I have a bw s366 with a .91a/r twin scroll hot side, the engine is a 13b turbo half bridge, I was wandering if there is a smaller frame exhaust housing I could run to get in boost faster as I don't drive the car at the top of the power band all the time. Is there any way I can get more bottom end grunt with a smaller frame housing? I found an .81a/r single scroll and it has me intrigued.

 

Not being a dick but it sounds like you should swap your whole engine package with someone with a stock port or mild extend and a gt35r sized turbo. If it is an REW motor and your ecu has the capability you can increase the bottom end VE by controlling the secondary "warm up" throttles to stay closed below about 4000rpm so it has more torque and passes more air.

 

Yeah thought of saving my money and buying a set of irons and rebuilding with a street port and smaller frame turbo. But if I can make something else work slightly better without spending thousands of more dollars then why not try.

 

will do my best as well, but no guarantee

Maybe consider the opposite; smaller turbo with bigger A/R housing?

I think the results in this link below kind of surprised a lot of people (received more discussion in a different thread). You can see the BP influence on boost pressure relative to output. Because an REW might typically be up to 2x more boost to achieve the same result, yet run out of top end rpm sooner

https://www.rx7club.com/time-slips-d...5-psi-1122867/

except consider an SXE257 1.09 A/R divided T4 as a lower cost choice for a similar result.

The other alternative is a more efficient turbo sized a bit larger like the Garrett G-series (still flying way under the radar here imo) that can kick out the flow/response with lower emap, but that’s a low-mid $2XXX change. Might as well change irons and rebuild maybe.

Because I’m thinking that stepping down to the SXE362 isn’t going to gain so much since it has the same turbine already on there now, but I suppose if you’re willing to throw some cash in a hole along with some gas and a match rather than doing the right thing it might be worth a try if the SXE257 output is too low for your taste.

That’s still better than what you’re proposing; going one A/R step down to an open scroll housing. That’s likely to get you little to nothing on the low end compared to the existing divided housing. However, if you insist on that direction then AGP Turbo offers the SXE366 with an 0.83 A/R divided T4 housing so they should be able to sell it separate. Imo that will likely do more harm than good trying to overcome all the mass of that turbo.

The 366-369SXE would be considered the “correct” turbo for a BP, since that porting change automatically shifts the entire powerband to the right side of the dyno sheet. It could be argued that the 0.91 housing is already too small as it is. I suppose you already understand that emap is effectively the equivalent of “anti-BP/PP”. Changing to an even smaller turbine housing suggests self-defeat before even pulling out your CC to order it.

That’s why I’m thinking smaller turbo, bigger A/R is the better alternative. The BP is going to allow more flow through the engine to spin up a smaller turbine wheel quickly and the larger A/R is going to compliment that without the compressor wheel loading up against boost restriction, which will avoid emap. That’s how I interpreted the result that was linked above anyway.

So if low-mid 400 whp of an SXE257 isn’t enough (they did get it up to 431 whp @ 13.5 psi later) then maybe consider the SXE362 (8376) with 1.00 A/R divided T4

good luck with whatever you decide to do.
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Thank you for the info, it makes more sense now. This is EXACTLY the answer I was looking for. I may leave the car alone with that note and build me another one more suited to being more drivable in the mid to lower range. I have too many things working against me with this current setup.

 

Stock/extend ports make LESS midrange torque than a good bridge port.

 

I ran the car for 4 years n/a with a racing beat holley and intake same everything s4 n/a rotors same port same exhaust and it felt like it had way more mid range grunt then. Now I'm using a t2 intake and obviously turbocharged, and midrange power is nowhere to be found but when the turbo spools its one hell of a ride.

 

The T2 intake manifold sucks, it clears the stock turbo and that's about it for good qualities.

 

Yes it does, I feel like it would work well with a supercharger, or a turbo setup that makes 8 psi at 2500 rpm, but other than that it is really bad. Maybe changing the intake manifold will help me out? Will a rew intake bolt to a t2 block?

 

negative ghostrider … aftermarket LIM

guess that’s what I get for assuming it was an REW

 

If someone is talking about getting into boost fast it usually means well below 13b peak torque rpm. Small turbo stuff can be well on by 3500rpm, are you legit telling me an early open late close port is making more torque at 3000rpm? That seems to go against what pretty much everyone experiences. 4500+ yeah sure but most people probably don't regard that as early boost response.

 

Nope just a ratty first gen with a t2 swap. This poor car has had so many engine/drive train combinations its getting hard to keep track. I will say as much fun as turbos are this is likely my last turbo build for this one, the heat and parts breaking is kinda not worth the "oh cool check out the turbo rotary" at car meets. Anyway who makes a LIM that is good?

 

Naturally aspirated, my half bridge Turbo II engine's torque curve started around 2000rpm, and at 3500 it was making more torque than the same engine did at peak (5500ish) when it was a street port.

It got WAY BETTER when I ditched the T2 intake manifold in favor of a S4 N/A intake manifold. Lots of epoxy was required to make it work. But the torque came on like a big-block down low and it didn't stop pulling over 8 like the T2 intake did.

This was all ten years ago or so, so the dyno plots are probably gone to the bit bucket.

This goes in line with what most people experience with half or full bridge on turbo engines, as well. The thing is, most people who do this are going for big HP so they slap a huge turbo on it to handle the limitless-feeling RPM capability. A smaller turbo, still with a decent sized hotside because these engines do not tolerate high exhaust pressure vs. intake pressure, would have crazy good midrange.

The whole reason I went half bridge is because of all the TURBO people saying what wonders it did for midrange torque. And they were right. Then in 2012 I went full bridge with a Holley manifold set up like ITBs and never looked back!

I've been driving, this past week, an '81 that I'm semi-restoring. Stock port 12A, quiet exhaust, very pleasant car to live with. But driving it has been a kind of "culture shock" since I haven't had one since 2007 or so. I'm driving it and thinking, something's wrong? I'm so used to driving around down and not needing over 2000-2200rpm with the bridge port engine.

 

can’t vouch for it in any way, but maybe this LIM with REW UIM

https://www.cxracing.com/products-by...-13b/IM-FCFD-4

only other one I’ve seen is the full cast manifold from Elite Rotary, costs way more and they don’t have the best reputation on the forum.
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Unpopular opinion but I like cx racing stuff. I have an intercooler kit from them and it seems well made for the money. Sure its not the best of the best but for a car that I don't drive everyday its good.