Intake Manifold Thermal Reduction

Discussion in 'Discussion Forum' started by Dr.Jeff, Dec 1, 2019.

  1. Dr.Jeff

    Dr.Jeff True Classic

    Location:
    Sin City
    The topic of reducing intake air/fuel temperatures has been well documented, both for performance gains and preventing vapor lock. If you need justification, just think about the cooling fans Fiat added to the carb and FI intakes. And there are many great examples of phenolic spacer/insulators added under X1/9 carbs (for stock and performance setups). But in the same way that a insulator spacer can be added under a carburetor to reduce the amount of heat transmitted to it, the fuel injection intake manifold itself can be insulated from the head with a similar spacer. This seems to be gaining popularity with VW's, Miata's, Japanese cars, and many others. Several companies are making custom cut phenolic insulators (typically around a quarter inch thick) to install inbetween the head and the intake manifold. Here is a little article on it:
    http://www.autospeed.com/cms/article.html?&title=Cool-Stuff-Manifold-Insulators&A=110474

    And here are some examples:
    Manifold_Insulator_MI635.jpg 90ec0b6a-ddd5-4321-966f-8e6fdd0cf88b-800.jpg images (1).jpg images.jpg PC080100__41554.1399700457.1280.1280.jpg

    I'm looking at making phenolic spacers for the X1/9 fuel injection manifold. But there are at least three possible approaches (that I can think of) with it's counter-flow head design:

    1) Due to the shared gaskets and mounting studs for the intake and exhaust manifolds, the insulator could go between both manifolds and basically duplicate the shape of the manifolds' gaskets. This might(?) provide an additional benefit by separating the exhaust manifold from the hot head, therefore reducing the heat that rises up from the exhaust manifold to the intake plenum? Not sure exactly what the outcome would be. But it certainly simplifies the mounting arrangement because both manifolds will be raised the same distance from the head. So with longer mounting studs everything will install normally (just need two sets of gaskets). However I'm not certain how the phenolic material will hold up under a exhaust manifold. I did some lab testing of the material and found it will burn (as in actually catch fire) if it gets hots enough. But that was at an extremely high temp (I did not record the actual temperature when this happens, I'd estimate it was over 2000* F). The testing did show it to be strong enough (physically and chemically) to stand up to the weight and load of a exhaust manifold sitting on it.

    2) The insulator could be installed under just the intake manifold but not the exhaust manifold. This puts the two manifolds at different mounting heights so some metal spacers would be needed over the exhaust manifold's shared mounting tabs (to bring them up to the same height as the intake manifold). That is common for installing tubular headers, so easy to do. It will avoid any issues with the higher heat levels of the exhaust on the phenolic material. And the entire intake manifold and injector bodies will be insulated from the head. A extra set of gaskets will need to be cut and the intake portion used on the spacer. One potential issue might be with the different mounting heights for the manifolds; it may make getting a good seal for them more difficult.

    3) Instead of installing the insulator at the head, it can be placed between the lower runners and the upper plenum halves of the intake manifold. This would be easier as far as mounting the manifolds and spacers go. And might be less prone to leaks. Naturally the biggest drawback is it only insulates the upper half of the intake. So the runners and injectors will still be hot, reducing the benefit. Another lesser issue is the mounts for the injector rails will need to be adjusted (where they attach to the plenum) to account for the added space in the middle of things. This approach has being taken for some other engines due to the complexity of their manifold:
    Vc4arjp.png

    All of these approaches will require an adjustment to the throttle linkage due to the manifold being slightly further away. But that is easy to correct. Things like wire harnesses and fuel lines will flex to accommodate it. Until it is mocked up I won't know if other adaptations are necessary. I think I'm leaning toward the second approach (between the head and intake manifold only). Any ideas on that?

    I won't address the overall trade-off of 'benefit vs effort', that is up to each person. And as to comments like "it doesn't need it", or "why modify the stock system", or "you are over thinking it", or any other judgemental remarks - :p.

    But I do appreciate constructive comments on the project. :)
     
  2. ghostdancing

    ghostdancing True Classic

    Location:
    italy
    under the carburetor there is yet a bakelite spacer in the OEM setup..also the intake manifold itself has cooling water circulating inside (so the air\gas flow must be heated, not cooled?)..

    regarding the vacuum lock: on my car, restarting when hot can require long cranking (plus gas pedal floored) or be instantaneous (no gas pedal action required) apparently randomly..really cannot figure why
     
  3. lookforjoe

    lookforjoe True Classic

    Under just the Plenum makes more sense. The 8V setup is just so shitty in terms of heat management, anything you can do to mitigate the heat soak/transfer has to be worth trying.

    Have you also made/tested heat shields for the exhaust header/manifold? That definitely helped on my setup.
     
