New Autocross Turbo: VF39, VF43, 20g???
 

OK, my stock turbo is cracked in 3 places...

Need to make a quick decision: Input, other options and comments welcome) I will be researching for the next couple hours....


VF-39 (Same as stock, spools quick, prone to cracking apparently, drops off at 55000, SP legal, $950)
VF-43 (Same as '07 stock, spools quick, cracking probably the same, less prone to boost creep due to new wastegate, SP legal, $???)
18G ( Spools as fast if not faster, Solid design, flow???, Welcome to SM, need injectors???, $???)
20G ( Spools slightly later, Solid design, flows longer, Welcome to SM, need injectors, $1800 or so)

I am thinking the VF39 is out since I can use a VF43 due to update / backdate. And yes, since the long block has the same PN, I don't believe I have to swap the engine.

20G is interesting but puts me in SM where I still believe the STI is not truly competitive vs. say a 500+ HP 2500 lb. car.

For an autocross car, I think the most important thing is space under the HP curve. Or how early does the power come on, and how late does it stay.

The longer you can stay in 1 gear and be efficient saves seconds vs. shifting.

Anybody following any other forum discussions on the options?

Reading this right now.: http://forums.nasioc.com/forums/show....php?t=1141476

Dean, the additional power of those bigger turbos is pretty useless for autocross IMO. For example, I'm probably 30hp at the wheels more than Matt, Mike and Eric, and they've still got the power advantage over me because they have earlier and bigger torque w/ their stock turbos vs. my 20G.

I'd go with something smaller if autocross is your goal. Staying in BS might be a good idea, but PAX between BS and SM really isn't all that different.

If you're thinking of SM, I still have that SBR GT30-10 I'll sell you for dirt cheap... it'll spool faster than stock and make similar power. But GST Mike will hate you for having to tune a 2.5L with that undersized turbo again... :lol:

Dean, try the 43!!! I think it will be ruled BSP legal from what I've been reading, and I think it is going to be the hot ticket in SP if it is indeed okay to run.

Scott, I think you meant to say BSP, not BS, but just making sure.

43 43 43 43 43 43 43

I think the choice depends on the answer to 2 questions:

1) how much do you care about autocross?
2) are you prepared to run 100 octane at autocross events?

If the answers are "a lot" and "no", then you really have no choice, get a VF39/43 (whatever you can find cheap) and stay in street prepared.

If the answer to number 1 is no, just get a 20G or green sized turbo and have a great track car. If you are prepared to run 100 octane I think either a 20G or green will actually be competitive in SM, especially at a local level. nasioc link with charts. For either sized turbo you will probably need injectors/intercooler. If you add 100 octane you will probably need a bigger maf housing as well.

Don't waste your time with an 18G. It is way too small for the 2.5L engine. It will be in the same ballpark as the stock turbo but in a different class.

Or you could just do the sensible thing and ask Mike W for his opinion :)

That may likely result in something with 6 cylinders. :lol:

I am talking to GST & Mike, that is where the car is right now. That's how I know it is cracked, they were in the process of doing the headers and turbo back.

They are working on prices for the options and will have something for me in the AM, but thought I'd toss it out for discussion.

Not sure why you would need a rulling on the VF43. From what I can tell it is clearly within the update backdate rules. According to GST, the long block part number from Subaru is identical from 2004-2007. The rules only permit the change in turbos in conjunction with the engine from the same year. Since the engines are the same, the turbo change would be permitted accross the year range.

The blocks may have the same part number, but are the heads identical? Cams? Valves? Timing gear? ...you see where I'm going. In update/backdate rules, you have to swap the *whole* engine along with the turbo... so if there are *any* differences between the '04 and '07 motors you're in trouble (or SM as the case may be).

Long Block = whole engine including heads last I knew. Does long block man something else in the world of boxter engines? If the long block part number is the same, then that would stand to reason they are the same engine at least from a rules perspective.

I'm hoping to get a printout of both parts "pages" out of the parts list with the long block part numbers.

has anybody seen any discussion on this on Nasioc, or SCCA Forums?

