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sounds on the money to me. i wouldnt get your hopes up to much. any rb25 making close to 400kw on a gt35 is very stout. hell my 26 only made 376 on 25pound with a t04z...

i thought the t04z make big power on rb26's?

my rb26/30 is making 405awkw (equivalent to 445rwkw) on low mount garrett -10s @ only 23psi

Had a chat to Adam again tonight.

And he said the dump and new cooler would be the best place to start.

I asked how many cars he had tuned making 400+ with a 3 inch dump and he said none.

Not saying there are not engines out there doing this. But if he says he has not seen one then there must be a reason.

For the exhaust its a 5min test, pull the 02 sensor and fit a brass adapter and vac nipple, hook the second map sensor in to it and plot it.... bingo done.

i remember talking to rob @ rips about my exhaust which is a hks super dragger (starts @ 3.25" then goes to 3.75" at the rear).

his feedback "run it with the full exhaust then drop it at the front pipes, you will then know if your exhaust is choking any power"

^^^^ How do the above two posts address whether the dump is the issue....what you have described is usefull for determining whether you have backpressure in the exhaust....not whether you have the proper gas expansion off the turbine?

If you go back to my previous post with two excerpts I cut and posted...refer to the first one...now this guy had a 3 inch dump going to a 3.5 inch side pipe...now I doubt there would be any backpressure present in this system....yet his hp was falling over. He then fitted a 4 inch dump and 3.5 inch full street exhaust and abracabra he made more power everywhere.....and if you read his post weren't not talking massive hp figures here either.

For your convenience:

Dropped the exhaust, still with the 3 inch dump pipe tho, could run an extra 7 deg timing (up to 22) and made 450 at 24psi. Now this was ok, except when we added gas, Power would spike to 490 then as the CFM increased power would always drop back to around 450 rwhp. This was with a 3 inch dump pipe, then increasing to 3.5 inch and exiting out the side of the car. It didnt seem to matter what we did with camshaft timing or anything else for that matter power always fell over hard.

So off to the drag strip, did what we needed to do with the car...... Afterwards a new full street exhaust was made, with a 4 inch dump and a full 3.5 inch system. This thing now makes more over all horse power than before with a 3 inch dump and side pipe but now makes more horse power the harder we rev the engine. Everything here has been done with a screamer pipe, So you could imagine the added stress with CFM having it plumbed back in.

Edited by juggernaut1
...and replace the 4 inch body cat with a 5 inch body cat.

agree with that too.

juggernaut is on the right track. :( yes it's good to keep heat in the pipe to keep the energy in there and keep the gas velocity high BUT you also want to allow the gas to expand nice and quickly once it's past the turbo outlet. you need to for POWER!

^^^^ How do the above two posts address whether the dump is the issue....what you have described is usefull for determining whether you have backpressure in the exhaust....not whether you have the proper gas expansion off the turbine?

agreed i should have read the whole thread :P but depending on the type dump it can still be usefull, if it is a straight through pipe then no it is a useless test, but if it is a chamber type with the usual 3 bolt flange (and 02 sensor bung placement) it will still show up any restriction, even with the exhaust dropped. We just used this to sort a restriction in a s15 that had a dodgy china split dump, then tested the tomei and CES (tomei was the pick).

  • 2 weeks later...

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