  4. Dr.Jeff

    Dr.Jeff True Classic

    Location:
    Sin City
    That is to heat the manifold. If you are in a very cold climate there is a possibility of the air/fuel mist actually 'freezing' to the walls of the intake manifold if it is too cold. Also there are emissions reasons for heating the intake. But for the most part performance is improved with a colder intake charge (air/fuel). So a very common mod is to plug the coolant passages to the intake manifold and reduce as much heat as possible in and around the entire intake system. This is the logic behind the "cold air intake" products (although many of them are poorly designed and actually allow hot air to enter).
     
  5. I plugged my manifold water passages but I've often wondered whether or not the water would actually cool the intake manifold once the engine warms up. It gets pretty hot next to the exhaust ports.
     
  6. ghostdancing

    ghostdancing True Classic

    Location:
    italy
    well here is never below 0 °C (better say rarely..) so i can plug water passage in the manifold and gain some free HPs?
     
  7. Dr.Jeff

    Dr.Jeff True Classic

    Location:
    Sin City
    I'm curious what your thoughts are behind this? More in terms of ease of design/installation, or more in terms of function, or ??? My first impression was the same as yours (between the plenum and the runners), mostly because it is easier to do. But the more I think about it, I'm inclined to put it between the head and manifold; despite requiring more fabrication I think it will be much more effective. For one thing I do not run the stock injector cooling fan, so keeping the injectors cooler would be a big plus - which having the insulator at the head will do (not so at the plenum). Plus the runners are located directly next to the exhaust manifold (actually indirect contact where they share mounting studs), so they will get the greatest amount of heat transfer. Insulating them from the head will certainly help. But what are your thoughts?

    I totally agree about counterflow head designs. I deal with the same issue on my early water cooled VW's. That crowd has been doing intake manifold insulator spacers for quite awhile, with custom cut ones available. They mount them between the head and intake manifold, but those engines do not share mounting between the intake and exhaust manifolds, so less complication there.

    As for heat shields in general, yes I will make several of them from an assortment of materials (depending on the location). The heat shields will be particularly helpful on the turbo engine. The intake manifold insulator may introduce boost leakage issues on that engine, but I intend to try it and see. Otherwise the intake insulators will be very helpful on the other project X (with a slightly modified N/A engine).
     
  8. Dr.Jeff

    Dr.Jeff True Classic

    Location:
    Sin City
    I don't recall if anyone here has measured it on the Fiat SOHC specifically, but there have been numerous tests for many other engines that show the coolant temp is significantly higher than the intake manifold temp. That includes counterflow engines very similar to ours, so I have no doubt it's the same.


    The performance improvement won't be huge, but yes it does help. Especially if you are experiencing vapor lock (which it sounds like you are). When the engine is cold, the heated intake manifold helps to shorten the warm up period. That is why there is a emissions improvement, less time with the choke on. But once it warms up it is a disadvantage. So like everything there is some trade-off. Most race engine designers go to great lengths to make the intake air/fuel charge as cold as possible. I think for a street use situation it comes down to the local climate, your intended goals for the vehicle (faster warm up or improved efficiency), and how you view keeping things stock vs improved. [:D that last part might stir things up a little]
     
  9. carl

    carl True Classic

    Location:
    Virginia
    It was my assumption that the coolant passages are to heat up the carb not cool it.
     
  10. lookforjoe

    lookforjoe True Classic

    I've used phenolic spacers on Volvo intakes - those were already cross-flow heads, so less dramatic a heat soak as a our old 8v setup. The problem it seems is more packaging. I would agree that pushing the runners out would make more of a difference to direct heat transfer at the head, however the runners are still right next to the exhaust header, so I still think heat sheilds are more practical in this case. Moving the (stock) injectors further out is also going to mess with the spray pattern (such as it is).

    The last version I made worked very well.

    [​IMG]
     
    Peter Cecil likes this.
  11. Dr.Jeff

    Dr.Jeff True Classic

    Location:
    Sin City
    Thanks for the input. I considered the injector spray pattern, however the insulator isn't that thick and the scalloped opening in the manifold/head is big enough (I actually opened up the scallops a bit when I was porting everything) that I don't think it will have much effect. At least not with these injectors and the spray pattern they have. But I agree it would still have some effect. Just not sure how the trade off between that and the reduced heat levels works out. Keeping the injectors themselves cooler would be a plus.

    As I mentioned, heat shields are planned with or without manifold insulators. So that really isn't part of my equation on where to position the insulator. I view them as two separate items, although they have a similar goal. In my opinion this is one situation where more is better - in terms of more heat reduction. Especially for the turbo engine.

    I haven't decided which way I'll go yet for the insulators location. I already have the phenolic material and I will make them, but it will be awhile before I get to that part of assembly so no hurry.
     
  12. gene cooley

    gene cooley Autocrosser

    Location:
    Henrico, Va
    Not sure if anyone can find anything useful here but I went back to a datalog we recorded on the 600 on 9/8 and looked up some temps and added some basic info on the car.

