the issue with hot starts, an exhaust header will solve the problem faster than an exhaust manifold and that's not even looking at the issue with the stock manifold being bolted to the intake manifold for the GT.

At least that is how I see it.

It would have to be a true TBC to cut down engine compartment heat. I do not know who does what
Swain Tech Coatings | Industrial Coatings | High Performance Racing Coatings | Technical coatings to solve problems of heat, wear, corrosion, and friction

They do all sorts of ceramic coatings... thermal barrier coatings, low friction coatings, and thermal radiating coatings with various options for the different types. I'm not connected to the company, but I do like their no-nonsense way of covering their services. Their prices are reasonable.

And the use of a typical fuel regulator in the engine compartment, with a bypass back to the fuel tank, pushes cool fuel through the lines at all times.
Most GT's use a Weber but I don't believe most are using a regulator. Weber recommends using a regulator with all their carbs, and Redline Weber sells Malpassi regulators for use with these carbs. If you look into the Malpassi carbs, they look like a regulator you'd expect to see in a classic car. There are 2 types of regulators by Malpassi, the Petrol King and the Filter King. The difference being the Filter King has a built in fuel filter. For those that are interested, the Conrero GT runs a Filter King as seen below. I believe using a low pressure regulator would help with the issue of vapor lock.
 

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#19 ·
Hey autoholic..

You are right about sitting still being the real problem.... I thought I had made that comment but I guess not. So glad you commented. The cast manifold will be cooler on and near the surface when running due to its higher thermal resistance... but the mass is certainly there after stopping to slowly push out a lot of heat.

Good deal on that link of someone who does real thermal barrier coatings. I have never dealt with it....I just wanted folks to know to look for a true TBC, and be careful... who knows what marketing claims can be made. REAL TBC's, like on jet engine impeller blades, are pretty costly to do right.

Neither of the regulators you mentioned are bypass regulators. There is a bypass regulator from Malpassi, but I do not know the actual output pressure range. Here are 2 actual bypass regulators that are suited for carbs; I would bet there are others.

https://www.holley.com/products/fue...gulators/carbureted_regulators/parts/12-803BP
https://www.speedwaymotors.com/Aeromotive-13301-Bypass-Fuel-Pressure-Regulator-3-60-PSI,40596.html

I can't readily see how a pressure regulator helps vapor lock, which is in the fuel lines. Once the pump stops, the pressure bleeds off and there is no extra pressure after that happens to help avoid boiling of the fuel in the lines. Now, if an electric pump in the back by the fuel tank somehow holds the pressure in the line that could help. However, I can't readily see that happening.
 
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