Is one better than the other.

What are the differences besides the bolt pattern?

If i have a 4 bolt and switch to a 5 bolt will i loose power?



This is a 4 bolt


this is a 5 bolt (ford style)

 

anyone?

 

The bottom housing is for an internal wastegate, where as the top one can only be used with an external wastegate. they are both good, just depends on the power and the application you want it for.

Mike

 

After doiung some research I think no turbokit for an evo can use the 4-bolt unless you get rid of ther A/C Just like b-series hondas....


The 4-bolt is known to flow more than the 5-bolt from what ive read now.

ERIK

 

The 4 bolt does flow a little better than the 5 bolt. It's stated on AGP Turbos website. ...."We do not use the decades-old OEM designed 5 bolt turbine housing due to its flow restrictions at high pressure ratios. "...

 

so does anyone run a 4-bolt hosuing on an evo?

 

Yes, basically all the bigger GT turbo kits (GT30R up) use four bolt housings--RnR, AMS, BR, etc.--if you specify the right A/R. No issues with A/C.

 

I believe rnr and ams use 5 bolt housings.....

My rnr 3076r was a 5 bolt.

 

RnR can use a 4 bolt if you want them too without removing the AC but they normally use a 5 bolt with a true .63 AR housing that performs probably just as well. Earlier alot of 5 bolt designs on the GT30s were a .48 AR and causing a severe pinch in power but most companys have figured out that the 5bolt .48 was just too small for the evo after a certian amount of power and are now using the .63AR (Non PTE housing) backside. When you purchase just be sure to specify what you want and they will get it done for you.

 

Full Race and Vishnu are the only companies using a true 4 bolt turbine housing.

 

Ya, we have used the 3" GT 4 bolt housing on several cars. It does work well, but requires more work.

 

The manifold's placement of the turbo is what will allow the usage of 4 bolt housings. HKS has been using their GT 4-bolt flanged housings and Garrett Japan non-BB 4-bolt housings on EVO's since the early 90's. The HKS, Fullrace and other AC compatible manifolds place the compressor side of the turbo closer to the transnission so there is more room for large DP's.

 

very interesting

 

The main reason for the difference in flow of the two designs is because the 5-bolt is more of an on-center design. The curvature in the inlet of on-center exhaust housing causes exhaust pulses to partially hit the exhaust before spooling the blade. As the incoming flow from the manifild bounces off of the curvature of the housing it causes a restriction in flow. With a 4-bolt housing the incoming flow of exhaust has a direct path to the exhaust blade. I will try to dig up some detailed photos or illustrations of the two designs.

 

The 4-bolt uses a symmetrical scroll/nozzle design and seems to have a larger radius compared to the 5-bolt housing. Basically, for a given A/R, the larger radius on the housing, (which is non-constant about the housing) the larger the cross sectional flow area. T3 and T4 does not necessarily designate the radius of the housing.

I've held a T4 .68 A/R and a .82 T31 housing next to each other and I think the T3 is actually bigger internally. The .63 A/R 5-bolt was tiny compared to the .82 A/R T31 housing.

Oh, but the picture of the 4-bolt you posted is not a T31 housing either. It is often referred to as the "GT 4-bolt." The standard 4-bolt (T31) has the bolts on a 3" diameter bolt circle, which means fitting a 3" downpipe requires you to "clearance" the tube for the bolts. The "GT 4-bolt" has a 3.5" bolt circle which means it can clear a 3" downpipe without any of the bolt clearance issues. The GT 4-bolt also generally has a diffuser shape cut into the outlet area to improve the aerodynamics of the outlet. That housing has a step cut in that area...

You can also get a 3" v-band on these housings... That's the only way to go in my book.

Oh, one last thing, wastegate placement. Putting the wastegate in the scroll area of the turbo like the 5-bolt hosung is a good way to create boost creep issues often times. Wastegates belong in the collector of the manifold before entering the nozzle area of the turbocharger, IMO.