Jackal's 20g to 18g e85 Soap Opera

[BBPeik]

Well judging from that it looks as if the 18g is the way to go. Nice work

Thanks

[eckseleven]

I think this matches up with what fahr_side has said. Our exhaust cams hinder flow too much for a 20g to be worth it. Something like that.

[GTEASER]

fahr_side has said that our motors don't benefit from the 20g until STI cams are installed. This seems to support that.

[BBPeik]

Of course doesn't it figure. Swannee's motor I am installing has the STI intake but not the exhaust

[GTEASER]

IIRC the STI exhaust cams are the same as ours. Only the intake cams are different.

[BBPeik]

Well I stand corrected then. I guess I am good to go.

Thanks for making my day

[GTEASER]

Verify with Mike Sprank, but I think that's what the discussion was.

[BBPeik]

He did build the motor so I imagine he would have done the exhaust cams if they were needed.

[mcg_]

IIRC the STI exhaust cams are the same as ours. Only the intake cams are different.

 

ahhh, I was pretty sure it was the other way around. See below.

 

The FSM gives the following info on the cams:

 

Intake

46.55 — 46.65 mm lobe height

Exhaust

45.85 — 45.95 mm lobe height

Cam base circle diameter:

37.0 mm (1.457 in)

 

So, lift for intake is 9.55~9.65mm while exhaust is 8.85~8.95mm. Commonly available specs for the EJ257 cams is 9.60mm lift for intake vs. 9.8mm for exhaust. So, it seems the '10 LGT motor lost quite a lot of exhaust lift in exchange for the added AVCS.

 

I wonder if dual AVCS EJ257 exhaust cams would fit the E25 heads...

[mcg_]

And here.

 

You can certainly use AVCS tweaks to improve spool or low rpm torque. The top-end airflow though... you use the same techniques on either turbo it all comes out the same. You can't make up for the loss in duration and 1mm less lift compared to the old single AVCS or STi D-AVCS unit. The only solution I see for this is using the STi exhaust cams or going aftermarket.

 

I've tuned both. The 18G spools a tiny bit faster but flows as much air. This motor is so limited by the exhaust cams that the extra compressor flow is useless.

 

Only the exhaust cam profile is different from other EJ255 / 257 engines. The valve springs are also different from the STi items. '08~ STi cams drop straight in. The drive slot for the oil pump is on the passenger side intake cam only and is also present on later STi cams. We had compared the GRB and BR9 intake cams and they appear identical, and lift is measured as identical.

 

 

Sent from a device using some software.

 

The stock VF-54 exhaust housing is I think more of a restriction than the manifold, so until you move to something bigger, replacing the manifold is something of a band-aid to a boost control problem you may or may not run into.

 

Just FYI, the stumbling blocks to power in this platform are a little different from the 4th gen that preceded it.

 

1. The turbine housing is a P18, about the same as the earlier VF-40 item in having a roughly 7.5cm2 nozzle area. Where on the 4th gen the housing is a universal Subaru fitment, common to the Impreza platform and with OEM and aftermarket housings available up to 10cm2, the VF-54 flanges are unique. Not even the new WRX shares these flanges. The largest turbine that fits 'nicely' into this housing is a TD05H or maybe a 'small' GT30 wheel, AKA the GT29 wheel. Beyond that the geometry is horrible and leads to poor spool and not much better flow.

 

2. The exhaust cams on the 5th gen LGT motor are 1mm shorter on lift than on all other 2.5 liter turbo Subaru motors. They are more like oldskool EJ205 cams in profile. If you've ever read about oldskool 'hybrid' engines, built from EJ255 blocks and EJ205 heads, and how they fall down at high revs, you know what that means.

 

The above two factors mean that fitting larger compressors, that flow more air than the exhaust flow can cope with, only decreases efficiency and increases both EGBP and EGT. Cramming more air into the engine does not help when there is so much restriction to exhaust flow. I have tried both 18G and 20G compressors on the same car, with the same TD05H hotside, and gotten exactly the same airflow, power and 100~200kph times out of both. For this reason I would advise you to stick with an 18G wheel, to enjoy the same power as the 20G with better response. At this sort of power level you will not see much if any improvement from an aftermarket catback, and using the stock catback will pretty much obviate any boost creep problems.

