3 or 4 bolt turbo mount

LSJM1

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Jul 12, 2007
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Nice write up now can you go into the difference between on center and tangental housings and the A/R sizes I just scored a pair of old TO4s cheap 54mm comp p trim exhaust but they have on center .96 housings on them old style bolt on downpipe flange I know I'm going to have to change them for .68s or .81s
 

norbs

doing more with less
May 25, 2001
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Back to back testing on a 70 series turbo from 3 bolt to 4 bolt produced 30-40 rhwp improvement, depending on boost levels.
 
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CTX-SLPR

Active Member
Feb 4, 2004
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If you were building scratch headers for a Turbo6 in a custom application (like I'm probably going to do eventually) which would you recommend using as the flange? I'm guessing 4 bolt is going to win due to wider selection but I could very well be wrong.

Thanks,
 

bison

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Staff member
Dec 19, 2005
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If you were building scratch headers for a Turbo6 in a custom application (like I'm probably going to do eventually) which would you recommend using as the flange? I'm guessing 4 bolt is going to win due to wider selection but I could very well be wrong.

Thanks,
If you're going to be paying for a downpipe/ext wastegate and headers go directly to the tangential 4 bolt housing.
 
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83Turbo6NCali

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Apr 13, 2011
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Curious if the guy above whith the turbo figured out what his is for ? It look's like my exact set up on my 83 T Type ? I also can not seem to find any info or pic's of how the vacumm lines run or go to on my 83 Buick T Type carb I just got this car and there some vacumm lines not hooked up & I can't seem to locate any link's to lead me in the right direction ? Maybe any 1 who has this year or has knowledge in all year turbo buick's ? I'm also looking for where I can find a replacement actuator mine is suppose to be a dual port ? & the 1 I have is a single port not factory can this work and wich 1 of the 2 port line's get's used and what happens to the other 1 sorry this is all new to me ?
 

1987T

Looking for 10's
Dec 5, 2011
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Wow! Now a question I have not seen asked here is what about the difference in flow from a .63 housing to the .83 or is .85 on the 3 bolt :confused:
Sorry if this is off topic I was just wondering as Im looking at a new BB Turbo not wanting to step up to the 4 bolt flange. Maybe it will help others as well. If I need a new post just let me know.
Thanks
 

1987T

Looking for 10's
Dec 5, 2011
321
25
28
Michigan
Wow! Now a question I have not seen asked here is what about the difference in flow from a .63 housing to the .83 or is .85 on the 3 bolt :confused:
Sorry if this is off topic I was just wondering as Im looking at a new BB Turbo not wanting to step up to the 4 bolt flange. Maybe it will help others as well. If I need a new post just let me know.
Thanks
Guess I need a new post for this one :cool:
 

GetOwnedVette

Active Member
Jun 13, 2006
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After all of our testing and our results on the dynos from 1000hp capable stage 2's around 700hp to 500hp street 109 cars there are only 2 reasons I can conclude to go 3 bolt over 4 bolt. This is of coarse in applications over 500 rwhp. If you are not at minimum in the 10s or above that power level don't bother and stay 3 bolt style.


Only 2 reasons I can conclude:
1. Money (whether it be the small price difference and additional parts you need to switch up..or cause you already have most of the parts for 3 bolt style).
2. Racing in TSM to meet rule requirements.

I can't see any advantage to being 3 bolt other than the ability on here to buy and sell used parts and those main reasons listed above.

Sorry if any of this is repeated info but a few comparisons of a few 500-700hp tunes with 60/70 trim range billet turbos.

-Back pressure of the 3 bolt guys is around 2:1 or higher at around 24-30psi....where as 4 bolt guys are floating around a much nicer 1:1 / 1.3:1.

-Now this is not directly related to 3 bolt style cause you can still put a wastegate on the header with 3 bolt setup BUT then you must weld over the wastegate hole in the exhaust housing of the turbo etc etc....usually the 4 bolt setups and vbanded dp's put the wastegate where it should have been in the first place all along...on the headers. Controlling boost with these setups is impossible with an internally gated turbo....and pretty much impossible with even an external mounted in the buick fashion. My boost creep with a Tial 38mm and a Precision 6766 was really bad....and my buddy with a 44mm gate and a GTQ70 also had no chance of eliminating creep. This prevented me from using my standalones Dial a boost functions and we had to play around with the overboost shutoff since it was set to cut at +2psi.

-Also power increases are greater with the 4 bolt style as mentioned above depending on how far you are going with boost.


After dynoing my car with the 3 bolt setup I'm simply going to make the switch to 4 bolt at some point soon. Unless you are TSM or not making tons of power 3 bolt is simply a bottleneck. At what HP and boost levels is 3 bolt a true stop? Idk......that far we haven't gone yet. I'm sure the TSM guys have it written down somewhere in their secret recipe books :p
 

Mr.Spool

Well-Known Member
Nov 6, 2006
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Back pressure of the 3 bolt guys is around 2:1 or higher at around 24-30psi....where as 4 bolt guys are floating around a much nicer 1:1 / 1.3:1.
Not necessarily there are alot of things that can effect backpressure and just cause a car is 1.1 doesn't always mean the car is faster that way.having enough exhaust gas volume comes into play with larger exhaust housings and you can slow down with the bigger ones.just some food for thought as individual combo's should be taken into consideration.the matching of the parts and tune in key.
 

horndog

Active Member
Feb 9, 2005
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900+ rwhp can be achieved on a 3 bolt that I am aware of
Yes, but at a reduced efficiency. There is always a balance on matching the turbo to your setup. Bigger isn't always better.
Maybe instead of going from a 6262 to a 71, maybe change to a 4 bolt and you will be dead nuts peak efficiency.
 
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