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Old 09-07-2010, 04:32 PM   #1
Motion Lab Tuning
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Default Motion Lab Tuned: HTA68 2.5L vs 2.1L (Stroked), same day results, same dyno

HTA68 Turbo on a 2.5L vs 2.1L

We tuned both of these cars on the same day, within an hour of each other. We thought you guys might like to see a fair comparison of how the HTA68 performs on the two different motors. These cars have similar mods including the turbo, just the difference in displacement. Below you will see the dyno charts and a comparison of the boost levels between the two. First off for a full mod list of both cars.

2004 WRX with a 2.1L stroker (79mm crank):
Short Ram, TBE, HTA68, MLT 750cc Injectors, STI cams, MLT 3-Port EBCS, Stock WRX TMIC

2004 STI with 2.5L: HKS intake, BC 280 cams, MLT 820cc injectors, MLT 3-Port EBCS, Stock STI TMIC


Ok now for the graphs:

Here is the 2.1L Final Pull:



And Here is the Sti final Pull:




And here is the comparison between the two:




As you can see the 2.5L made much more torque while the 2.1L made pretty much the same peak HP. The boost just drops off on the 2.5L while the 2.1L held boost much better. To see this even better here is the Boost Graph comparing the two!

Boost Graph Comparison:


You can see the 2.5L spools about 500 RPMs quicker than the 2.1L and if you refer to the power comparison you can also see the peak HP on the 2.5L comes about 500 RPMs sooner than the 2.1L as well. Although we think that the HTA68 is a nice daily driver turbo on the 2.1 or even a 2.0L, it really dies off too hard up top on the 2.5L

Jordon @ Motion Lab







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Old 09-07-2010, 04:35 PM   #2
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interesting. why do you think the turbo on the 2.5 falls off so much quicker? is it the bigger cams out working the turbo?? more restrictive tmic? just asking, idk
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Old 09-07-2010, 04:45 PM   #3
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There should be some significance between stock sti cams and 280 cams (on the 2.5). Interestingly the only real difference being down low. Did the revability of the more square (bore/stroke ratio) 2.1 cancel out the extra duration of the 280 cammed 2.5? I would be interested to see if there would be a more pronounced difference if the cams were switched the other way around.
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Old 09-07-2010, 05:16 PM   #4
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Quote:
Originally Posted by RLR257 View Post
interesting. why do you think the turbo on the 2.5 falls off so much quicker? is it the bigger cams out working the turbo?? more restrictive tmic? just asking, idk
Uhh... larger engine = more airflow = hits the flow limit of the turbo sooner. Any other major restriction would have shown itself in peak HP.
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Old 09-07-2010, 05:26 PM   #5
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Originally Posted by autowagon View Post
There should be some significance between stock sti cams and 280 cams (on the 2.5). Interestingly the only real difference being down low. Did the revability of the more square (bore/stroke ratio) 2.1 cancel out the extra duration of the 280 cammed 2.5? I would be interested to see if there would be a more pronounced difference if the cams were switched the other way around.
You can see the difference in the cams at 6500 on the last chart. on the 2.1L 6000-6500 RPM, drops ~1psi, 6500-7000 RPM the boost is flat, this is an indication of restriction somewhere. The RPM dependence suggests the heads. In this case, higher boost is the result of the restriciton. Higher boost pressure isn't always good.

On the car with cams, the boost continues it's falloff at the same rate, indicating no major restriction. This is where the cams are helping. Since there's no major restriction from the heads where the peak HP happens, the cams didn't buy anything there... the heads flow well enough there, so you are seeing the turbo restriction.

STi cams are good for a VF39-ish / 16GEvo3-ish sized turbo. It takes something larger to push the head restriction significantly. Juan showed this pretty convincingly when his heads were built and he picked up little to nothing on his vf39. You need a bigger turbo to see major cam improvements. Ports are on the small side on the USDM heads, I think this is just as much a restriction as cams are.

