Fabspeed vs Rarelyl8 Headers on Boost Creep

[MZ3 SBC]

My car- 79 930 with a Dawe built 3.4 running stock WG / Fabspeed Long Neck, Fabspeed Headers, Fabspeed Dual outlet exhaust and a custom K27 - euro fuel heads, Bosch Twin Plug and a few other goodies.

My buddies car is an 88 930 running a set of RarelyL8 headers and Outlaw pipe, Tial WG with stock boost spring and a K27 7200 ( he swapped out of Fabspeed Headers and stock WG with .9)

This comparison has nothing to do with power gain wars or 1/4 mile times...... but the efficiency of Fabspeed unequal length headers vs the Rarelyl8 equal length.

My buddy is a bit of a part swapper on his journey to the ultimate sounding 930. He is finally happy.....but here is the issue...…

When he had the Fabspeed headers and stock WG with .9 spring he over boosted and the boost pressure sensor shut down fuel pumps. He put the .8 spring back and still found boost creep to 1 bar on factory tach gauge.

He put tial on and still had boost creep.

He switched to Rarelyl8 headers and says boost is steady at .8 on the factory gauge.
__________________________________________________ ___________________

Now I have the Fabspeed / Stock WG with .8 and on occassion get .9 to 1 bar on my factory gauge...but never shut down pumps.

My buddy is convinced that the equal tube length design of the Rarelyl8 headers and WG feeder pipe does not produce an over boost situation based on the flow characteristics of the RL8 design.

I think that is non sense. I dont find any specific threads about FB headers causing over boost because the unequal flow signal to WG.....

I think he may have had a pinched boost line to WG / sticky WG or leaky WG shaft....or perhaps his set up produces more flow than the stock SIZE WG can handle ....

ANybody know anything about FB headers being a bad design....?? I think they are both excellent products. And I have to agree the Rarelyl8 and Outlaw pipe is the best sounding 930 around.....

_ I also explained that the factory tach boost gauge is probably not very accurate. I will be in stalling a VDO tell tale this week...be interesting to compare the 2.

[RarlyL8]

The severity of overboost depends on many things such as how close your boost spring rating is to the overboost cut-out, how sensitive your overboost switch is, and the flow characteristics of your entire exhaust (and turbo) system.
The difference in design is FS and most others us a single "elephant nose" waste gate pipe that exits at a 90° angle. Flow has a difficult time making a 90° turn as RPM goes up and velocity increases. This reduced waste gated exhaust volume leads to overboost. I specifically designed my system to correct this. The waste gate is fed by both banks at a much gentler angle insuring that the flow is not interrupted as RPM and velocity increase.

[jwasbury]

My own observation is the exhaust system and particularly the efficiency of the wastegate circuit has a massive effect on max boost, all else being equal.

I had a TIAL wastegate installed on my '79 with a .8 Bar spring. With the original factory exchangers and crossover pipe, I was seeing .8 bar max boost.

When I changed the entire exhaust over to the RarlyL8/SSI system, with the exact same wastegate I would max out at .6 Bar. The only possible explanation is a more efficient wastegate circuit. I added a manual boost controller to get back to 0.8 Bar max pressure.

[RarlyL8]

Here are pictures of both designs to compare.

[993Speedster]

It's pretty much a known fact that you DON'T make the wastegate path a 90* turn from the flow of exhaust; makes it a very hard path to take. You want a smooth "highway off-ramp" style exit path for the wastegated gasses. The rarlyl8 ones also take a signal from each scroll which probably helps too. Typically poor wastegate designs won't rear their ugly head in a high boost application; it's the low-boost spring that requires a lot of gas to be bypassed and the poor wastegate placement doesn't allow it so as the RPM's and airflow rises, the gate simply can't bypass enough air-mass at such a low pressure and creeps up.

[Tippy]

If I'm understanding you correctly, yes, boost creep is a very real issue on these old header designs.

My car always runs much lower spring pressures vs actual boost pressure seen in the intake.

The 'elephant trunk' WG circuit is very susceptible to creating boost creep as the sharp bends don't flow well.

[1979-930]

RarlyL8 headers with boost creep fix..




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[MZ3 SBC]

This is all great info...most of which I have read on the website...and certainly I don't dispute that the information and imperical data experienced by everyone. I have the Fabspeed on the car and Jacob can attest I am no stranger to pedal. My question is about a SPECIFIC COMPARISON between the Fabspeed designed west gate pipe and the RarelyL8....which I concur is beautiful craftmanship / better metal / etc etc.....AS I look at the headers under my car the WH coming off the turbo mounting connection seems to be pretty good.

Has anyone flow tested these products?

I am all for a kumbaya for Brians products. I agree once again in the high caliber of his products support and education work for CIS afflicted people …...but why cant I see there being threads complaining about Fabspeed 930 header design...and it would be so easy for them to correct this issue at their facility......I believe an inefficient WG design / operation coul be worse than the pipe off the headers....at least as far as my Fabspeed.

