Todd said that the extrude helps above 5k. He also once said that the bigger plenum and throttle body help above 5k but other times he doesn't give them any endorsement so I guess it depends on what day you ask him, lol.

 

Well, it actually makes sense. Most of the conversation here about performance parts focuses on how much power a part "adds" or "makes". Generally the label "every car is different" gets tossed around as well. There is very little discussion as to what is actually going on. Part of that is the high end automotive market tends to favor professional tuners, and part of it is those professional tuner's don't like to share much data. Todd is one of those guys that shares information, and that is one of the reasons I like dealing with him the best.

The turbos compressor sides are (mostly) separate from the engine volumetric efficiency. Replacing the plenum, throttle body, and y-pipe for example will make the engine flow better. $3,000 better? Not really in my opinion, but that's a separate conversation. So let's say that we've done the three above mods and then re-run my log. What you would see actually is boost going lower - the engine is flowing more air, and the turbos are still at max flow.

Ultimately there is a pressure differential between back-pressure in the turbines/exhaust, and pressure going into the intake manifold. That's why you replace the exhaust in the first place, to relieve back-pressure and help that ratio. For example, you could shrink the turbine side by closing the variable vanes in the turbo. This would lower overall flow, and raise boost. You wouldn't make any additional power in that scenario, and it would be harder on the equipment all things being equal.

The basic idea is to maximize the flow rate of the engine from the air filters to the exhaust tips, and then throw as big of a compressor at it as you can.

If you were to extrude hone the turbines on the turbo without upgrading the compressors you would see boost lower much further - probably a much larger amount than the y-pipe, plenum, and TB. To say it a slightly different way than above, we've now raised the flow capacity without changing the turbo's supplied mass flow rate appreciably. As a result it will now be more difficult to keep positive pressure in the intake manifold, as the engine as a system is now flowing more air per revolution.

The upgrade to the 67mm compressors will allow it to hold more boost, but the amount of boost is arbitrary compared to flow rate. What can you do to raise the overall flow rate (volumetric efficiency) of the engine? You can upgrade the exhaust, intercoolers, inlet pipes, throttle body, y-pipe, larger turbine wheels/housings, high flow cats, exhaust, etc. Getting more intrusive you can also replace the cams, port the heads, run oversize valves, stroke the engine (3.8L, 4.0L) etc. Those more intrusive modifications wouldn't do as much for you as they could (or anything), if for example you were still running stock catalytic converters. The least flowing item in any system is going to dictate maximum flow.

What may appear at the surface of Todd recommending parts in one case and not another is where the customer is in this careful balancing act. If I put a plenum, throttle body, and y-pipe on my car it wouldn't make an appreciable difference in peak horsepower numbers. It might do a little better down low torque wise. If I were to upgrade to the 67mm compressors though - they might be worth an extra 20-30whp in aggregate as the 67mm compressors would be able to support the extra flow capacity.

Hope this makes sense,
Dan

 

Yeah i have the TB and plenum on my car. It did, on the dyno, add 10whp or so. But $/hp its NOT worth it. I did it b/c what the hell.
I asked him about the extrude and he said it would help, but not enough to be really worth the time, at least for me as I'd have to pay labor and we'd need to retune. He said if I'm going to spend any more $$, to just buy the alphas.

And I agree mostly w/ Rix's assessment, but PSI is not the only judge of power. 67mm turbos at 22psi and stock 62mm turbos at 22psi are making vastly different power levels. Boost is just the pressure, not the actual volume of airflow. Volume = pressure over surface area. 67mm is much larger than 62mm, so same pressure from those turbos, the 67mm is flowing much much more air which = more power.

 

Correct, I was trying to simplify greatly as well. Sometimes I get carried away and write a wall of text. Temperature matters quite a bit too, I'm sure your 67mm turbos don't heat up the intake charge nearly as much as the stockers do.

I still want a plenum, y-pipe, and throttle body though.

 

Hah. The y-pipe, because its such a simple install you can do yourself in 30 mins, I would do anyway. $950 or whatever from IPD and you're set. TB/plenum is a pain to install, so probably not once you factor in retune and the minimal gains.
You're maxing the stock turbos anyway, not going to free up too much more power.

 

The plenum and throttle body aren't always a bottleneck...I believe Dave (ttdude) has stock plenum and throttle body with his a3076 turbos on e85. So it does depend which turbos are being talked about when Todd makes a recommendation.

 

Yeah my car made 983 whp on Todd's dyno with stock plenum and TB. It would probably benefit with a larger TB and IPD plenum but for an extra $2K, I'd rather put that toward a set of new lightweight wheels.

 

Agreed. The parts are simply overpriced. You'd make a little more power, but the $/hp ratio is not very good. Now that the 997 is the new 996, I am looking forward to some new parts and more competition bringing the prices to a more reasonable level.

 

Well. Apparently I was just being silly testing the car in the 90*+ weather.
Borrowed the vbox, found a road with a .5% uphill grade, and clicked off one run. Didn't even bother doing any more and risking getting unwanted attention.



Log has been sent to mike for verification and will soon be on the official board. 6.02 60-130, 5.1 100-200. I'm sure had I done a few more runs that there was a 5.9X 60-130 in her. Maybe another day.

Also did this 4th gear only, so at 60 its not at full boost yet. I'll go try a 3-4 another day in an effort to get into the 5 seconds.

Still stock wheels so there's another bump in time if I ever buy lightweight ones (I wont lol)

 

Great time! That's almost a full second from what I could do with 63.5's/MS109/4th gear pull.

PS Just noticed but your peakG's and velocity seem odd?

 

Here's the charts for 60-130 and 100-200.
It was a long logging session - drive to the road, ensure no traffic, do a run. I aborted the first run, so drive around and go back to the spot and go again. Didn't stop and have it reset during that time, hence the low avg.
Peak G i'm not sure why its showing .4. In the data, during the run its got .819.

 

Any update? I'm doing an even lower budget E85 setup.

 

Woops wrong thread.

 

No real update, I'm just driving the car at this point. It's still running perfectly, still faster then anything else I've met in Mexico.