Having had enough of the annoying rubbing and rattling sound that the HKS 3" downpipe made against the black cross bar under the car, I decided to kill two birds with one stone and got the downpipe wrapped with thermal wrap. The thermal wrap and clamps cost me a total of $65 and installation was another $20 (the mechanic removed the downpipe and helped me with the wrap).
The rubbing sounds are gone, and the rattling is muted. However, my butt dyno seems to detect stronger pulls on the top end, and it feels as though
After multiple runs, the car seems to pull as hard as it did on the first run. Again, this is a butt dyno observation.
Question is, am i feeling things, or is there some benefit to wrapping the downpipe with thermal wrap? Should I bother to do the same for my exhaust manifold?
The only downside so far is that the wrap touches the ACD and I am somewhat concerned about that and wondering if I should get a wrapped mallet and create a bit more clearance by knocking in the downpipe a bit more. That, and a light burning smell caused by the hot downpipe against fresh thermal wrap.
Shouldn't affect power, because the only reason to wrap the DP is to keep heat away from the t-case (or other things in that area). You do get gains from coating (or wrapping) exhaust parts on the turbo, though: manifold, hotside, and o2 housing.
Ive heard that, theoretically, keeping heat in the exhaust close to the turbo keeps velocity up, which in turn helps spool and some horsepower. I dont have any evidence to prove it, and like Clay said, coating items before the downpipe is much more beneficial. There is also help from reducing underhood temperature, but thats minimal as well.
Additionally, even if there was a slight gain from wrapping the DP, it would be much less than gains from porting and coating the manifold/hotside/o2. I did all 3 of these at once and noticed no gains. The dyno showed good power (320whp/289wtq) on 20-ish psi on 93oct and stock cams, but I couldn't feel the difference, so I wouldn't expect anyone to feel a difference from just wrapping the DP.
in my expience switching from a 3" to an HKS 2.75 DP helped reduce my knock count I think the knock sensor may have been picking up some of that metal on metal contact. Less knock your computer approves a more aggressive fuel and timing curve.
Could be that I am getting less 'knocks' from less contact between the dp and the crossbar. Anyway, since I have quite a bit of thermal wrap left over, should I bother to wrap the manifold? is it a lot of effort to remove the manifold? It would probably just take me half an hour to wrap the manifold, but if it will take hours to remove the manifold and get it back on, then I won't bother.
Could be that I am getting less 'knocks' from less contact between the dp and the crossbar. Anyway, since I have quite a bit of thermal wrap left over, should I bother to wrap the manifold? is it a lot of effort to remove the manifold? It would probably just take me half an hour to wrap the manifold, but if it will take hours to remove the manifold and get it back on, then I won't bother.
This is exactly what I was going to suggest. Do any logging of knock counts before and after?
If you pull the manifold I wouldn't bother replacing it unless you were putting a ported & coated version of it back on. In othe words, unless you're bored or putting the better piece in its place leave it alone.
Just my opinion of course.
Could be that I am getting less 'knocks' from less contact between the dp and the crossbar. Anyway, since I have quite a bit of thermal wrap left over, should I bother to wrap the manifold? is it a lot of effort to remove the manifold? It would probably just take me half an hour to wrap the manifold, but if it will take hours to remove the manifold and get it back on, then I won't bother.
If you were getting false knock from the rattling, and the heat wrap has cured that problem then your seat of the pants performance gain is probably real... very interesting.
The manifold is a pain in the butt to remove if you are just going to heat wrap it I would not bother. If you can get it ported while it is off the car, and then heat wrap it then go for it.
Keith
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EVO 11.53 @ 123.37, Black WRX Wagon 13.62 @ 99.24
Also, if your wrap and pipe are still rubbing against the ACD don't be surprised if over time it rubs it back down to metal/metal. Depending on how thick the wrap is in that contact area of course.
Keith, porting is practically a dark art in this country. Not likely I can get it done, so I'll leave it well alone then.
mdog, it will probably rub down eventually, but I did make sure to set those areas to 'extra thick' wrapping.
I must say, though, that the car feels much quieter to drive when cruising at 3000 rpm to 3500 rpm. Less boomy, but I can still hear some deep thrumm, which probably means that more clearance may be needed. Looks like the mallet may be inevitable after all.
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