    Manifold is plastic, dry, (no coolant in manifold), car is mid engined with non-vented covers over engine.
    Radiator is behind the engine/trans.

    Air temp was 88F.

    Water temp was 194F.

    Intake air temp at air filter varied from 96 to 101F. Air filter is on throttle body.

    Intake air temp at highest RPM (6600) on this run was 98F and when the engine is running the manifold runners don't seem to heat up over intake air temp. That's something that I can get a reading on.

    Again, not sure if any of it is useful but it's what I have available at the moment.
     
    lookforjoe and Dr.Jeff like this.
  13. gene cooley

    gene cooley Autocrosser

    Location:
    Henrico, Va
    Some Exaust temps:
    "Normal" running -- WOT, RPM varies: mostly
    in the 500F range, 800F to 1000 not unusual.

    BUT, when you hit the limiter at 7200 and still at full throttle the AFR goes to 22 there is a period for about 0.2 seconds where the temp hits 1600F. I don't like that.

    Also;
    We killed the 02 sensor on the 3rd of 10 runs on 11/17 so we didn't get much datalogging.
    We could still read engine temps.
    The air temp was 45F. We were not hot lapping but runs were closer together than on 9/8.
    Engine temp hit 210 and at that point IAT was 97F. At 195F the IAT was only as low as 80F. I was kind of surprised that IAT was that high with the 45F ambient.
     
    AKimball92 likes this.
  14. Dr.Jeff

    Dr.Jeff True Classic

    Location:
    Sin City
    Were the ambient temps you mentioned the general surrounding air temp or the air temp within the engine bay? Because it looks like the engine temp got pretty high (210) so the engine bay temp would have been high, and therefore the IAT high.

    I'm surprised the exhaust temps aren't higher overall (aside from the 1600 reading). 500-800 seems good to me, but I have no idea how your engine compares to any I know.
     
  15. gene cooley

    gene cooley Autocrosser

    Location:
    Henrico, Va
    The ambient temps were the outside temps for each run day. 88F in early September, 45F on the 17 of November. The intake temps were also the engine bay temps at the front of the engine about 3" above the throttle body in the top of the air cleaner during the run. What I am missing is the actual temp of the intake runners, I don't have readings other than the one at the air cleaner.
    The coolant temps for 11/17 were high because we were running about 5 minutes between runs.
    The engine is a mid mounted 2.2 DOHC 4 valve Ecotec. Compression is near 14:1 running on 110 leaded VP or Sunoco. (That's what kills the O2 sensor.) We have a Geo Metro radiator with a 10" fan at the rear corner of the car. Maybe 230hp at the crank. The 1000F is "occasional", the 1600F seems to happen whenever the rev limiter hits.
    If it helps I could use the gun and take some temp readings around the engine. I would like to have the intake runner temps in any case.
     
  16. Dr.Jeff

    Dr.Jeff True Classic

    Location:
    Sin City
    Maybe you could get the temp sensor probe inside the intake manifold just before the butterfly. That should be more representative of the intake temp.
    I'm sure every vehicle will have very different data depending on many variables.
     
  17. gene cooley

    gene cooley Autocrosser

    Location:
    Henrico, Va
    That moves it about 6". I don't think there will be any difference, but, as soon as I get the laser thermometer some new batteries I'll do some checking of temps. I might find a usable port in the plenum before the runners.
    The entire manifold is plastic, so what I have is a manifold made of similar material to what you are proposing for your spacer.
    I can also do some temp checks of the manifold in the G6. It's the same one as the 600 manifold.
    Tomorrow I hope......
     
  18. Dr.Jeff

    Dr.Jeff True Classic

    Location:
    Sin City
    Sorry I must have misunderstood. I thought the earlier temps were taken in the air filter area, not in the actual manifold.



    I don't know how it would compare, but all data is good for reference. It will be awhile before any of my engines are reassembled and fired up, so I won't be able to offer test results for some time. For now my decision is primarily which location on my engine I want to mount the insulators; at the head interface or between the runners and the plenum.
     
  19. gene cooley

    gene cooley Autocrosser

    Location:
    Henrico, Va
     
    Last edited: Dec 3, 2019
  20. Dr.Jeff

    Dr.Jeff True Classic

    Location:
    Sin City
    O.k., then I think you might see a significant difference in temps between that point (air filter lid) and the intake manifold in general, with the manifold being hotter. I don't know if between the throttle body and the runners there is as much difference, for a cross flow head (I think that's what you have). However with a counterflow head (X1/9) there will be a big difference in temp due to the runners being right over the exhaust manifold, as Huss siad. To me that is all the more reason to add the insulator spacers at the head rather than between the runners and plenum; try and reduce the runners' temp as much as possible by insulating them from the head AND by adding a heat shield between it and the exhaust. But as you noted, your plastic intake manifold may be a much better insulator and therefore the runners could be much hotter than the throttle body.
     

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