I also don't mind getting an extra .1-.2 bar of creep since my engine is built to support more than the .8 I am running. I appreciate everyone reading.....and especially contributing. Wonder where Fabspeed is on this.....Cheers to Brian for supporting his product

[Mocker]

Originally Posted by MZ3 SBC

Wonder where Fabspeed is on this.....

Well, that's the question, isn't it? Have you asked them?

[MZ3 SBC]

Originally Posted by Mocker

Well, that's the question, isn't it? Have you asked them?

I hope I just did.... I even asked the sales guy I dealt with ...so far crickets. Hopefully they can provide some additional insights.

I had a set of SSI headers and prior to seeing the RL8 headers my buddy installed on his 88....I though the FBSD were a huge step in the right direction.

I'll be ordering a Tial and .9 from Brian this week....and tempted to get an outlaw with GT3 tips.....

[RarlyL8]

…...but why cant I see there being threads complaining about Fabspeed 930 header design...and it would be so easy for them to correct this issue at their facility......

I can answer that, and it's the reason I designed the waste gate path the way I did on my headers. All the short tube headers on the market use the same design because it is cheap. Look on the internet, you can't tell the difference in most of them as they all come from the same place. They know about boost creep. Their solution? Use a smaller boost spring. It's so common that TiAL even mentions it on their website.
That's not the end of the story. When I was testing my system I purchased a set of short tube headers to compare. My mule engine was a stock 300hp Euro. Back to back I was seeing very similar HP increases, then I looked at the boost data. The OEM J-pipe system was holding 0.8bar, my tuned headers were holding 0.8bar, the elephant nose short tube headers were creeping past 0.9 bar by redline. So my headers were pulling the same power at a lower boost level.

[MZ3 SBC]

Originally Posted by RarlyL8

I can answer that, and it's the reason I designed the waste gate path the way I did on my headers.....
That's not the end of the story. When I was testing my system I purchased a set of short tube headers to compare. .

Well- I am going to leave this here and write that I am convinced by all the feedback from you guys the improvements in design make a big difference. It makes sense to me....If I was in the market for headers at this time I would spend the extra money knowing what my and other experiences have been with boost creep. And true my SSI headers seem very similar to the fabspeed except for not having heater boxes and a flimsy connection between the main headers and the WG pipe.

I been away from Pelican too long.

follow me on IG @outlaw3.4

Maybe I stick with the .8 spring in a ne TIAL

[Pat RUFBTR]

My Fabspeed modified at wastegate, 30° exit angle at the base of the T3 and 60mm tube diameter.

[willtel]

I learned a decent amount about boost creep and what causes it from watching these guys dyno tune this turbo Honda. They eventually solved their issues by welding the wastegate exit to the turbine housing and working out issues with the wasetgate signal and boost controller plumbing. I thought it was interesting.

https://www.youtube.com/watch?v=LLxSviGzYSk

In this video they retest with the new wastegate plumbing and get the numbers they were hoping for with solid electronic boost control.

https://www.youtube.com/watch?v=2MBxWkhOsXE

[K24madness]

Well designed wastegate integration Brian!

It’s difficult for most to appreciate all the little design elements in a well made system. Equally poorly designed ones attempt to seduce you with polished tubes.

This may better explain proper wastegate integration.

[RarlyL8]

Thank you!
When I first got into the turbo cars I read all I could get my hands on from Corky Bell and the likes. Trying different things with a hobby car you gain a lot of experience with what fits and what doesn't, what works and what doesn't. The crappy design of all those short tube headers puzzled me but I understood why they did it. The design was cheap and anything you replaced the stock 930 exchangers with was a huge improvement. If you're looking for max margins that's the way to go. Not so much if you are after a true performance system built to last.

[993Speedster]

I'm a huge fan of the wastegates that come right off the turbine housing... this is probably the ideal location all things considered. It's right in the highest pressure/velocity with a smooth diverging path. Been wanting to try this but the thought of trying to hole-saw through a cast iron exhaust housing sounds tiring lol.

[lite75]

Rock steady control after twin wastegate modifications.

[Tippy]

Originally Posted by 993Speedster

I'm a huge fan of the wastegates that come right off the turbine housing... this is probably the ideal location all things considered. It's right in the highest pressure/velocity with a smooth diverging path. Been wanting to try this but the thought of trying to hole-saw through a cast iron exhaust housing sounds tiring lol.

Seen it a million times. I'd imagine it doesn't get any better than that, but how long with the WG last at those temps?

[K24madness]

Originally Posted by lite75

Rock steady control after twin wastegate modifications.

Looks great!

Given the packaging problems of the 930 this is another great solution!

While I am a big fan of twin scroll single turbos it seems twin turbos layout better with the flat 6.