I'm no expert, but I think if you switched the cams around you still wouldn't see a significant difference. The 2.1L would probably have slightly more HP at 6500+ and the 2.5L will taper more at 6500+, but neither engine matters a whole lot that high with an HTA68. The smaller bore for the 2.1L is already showing it's advantage in the upper RPMs.

Personally I'm surprised to see even 500RPM difference in spool. I assume the 2.1L was without AVCS? How much difference do you think AVCS tuning plays in the role of the spool? I wouldn't expect much, but I haven't had any experience with AVCS tuning.

Last edited by Concillian; 09-07-2010 at 05:36 PM.
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Old 09-07-2010, 06:07 PM   #6
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based on what i have driven avcs plays a huge role on spool. my friends sti with same turbo as me feels like a completly different car down low. should have done full conversion instead of hybrid
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Old 09-07-2010, 06:16 PM   #7
Dave D.
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The 2.5 really benefits from a 10cm^2 hotside; this is more proof IMO. Or, I'll bet if you run E85 you'll see dramatically different results.

10cm^2 hotside > cams.
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Old 09-07-2010, 06:18 PM   #8
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Quote:
Originally Posted by Concillian View Post
You can see the difference in the cams at 6500 on the last chart. on the 2.1L 6000-6500 RPM, drops ~1psi, 6500-7000 RPM the boost is flat, this is an indication of restriction somewhere. The RPM dependence suggests the heads. In this case, higher boost is the result of the restriciton. Higher boost pressure isn't always good.

On the car with cams, the boost continues it's falloff at the same rate, indicating no major restriction. This is where the cams are helping. Since there's no major restriction from the heads where the peak HP happens, the cams didn't buy anything there... the heads flow well enough there, so you are seeing the turbo restriction.

STi cams are good for a VF39-ish / 16GEvo3-ish sized turbo. It takes something larger to push the head restriction significantly. Juan showed this pretty convincingly when his heads were built and he picked up little to nothing on his vf39. You need a bigger turbo to see major cam improvements. Ports are on the small side on the USDM heads, I think this is just as much a restriction as cams are.

I'm no expert, but I think if you switched the cams around you still wouldn't see a significant difference. The 2.1L would probably have slightly more HP at 6500+ and the 2.5L will taper more at 6500+, but neither engine matters a whole lot that high with an HTA68. The smaller bore for the 2.1L is already showing it's advantage in the upper RPMs.

Personally I'm surprised to see even 500RPM difference in spool. I assume the 2.1L was without AVCS? How much difference do you think AVCS tuning plays in the role of the spool? I wouldn't expect much, but I haven't had any experience with AVCS tuning.
very informative, thanks for clarifying this for me.
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Old 09-07-2010, 08:56 PM   #9
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Quote:
Originally Posted by AWDWRXLOVER View Post
based on what i have driven avcs plays a huge role on spool. my friends sti with same turbo as me feels like a completly different car down low. should have done full conversion instead of hybrid
Is this torque or spool RPM though? I know AVCS has a large affect on off-boost and low-boost torque, the advance really helps quite a bit down there...but I don't know how much affect it has on actual spool RPM.

You feel torque as much as you feel spool RPM. You need a reasonably controlled test to separate the two.
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Old 09-07-2010, 10:47 PM   #10
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Quote:
Originally Posted by Concillian View Post
Uhh... larger engine = more airflow = hits the flow limit of the turbo sooner. Any other major restriction would have shown itself in peak HP.
thats what i was leaning toward, i.e. more air flow. i was asking because i wasnt sure. so i was just looking for confirmation. thanks.
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Old 09-08-2010, 01:13 AM   #11
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too bad the 2.1l stroker still had the stock tmic, i think even a sti tmic would have helped a bit overall.
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Old 09-08-2010, 12:47 PM   #12
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Nice comparison. I wish it was a better turbo, and the 2.1 revved out a bit more.
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Old 09-08-2010, 01:07 PM   #13
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I'd love to see both of these cars retuned for E85. Same circumstances.

Same day, small time gap.

