4age autocross: turbo vs supercharger

Aftermarket engine management can make a big difference to things like throttle response when compared with “vintage” stock parts. At these specific output levels, I’d want knock reaction capability. 

In reply to Keith Tanner :

Ill be going megasquirt. The stock ecu is not very good. It’s safe but very rich under boost.

If you carefully choose the turbo size, and preferably use a twin scroll turbo, you can minimize lag.

The LNF engines use a Borg Warner K04 unit and the torque has to be artificially limited in first gear by the program as it hits 200 ft-lbs at 1500 rpm.  If you want top end power, the turbo choice for that will affect low down torque, but for autocross, you'd want to stick with the lower peak power with the better torque production curve.  The flat torque curve on the LNF is due to the program limiting maximum torque for longevity. There is a factory reprogram that gives 340 Tq instead of the stock 260 Tq.  They still limit in first gear, though, for longevity.

In reply to wspohn :

That curve is nuts! Seems like it drives a lot like a supercharged car

In reply to Fitzauto :

twinscroll is a wonderful thing. 

Are those turbos only on Ecotecs? Becuase I have been looking for a great twin-scroll for my future 7A build and the only one I could think of were from Mitsubishi.

In reply to GIRTHQUAKE :

The one I posted is off of a 2.3EB. the later 2.0EB and whiteblock Volvo turbos are all twinscrolls as well. I believe the mini turbos are twinscrolls as well. Fabricating a manifold for them , as most have a properitary flange, is the headache. 

Fitzauto said:

In reply to wspohn :

That curve is nuts! Seems like it drives a lot like a supercharged car

The plot for my 135i is similar. Tons of tq and midrange from below 2k and carries it up to 5500ish, you can rev it out to 7k, but it runs out of breath a bit on the stock tune.

captdownshift said:

In reply to GIRTHQUAKE :

The one I posted is off of a 2.3EB. the later 2.0EB and whiteblock Volvo turbos are all twinscrolls as well. I believe the mini turbos are twinscrolls as well. Fabricating a manifold for them , as most have a properitary flange, is the headache. 

Ooh, that could fit the bill! Do you know any more than just the wikipedia page? Because right now, it sounds like I could keep the turbo and flange, and maybe weld it to the 4A-GE exhaust side.

In reply to GIRTHQUAKE :

Building a turbo 4a as well?

In reply to Fitzauto :

Yep! My running plan is the full monty; 7A-FE block and crank, aftermarket rods and pistons, cleaned up head from Oldskewltoy... I think if I wait for good deals and soak up enough from some of the group members I can have it together with little fuss and ~250 wheel HP.

In reply to GIRTHQUAKE :

you'd definitely need a custom manifold for a twin scroll, the EB flange would be about the biggest pain to fab up there there is. Cast is stronger and won't crack, but it'll be easier to have a ramhorn welded up. The easy button would be a TD04 from a volvo and swap in a billet 20T wheel mounted to a T3 flange adapter to an off the shelf 4AGE cast manifold for a T3 setup, this would be very challenge friendly as well. You'd be looking at $150 for the manifold and flange adapter, yards are full of the turbos (grab the intercooler while you're there), $90 for your billet wheel upgrade $60 for the rebuild kit. You have budget left for fueling, EM and plumbing. The turbo will be very happy in the mid-upper 200s, but will start to run out of breathe around 300hp. 

In reply to captdownshift :

How fast would that spool?

In reply to GIRTHQUAKE :

That’s my goal as well short term. May aim for 300 once I go 7a (or 9a if I feel baller)

Fitzauto said:

In reply to captdownshift :

How fast would that spool?

If you want spool, get you some compression. E85 helps too. 

In reply to Fitzauto :

The Volvo TD04 is twinscroll, however the budget manifold options aren't. It's a smaller turbo, stuffing the larger compressor wheel into it will delay response, but going with a billet wheel will get most of it back. If running E85 you should see a responsive setup, it won't be 2.0 Camaro or 2.3 mustang responsive, but it should be subaru EJ series responsive. Chasing spool is more expensive then chasing peak HP, a divided manifold and flange to the twinscroll housing would yield a noticeable improvement in spool, likely at a cost of an additional $8-900 and it'd be far more likely to fail then the cast manifold. 

I'm not *really* looking to make it a challenge-friendly build, I just don't like spending money when there's no purpose in doing so. What I'm REALLY looking for is a good turbo. I've never messed with them, but there's gotta be a golden area of response and power and reliability with an OEM turbo- and Id like to go that way since then id get good gaskets and flanges.

Also, 7AGE parts list.

https://www.facebook.com/notes/aw11-idea-dump/7age-parts-list/1616308338477892/

Why are you going with the 193A versus the 193T? Just curious about the thought process on that decision. 

Any experience with the wrx td04? Getting ready to upgrade my 02 and I’ll just have the turbo sitting around.

It is possible to make near your goal with the SC14, last year I put together an SC12 4AGZE that planted 209whp, 210#/ft, so it could be possible to get what you want... but that engine was not cheap... oversize valves helped considerably.

if the goal is 250whp, on a stock valved 4AGE, it will be less costly, and less mass to run a turbo...  since you are running this in an AE86... mass( or the lack of it) over the front wheels matters.

What are you doing about the rest of the drivetrain?  A T50, and 6.8" Toyota ring and pinion wont last long with the power you are planning, you could go with a Ford 8.8, or possibly a 1st gen Supra rear, or if your pockets are deep, a Weir 28mm axle upgrade with associated differential parts.  The transmission you could use a J160 with a SamQu adapter, or possibly find a W58(or... a 2003+ W55 from the IS300??) 

Where do you typically finish in an autocross??   I have a local friend who has a stock 20V powered AE86 that when he, and his cousin use it to compete in local autocross events, they typically finish in the top 10, and often one of them finishes in the top 5....  

In reply to Fitzauto :

The 4AGE will outfkow an EJ20, so it'll spool quick, but the Volvo twinscroll TD04 will still spool quicker yet. Either option will start to run out of breathe north of 250hp unless swapping in a larger billet compressor wheel .

In reply to oldeskewltoy :

I’m already putting together an 8.8 swap. Blew the stock rear at a road course in October. Trans will be a W-series of some kind.

I typically autocross in Oklahoma City but will be branching out this coming year. I finished top 10 every event with several top 5 finishes but I’m outgunned in power at that point. Hard to compete with a built vette and mustang.

Fitzauto said:

In reply to oldeskewltoy :

Hard to compete with a built vette and mustang.

You do realize this is exactly how you make a small fortune from a big one.... right??     So spending your money.... 

To get, and stay on the podium you will need more then a 4AG...  I'd recommend building a oversize valve 7AG.  Big lift, moderate duration cams with shimless, or shim under...   as too boost... everyone has their choice[s].. as to mine, I'd keep it supercharged, but I'd run a Rotrex,and A2W intercooler to keep installation as compact, and lightweight as possible.  The Rotrex doesn't offer the instant torque of a twinscrew, but does offer a consistent(reliable) powerband.

In reply to oldeskewltoy :

That would be the dream build. As silly as it sounds I’m trying to win on a budget