 

If that's not enough power then go to a combination of larger manifold with non-stock flange, larger exhaust housing, larger turbine, and at least the STi exhaust cam. Since you need to pull the motor to swap the cams, this is point you build the shortblock.

[GTEASER]

I knew someone would regurgitate that info. That stuff needs to be saved for the future.

 

mcg_, Do you mind putting all of it in the "Performance Mods" Sticky?

[jojorios]

Just so I'm understanding, putting in 08+ STI exhaust cams, which should drop right in, would be the way to go when going 20g to gain the extra performance from it compared to a 18g? Without the STI exhaust cams, the 20g will not produce as well as an 18g?

[jackal8788]

Just so I'm understanding, putting in 08+ STI exhaust cams, which should drop right in, would be the way to go when going 20g to gain the extra performance from it compared to a 18g? Without the STI exhaust cams, the 20g will not produce as well as an 18g?

 

Yep, that's the gist of it. The 20G may produce equal to the 18G billet but it will be a bit more laggy due to the larger compressor wheel.

[BBPeik]

Well I guess I am back to being equal to an 18g. Still not a bad place to be mind you. That is until I decide to find some sti exhaust cams and install those too.

Damn Enablers:lol:

[BBPeik]

This also does beg the question. If the Sti intake cams are the same then why would M Sprank go to all the trouble of slotting an Sti cam so that it would fit out motors?

[fahr_side]

Note that you still cannot easily run a larger exhaust housing, certainly there is nothing out there fits the stock header. So, while the exhaust cams will certainly give you a bump in output the flow balance between hot and cold side flow is better on the 18G than on the 20G. Ask anyone who's run a TD05-20G on an oldskool 2.5 WRX, EGBP and EGT can really get out of hand. Those guys barely get away with it using 8cm2 housings and unfortunately the housing on the VF-54 is only 7.5cm2. Note the turbine efficiency is also going to be off a little since the housings are custom machined to take the bigger (than stock) TD05H wheel. That's never going to work quite as well as a housing designed specifically for the turbine.

[fahr_side]

This also does beg the question. If the Sti intake cams are the same then why would M Sprank go to all the trouble of slotting an Sti cam so that it would fit out motors?

 

None of the aftermarket STi cams I've seen have those drive slots, since the STi doesn't need them. IIRC S2baru had to slot his Stage 1 passenger side cam as it did not come with a slot. Now, if Mike had slotted a stock STi cam to use in the W25 heads, that was indeed a waste of time. We measured the lift on the BR9 intake cam vs. the GRB item and it came out the same. While we have no equipment to measure duration the cam profiles look identical side by side.

[jojorios]

Looks like my 20g may go up for sale and look for an 18g for the future.

[BBPeik]

Well I just talked with Swannee. He remembers ordering four cams when they did the motor. I am getting a bit of conflicting info between him and M Sprank. We can't find the paperwork. I am sure we will figure it all out. More for my curiosity than anything else.

[jackal8788]

Does anyone know offhand what the thread size and pitch are for our exhaust flange studs? Does M10x1.25 sound correct? I had a small exhaust leak this morning and I found one of the nuts had loosened just a bit. I snugged it up, but I'm thinking I may double up with some copper exhaust nuts beneath just as insurance.

[BBPeik]

I think its m12x1.25

[FLlegacy]

12 x 1.25 is the shift knob, I think the exhaust bolts are m10 you could always take one to the auto parts store and use their thread sizer.

[jackal8788]

12 x 1.25 is the shift knob, I think the exhaust bolts are m10 you could always take one to the auto parts store and use their thread sizer.

 

Thanks. I just wanted to get the nuts on order right away without crawling under the car, dropping the skid plate, and taking a measurement or removing the old nut. Surely not hard, I'm just being lazy

[FLlegacy]

I have a whole bucket of spare bolts and nuts...at home in my shed, lol.

[mcg_]

I really wish we had a sticky thread on fifth gen LGT bolt sizes that somebody actively, thoroughly maintains. NOT IT. Seems like these questions get asked a lot on here.