Thank you very much for the information. Awesome post.
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Old 09-08-2010, 06:35 PM   #14
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Hey everyone! I'm the guy with the 2.1L stroker. If enough of you say you want to see the 2.1L on e85, I'll gladly switch maps. The only reason why I'm so hesitant about running the e85 is because I'm originally from NW Indiana, and there are far to few gas stations along the way that offer the e85. I would basically have to plan my route around gas stations that provide the e85.

If you all really wanna see it run on e85 lemme know, or PM Motion Lab. I'd also like to find a bigger TMIC, so if you have one laying around or know someone that is selling theirs definitely let me know.

Alex @ Motion Lab
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Old 09-08-2010, 07:39 PM   #15
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Letting you know that I would Alex !
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Old 09-08-2010, 09:35 PM   #16
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Thanks for doing the comparison guys. I'm kinda thinking, though, that both cars should be spooling quicker- at least on the street. And if so, that could potentially change the difference in spool, no? Alex, at what rpm does your car hit full boost in 3rd gear on the street?
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Old 09-08-2010, 11:40 PM   #17
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I think between 3500 and 4000 rpm on the street. I'll have to take a look at it tomorrow to give you a good answer.

Jason - I'm originally from the Valpo area. Nice to see some Indiana Impreza people taking interest
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Old 09-08-2010, 11:44 PM   #18
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wish there were more 2.0's on the hta68. which hotsides are you both running on the 68's?
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Old 09-09-2010, 12:10 AM   #19
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Quote:
Originally Posted by Phoenix Rising View Post
Hey everyone! I'm the guy with the 2.1L stroker. If enough of you say you want to see the 2.1L on e85, I'll gladly switch maps. The only reason why I'm so hesitant about running the e85 is because I'm originally from NW Indiana, and there are far to few gas stations along the way that offer the e85. I would basically have to plan my route around gas stations that provide the e85.

If you all really wanna see it run on e85 lemme know, or PM Motion Lab. I'd also like to find a bigger TMIC, so if you have one laying around or know someone that is selling theirs definitely let me know.

Alex @ Motion Lab
If you decide to do E85, you could get 2 5 gallon gas tanks and fill 'em up. You shouldn't need a full tank to change the tune.

I wish I had my Process West intercooler already, I'd sell you my STi TMIC for ultra cheap just to see the new tune.

PLEASE DO an E85 tune!!!!!!!!!
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Old 09-09-2010, 12:13 AM   #20
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Inthenameofweez - When are you getting the Process West intercooler?
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Old 09-09-2010, 01:07 AM   #21
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Quote:
Originally Posted by jason miller View Post
Thanks for doing the comparison guys. I'm kinda thinking, though, that both cars should be spooling quicker- at least on the street. And if so, that could potentially change the difference in spool, no? Alex, at what rpm does your car hit full boost in 3rd gear on the street?
Ditto,...
I know it depends on dyno and loading blah blah blah
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Old 09-09-2010, 09:30 AM   #22
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concillian is primarily correct, as a cam would only change so much when that turbo just doesn't have the size/flow up top
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Old 09-09-2010, 09:48 AM   #23
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Quote:
Originally Posted by karlknaupp View Post
wish there were more 2.0's on the hta68. which hotsides are you both running on the 68's?
We're running a 7cm standard hotside Subaru fitment.
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Old 09-09-2010, 09:49 AM   #24
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Quote:
Originally Posted by jason miller View Post
Thanks for doing the comparison guys. I'm kinda thinking, though, that both cars should be spooling quicker- at least on the street. And if so, that could potentially change the difference in spool, no? Alex, at what rpm does your car hit full boost in 3rd gear on the street?
Just did a quick pull taking a friend home, and I'm in full boost right around 3800 rpm.
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Old 09-09-2010, 07:28 PM   #25
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That's kinda strange. I would expect a stock ej205 to spool that turbo around 3700-3900 rpm. I was thinking your stroker motor would spool it up a bit quicker. Is your exhaust tapered and/or catted? I wonder what the spool is like for that sti on the street...
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