| Author | Message | ||
     Vsingle |
I have noticed that the intake manifold temperature varies quite a lot. At highway speed, it's only warm to the touch. But after idling a while in traffic, it gets really hot. This doesn't seem good. Some of the heat during idling gets transferred to the boot, which might explain some of the short-service life of the OEM boot. Has anyone ever tried a gasket between the manifold and head to provide some insulation against the heat transfer? | ||
| Gearheaderiko |
Actually the boot doesn't have a short service life and it doesn't have as much to do with the heat cycles when running. The lean condition that many Blasts run causing the backfire splits the boot (though I've never had one split). Many bikes use a rubber boot. The big problem with the Blast (and it might be compounded by the use of the CV carb which only opens the throttle slide with vacuum) is that when it backfires the pressure only has one place to go-back down the single manifold and one carb (a carb that is closed when the backfire occurs). In a twin, the backfire pressure can be lessened by going into the other branch of the intake manifold system. Eliminate the stock air box and you eliminate the carb support which does a lot to protect the boot. I also think that people who live with 4 seasons tend to suffer more with boot failure because the cycle of the seasons seems to be more damaging to rubber than running heat cycles, causing it to harden and become less flexible. The boot is not the huge weak link people make it out to be, compounded by the availability of a "SuperBoot" and people running without the stock air box and possibly an overweight air cleaner. Given the aging of shelved stock replacement boots, the available boots are bound to get harder with time. | ||
| Vsingle |
Most materials on earth show reduction in ultimate tensile strength as their temperature goes up. Just sayin. Backfires through the carb on my bike appear to happen most frequently on hot starts. As soon as the bike is shut off, cooling airflow through the manifold ceases, and heat from the head begins transferring into the manifold. The heat transfer is always taking place, but without the cool intake air to carry it away, manifold temperature goes up. Which leads to a thought on performance: the cooler the intake air is, the better in terms of compression ratio and oxygen content. So, again, perhaps an insulating gasket between head and manifold might be worth investigating. I am interested in your points on carb back-fires. Very true that there is no where for the shockwave to go except back through the carb. Perhaps a relief valve on the manifold would make sense for single cylinder engines? A one way flapper or reed valve to provide an exit for the expanding gasses? | ||
| Gearheaderiko |
True, but the best would be to eliminate the cause of backfires! I may have missed the word "some" in your post. What you say about heat transfer is true and gaskets and heat insulators (but they might not be called that) are available (but certainly not under a "Blast" application).. Is there a need for such insulation given a general application? Will it really make a practical difference? The factory used an O ring instead of a gasket - why? Or perhaps a different manifold? Your suggestion poses a few questions, the big question is will it make a real world difference? What is the problem you're trying to solve-heat transfer or boot longevity and are they proportionately relatable -if you solve heat transfer, what will it's relative impact be on longevity. | ||
| Gearheaderiko |
Probably too lean on hot starts. Blasts are known to have a warm or hot start issue. I don't remember exactly how it's solved, but I'm thinking it disappears when the jetting is rich ended up. | ||
| Vsingle |
To clarify, the problem I have identified is temperature variability of the intake manifold during normal engine operation. The purpose of my post was to inquire from this community if this issue has been noticed or worked on previously. I did perform a search prior to posting. Found lots of posts on boots, not anything on intake gaskets. I don't know why an o-ring was used in the design. They are cheap, and seal well against machined surfaces, but a groove must be machined to use them. Will uniform intake temperatures provide any real-world advantage? I don't know. My intuition tells me it might. However, as with many engine modifications, it's not any one single thing that makes a noticeable difference; it is usually the sum total of a lot of little improvements that yield a noticeable difference in performance. It's quite likely the first guy that attempted to smooth out his intake ports faced similar questions. Fortunately, he tried it anyway. | ||
| Ezblast |
Easy enough to solve - tune your carb so your af is similar across the board - no biggie - have at it - I've done it, so have others - use an af gauge - wide band is the best. EZ | ||
| Vsingle |
What is an AF gauge ? | ||
| Ezblast |
AirFuel ratio gauge - fi bikes use the sensor with a preset map to keep the af close to same across the board giving more consistent performance and even engine temp., you can do the same in reverse with an AF gauge and carb knowledge. EZ | ||
| Vsingle |
EZ - With all due respect, I'm not sure you're getting what I'm saying. The manifold is absorbing heat from the head, which then warms the intake air on it's way to the combustion chamber. The cooler the intake charge, the better. What's up for debate is the idea of insulating the manifold from the head With a gasket to help keep the intake air cooler. | ||
| Ezblast |
At idle/low rpm - bike is ultra lean - thus more heat, compounded with no wind for cooling, at higher speed at least cooler from air movement. Totally know where your coming from. You could try wrapping the manifold, but that heat is directly from the intake valve of the head. A richer charge is a much cooler burn - if your af was 13.5 across the board - you would see a significant temp. drop. EZ |
