48mm Vs 50mm

[czy18e]

I am currently running a 48mm progate and since fitting the 6870 it will not hold boost at the track.

It held it on the dyno with slight creep after 6000rpm but at the track I'm hitting boost cut in first no matter how low I set the eboost.

Has anyone done the straight swap for a 50mm? Will it hold it ya reckon?

Or will I have to get a 60mm and do a cut and shut job on the exhaust manifold?

[KiwiRS4T]

Not enough information . What engine? Have you got a boost chart? What power are you making? What spring do you have in the wastegate? What kind of dump? Pics? What is your boost cut set at? What ecu?

[czy18e]

Rb25

650hp before it breaks down at 7200rpm (revs to 8000)

Boost cut is set at 32psi

4" dump front wheel exit

Ems computer

14psi spring

No boost chart.

[czy18e]

Want it to hold 30psi for 700hp (on dyno we had it set at 28 and it crept late then ignition break down at 7200)but as stated at the track I had it set 20 points lower on the eboost and it still hit 32psi as soon as it could in first gear.

60ft in 1.34. Was like a boost line was off.

[KiwiRS4T]

Try a much stronger spring first - as near as possible to target boost is better. Set your boost cut a bit higher. Does it overboost in the other gears (apart from 1st)? If you can borrow a 50mm W/G that would be worth a try but if you have to buy one I would go straight to 60mm.

[scotty nm35]

If a boost line was off it may have hit over 60psi, mine did.

Not sure about the gate you have, but Turbosmart had to re-design their spring caps to hold that boost. They made a much taller cap with springs 3 times as long, so the stiffer springs wouldn't limit the travel of the gate.

If you hit the soft limit at the track, that would cause overboosting no matter what the controller was set to.

[jet_r31]

probally no point f**king around, just get a 60mm

cheers

darren

[czy18e]

Interesting Scotty that sounds promising for the 50.

Jet I would just get the 60 but it's a manifold off job, which I will do if I have to but I'm sure ive read plenty of people having success with the 50 so just chasing feedback. So easy to just bolt the 50 on and go racing. 60 is a major for me at the moment.

Thanks for the feedback.

[jay-rod]

My mate had same problem at near 570hp at rear wheel on a rb25/30

He had a 48mm gate, had troubles with boost spikes not holding.

Swapped it out for a 60mm and fixed the problem right up.

[scotty nm35]

The gate angle must be really crappy.

[czy18e]

It is twin scroll with two pipes feeding into the single gate flange.

[Ben C34]

Problem found.

[iruvyouskyrine]

Why people have a split pulse manifold and share a gate is absolutely beyond me.

[czy18e]

Bugger.

So just never been a problem before because ball bearing Garrett not as efficient as precision or is it the size of the 6870?

It controlled boost perfectly for 9 years with the old turbo.

[czy18e]

Ok how about if I come With a possible solution.

What if I keep the 48 in its current location and weld one of these 35psi jobs to the turbine housing?

Or should I just cap off the original and weld the 48 to the turbine housing?

[Ben C34]

cap original.

[czy18e]

Copy that.

[Dose Pipe Sutututu]

more springs

[czy18e]

How would more springs do anything beneficial?

I have over boost problems.

[scotty nm35]

Over boosting isn't really an issue is it?

Gate off the housing would be the go. Make sure it flows in the direction the gasses are traveling, not backwards like that manifold.