Never seen an equal length turbo manifold for a KA

[RedlineRacer]

Whats up with this? All I ever see is the log style. I've been thinking about making my own equal length manifold for the KA. I've already talked to a shop about making the manifold flange and a guy I know is interested in welding it for me. I just hope his welds are strong enough.

[thx247]

Basically, it is too difficult to properly make and TUNE an equal length turbo manifold to be better than a log manifold.

[theronin]

enjoy!

boo yeah (http://www.import-autoperformance.com/Manifolds%20and%20Accessories.htm)

[andrave]

yeah iap is great, but the price is rediculous. also I've heard stuff about them cracking but I think some of that was from people that didn't have properly supported exhausts.
also I think since they added the wastegate brace it has been improved.
Anyway its a nice manifold but for the price, why?
people are hitting 400 at the wheels with a 250 jgs tools log style...

[Joel 180]

Turbos dont need equal length runners as much as N/As do to make power. Plus they are harder to design and more expensive to produce due to the limited space avaialble in the engine bay (require more mandrels).

[RedlineRacer]

omg, thats way too expensive. Are there any fitment issues whit a KA-T? I imagine there wouldn't be because there are none with the SR, but I was just thinking that the KA might be a little bigger.

[theronin]

Originally posted by RedlineRacer
omg, thats way too expensive. Are there any fitment issues whit a KA-T? I imagine there wouldn't be because there are none with the SR, but I was just thinking that the KA might be a little bigger.

well its made for the ka.

[RedlineRacer]

I don't get it, if you say log style manifolds are just as good as equal length, then why do all the top name perfomance companies make equal length manifolds? And, all the cars that I have seen that have high hp have equal length.

[THX1138]

Joel didn't exactly say that log-type manifolds were as good as equal-length, just that the difference is less with a turbo than it is NA. There will still be some improvements with equal-length mani on a turbo, they just won't be as dramatic as the improvements on an NA motor.

[gilwankel]

Because a properly designed equal length manifold will make more power and will spool quicker but who cares about that crap anyways. :)

[thx247]

There is alot of good information about this out on the internet.

But basically, the amount of knowledge required to utilize a tuned turbo manifold better than a log manifold is beyond the scope of this forum, and for that matter any other 240 forum I have seen.

Here is a brief post by a guy named Warpspeed. Read the post, and try to figure out what he is saying lol. Sometimes you just have to go with whats cheapest and what works well. We are not building race cars here.

Warpspeed-

"There are a whole lot of issues to resolve, there is no one correct solution.

On a small turbo street application where exhaust back pressure is considerably higher than boost pressure, the best approach seems to be the shortest length/minimum volume manifold that does not actually restrict flow.This is going to give best turbo response, but this is for a tractable street setup, not a max power application.

Exhaust reversion is going to always be a problem because of the very high static exhaust manifold pressure, and there is nothing you can do in the way of manifold design that is going to really help much.

Now consider a more healthy engine, with a much larger exhaust turbine, where exhaust back pressure might be about the same as boost pressure. Here there might be some gains to be had by thinking a bit more about the exhaust manifold design.

One factor to consider is exhaust cam duration and how many cylinders feed (each?) turbo.

For instance on a six cylinder engine with three cylinders feeding one turbo, the firing interval would be 240 degrees between each cylinder. If exhaust cam duration is 240 degrees or less, each exhaust valve will completely shut before another opens. In this case you can combine all three cylinders very close to the head and build a short minimum volume exhaust manifold, again for best turbo response.

The identical setup with a 290 degree duration exhaust cam will have periods where two exhaust valves are open together. One cylinder will be right at the beginning of the high pressure blow-down phase, while its neighbor will be at the sensitive valve overlap period. One cylinder will blow straight into the other.

You can fix this by using long individual runners from each port to the turbo flange. The pulse has to travel two runner lengths before it can blow into an adjacent cylinder. So above any reasonable mid range RPM, you can effectively isolate the exhaust ports.

On a big cam, big turbo engine, low RPM turbo response is not an issue, so the extra pipe volume does not hurt.

Pipe tuning on an n/a engine works by having the end of the pipe discharging into a low pressure. This creates a negative return wave that can be timed to coincide with valve overlap.

A turbo manifold terminates in a restriction, because the turbine scroll is always the most restrictive part of the whole exhaust system. So there can be no return negative wave to tune.

Most of the individual runner exhaust branches that you will see, are usually about twelve to fifteen inches long, which is sufficient to separate cylinders, but far too short for exhaust pipe tuning in the usual sense.

There may be some evidence to suggest the branches may be tuned to a harmonic frequency, as is done with intake runners, but I have never heard or read of anyone claiming to have successfully done this.

As the runners feed into a restriction, the return wave would be a positive pressure wave, so it is difficult to see how this could be tuned in any way to offer an advantage.

On a real race engine the turbo will be enormous, and the power band very limited indeed. The restriction through the turbine will be quite a bit less than boost pressure. These engines often DO use tuned full length exhaust runners two to three feet long, and it apparently can work very well.

So you really need to think through your application."

[andrave]

wow I understood all that, good reading! brought up stuff I hadn't ever even thought about before (cam duration to header length, interesting) but of course I couldn't actually apply it... but it was good readin.