Try ordering a new plastic coolant reserve tank with it's specific part number from Subaru... you'll probably get one of the older/larger metal tanks because they linked the p/ns. My point is, part numbers aren't the end-all method to verify anything.

Hell, I'm running into the same issue w/ the legacy tranny I put into the SVX... everything part number related tells me the tranny is a 4.11:1 gear ratio, but when it's attached to a 4.11 rear-end, the center diff binds, indicating it may actually be a 4.44. If the same tranny with the same part number came as both a 4.44 and a 4.11, who's to say the '07 long-block assembly won't carry the same p/n as the '06, yet have different parts inside?

I'm not saying it's illegal, I'm just saying you're probably better off waiting for things to be sorted (the '07s aren't even out yet!) before making a decision about the update/backdate of the turbo... or since waiting isn't an option, at least realizing that there's a chance you'll end up in SM, or selling that VF-43.

From what I have read, the differences in 07 are the turbo wastegate, the ECU, and the gear ratios (2-3-4 are taller, so there is no longer a huge gap between 4th and 5th, 4th now tops out at 117 mph instead of 99). The rest of the drivetrain is identical. I know it's true because I read it on a forum on the intarweb.

The 20g is to big for auto cross..friend has one on his car pulls hard but not fast enough for auto..
The 18g is a good turbo. you will be able to run up to 27psi on it(more than you will need for a wrx). The spool is close to stock (for an evo) the WG is at least 10.5 so it will be a steady boost curve.

Just trade me entire engines Dean... Then you'll have NO TURBO LAG AT ALL!! :lol:




Honestly tho, it even makes sense to me that some HUGE turbo that takes any more time than stock to spool is un-sensible for auto-x. I've heard WAY too many people complaining about stock WRX spool rate at auto-x, and I wouldn't think you'd wanna do that same thing to the STI...

I'm proof. My 20G is a bit large for autocross, and I went with the quicker spooling TD05-20G instead of the more popular TD06-20G just so I wouldn't have a totally useless autocross car. Lag is just a little better than the stock 2.0L WRX was... but at least when the boost comes on, it really comes on.

No $H!T ! :eek:

I keep thinking maybe it is time to strip this sucker, put in a cage and run FP...

Funny... I keep having that thought too... except, I'm not sure if I can run a WRX with an STi motor, as I think I violate the maximum overbore rules in 17.J, and it seems porting/polishing of the heads is illegal as it's not mentioned in 17.H... so it looks like it's SM for me! :lol:

Scott's right about the engine. I would expect that somewhere in the motor some component is slightly different in some small way, and the VF43 won't be legal without an '07 block. Besides, now that everyone thinks the 43 is a better turbo, they will probably go for twice as much as a 39 at this point. Also, remember that there are two versions of the VF39- decide which exhaust housing you want before you buy one, and verify it before you pick it up. Either should be okay for BSP because it was a midyear switch, so there probably werent any changes to the longblock mid-'04... but you never know.

Technically, it is about documentation, not actual parts. If from a manufacturer part perspective, the part is the same, it is the same, no matter how many components or even the single part is different. Even if there is a part number change, but you can provide documentation of that change and that the replacement part number is an the official replacement part for the original part, it is OK.

Many long or short blocks from manufacturers provided for warranty or non-warranty are "rebuilds" anyway and may or may not contain all new internals. So if I order an '07 long block, it is entirely possible that the serial number on the block may be an 04 serial number with '05 parts that they rebuilt it with.

None of that changes the fact that the part number for the replacement long block for an '07 theoretically is the same as that for an '04.

My guess is that the VF43 will become either "an" official replacement part, or "the" official replacement part for the VF39 for all years at which it really becomes a moot point.

If SCCA only cares about the part numbers, you should be able to run the 43 with no problem.

Ok, ok does this mean I can increase my turbo size? O, please say yes!.. :huh:

Sorry, the WRX only ever came with a TD04-13g. But I think you can update/backdate to the 2.5L motor if you want.

Yep, you could drop in the 2.5l engine in SP unless they split the years in the 07 rule book which still aren't posted on the SCCA web site.

So if they put the 06 WRX on a different line I'm out of luck?

Yes.

Trading your car for a used STi would be 18! times better value than a motor swap but cost around the same amount.