im posting this here by suggestion, it was originally posted in turbo tech section. the person thought i would recieve real world experience by posting this here.

i looked through the FAQ's and also did search w/o success.

i have a question concerning building an exhaust header that is fabricated to take advantage of the divided turbine housing, in my case grouping 1&3 and 2&4 since my firing order is 1432, versus building a 4-1 merge.

does the divided housing really help spool quicker using the split setup vs a merge? can you explain why if it does please?

now, if you do build an exhaust header for the divided housing do you run one huge wastegate or two, one for each half?

the follow up question to that would be, how do you determine which wastegate or wastegates to use, size wise. im going to either get a gt4088r or gt4294r, whats your suggestion.

this is for full drag race application. 2276cc, 650hp, 8500 rpm.

thank you
dean

 

From my personal experience I haven't seen any a big advantage to the split manifold and or divided housing. The only real difference was the amount of boost able to made on the 2 step, which can be minipulated by the msd anyways. We run a devided housing turbo with a 4-1 merge collector, and a single 60mm wastegate does everything we ask of it. We still do have a slight creep problem in first gear, but its still manageable. I'm in no way an exhaust, or any other kind of engineer, but this is my personal experience and is backed by testing by one of the top turbo teams in the country.

 

Weird, we've seen very significant decreases in spool time and response with a divided manifold over a non divided. Significant like 1000 rpms + difference in spool.

On a drag car that spool and response isn't important (not lifting the throttle to shift) it's probably not a big deal. On a car that will see the street, it's a huge deal.

 

Ive also seen huge gains in midrange (4-4.5k-7-7.5k rpms) from divided manifold. As much as 80-100whp @ 6-6.5k rpms (on 800+hp cars)

I think by seperating the collector and keeping it smaller it helps manitain velocity to the turbine wheel. But im no expert.

I also think for your hp goal a 35r might be better suited. that brings me to a ? that ive had for awhile. Is it worth using a divided setup for smaller turbos?

Tony,what are your thoughts?

 

I know we only tried a few different setups on our own and didn't see much difference, but I talked to Bothwell in depth and went through a bunch of their logs looking to find a big difference and didn't come up with much. I know they tested and tested trying to get the most out of their setups after getting the 66mm turbo restriction. We ended up with a 4-1 mani and a 66mm divided because thats what they ran the fastest with.

 

If their logs are from the track in a no-lift environment you wouldn't be able to draw anything that shows an initial spool. Just transient response which with such a big motor and a 66mm I'm sure it was great no matter what

 

i have seen improvements in spool time from a divided housing as well, but i have also seen better boost control with the two wastegate setup/divided housing as well. i ran a 60mm gate on a single inlet and had creep problems and a 60mm on a divided inlet and hadcreep problems. i changed to two gates and can control boost how i please now.btw- you will want 2&3 going to one side and 1&4 to the other.

 

His firing order is 1-4-3-2.

 

oh. i must have missed that. what engine?

 

nevermind

 

There was plenty of engine dyno time to try to figure things out. They tested on all 3 motor combos. 2.0 was the most reliable/ fast combo. The big motor was for special occasions but didn't last very long. Sidewall load just tore it up.
Anyways, if there were advantages to a split housing and turbo, it would be a benefit to do it on a street/ strip setup.

 

Well what i've found is tubing size is also very important.. You'll want to use as small as possible without choking the engine.. Heat and pressure (energy) are want your after..
This is what will spool your turbo.. So you don't want to give any away with oversized tubing or excessive length.

Also with rotary engines I've found that divided really helps out. The reason is because theres only 2 exhaust ports and running a divided housing means each runner is completely seperate to the turbo. This is eliminating any chance of reversion back into the engine. So your definitely getting a clean charge of air.

I would imagine the same holds true to piston engines..
If your running a 4 into 1 header with unequal lengths, some cylinders will now be reverting back into the engine and you'll have dirty combustion...

I would recommend building a divided header...