hokiruu

iTrader: (19)

I am interested to see what people's opinions are on AutoX purpose- built engines in terms of strokers/displacement and lower end torque vs. built 2.0 for a higher rev range. While the tons of low end tq. and fast spool of a stroker sound like they could be beneficial, only if it is usable and there are occasions when it definitely is not, and topping out the RPMs on a stroker could become a concern.
On the other hand a built 2.0 can rev to the sky, but how would you set one up for autoX in terms of turbo selection? Probably some courses would favor one over the other, but to build one to take whatever autox course you throw at it, with what is proven to be fast approach to driving them, how would these engines compare and how would you set them up?
I am NOT in the market to do so myself, this is strictly for the sake of discussion, primarily with Street Mod in mind.

evobeatsti

iTrader: (7)

if your building a serious autox car, also remember that if you go up in displacement, your min weight requirement also increases, just a thought

hokiruu

iTrader: (19)

oh yeah. good point. thanks for mentioning that. any comments about the engines?

Ludikraut

iTrader: (17)

I think the answer really depends on if you're going to leave the stock gearing alone, or if you're also going to change the final drive ratio. IMO, if the rev-limit is a potential issue (i.e. necessitating a shift into 4th, for example), then the built 2.0 is the better option, given the stock gearing. Although a stroker mated up to something like a 4.11 FD would probably negate the RPM concern for Auto-X.

In either case, it really comes down to a balancing act between rev range and usable power. Something like a GT30R turbo could give you a usable powerband from about 4000 RPM all the way out to between 8500-9000 RPM on a 2.0. That same turbo will spool up maybe another 300-500 RPM earlier on a 2.3L, but fall off earlier as well, giving you maybe something like a usable powerband of 3500 RPM to 8000-8500 RPM. Of course, if your 2.3 is limited to a 7500 RPM redline, then you only have a usable powerband of 4000 RPM versus 4500-5000 RPM on the 2.0. This discreptancy only gets worse with bigger turbos.

l8r)

Matt2.8NJ

iTrader: (7)

I'd start by thinking about where you end up in terms of max speed on course, and not just RPM in gear... making power all the way to 72mph or so would be great for national size courses... but hopefully not at the expense of midrange "oomph".

hokiruu

iTrader: (19)

Good posts. Ludikraut thanks for mentioning gearing, especially in specific detail. I intended to ask about that as well, but got rushed at the end of the post and forgot.
It seems that the target hp range for a nationally competitive SM car is between 400-450whp, and of course a smooth and broad powerband with a pretty flat torque curve. Seems like 50 trim, maybe the upper limits of a maxed out green turbo territory. What about twin scroll setups (desides the obvious stock-based turbos, I'm talking external wastegate)? While TS seems to fall off in the upper range a bit its faster spool relative to turbo size makes it seem like it could be good AutoX candidate technology. Would you agree?

Ludikraut

iTrader: (17)

A TS 3076 on a 2.0 liter won't fall off noticeably, if at all, versus an open scroll variant.

I'm very happy with my 50 trim, but I'm not sure if it has fast enough spool up for auto-x. I'm guessing that something like the Full Race TS 3076 would work slightly better (faster spoolup, better transient response), with the same, if not slightly better powerband. And to clarify, by faster spoolup, I don't mean earlier spoolup, instead I mean that once it starts to spool, a 3076, especially a TS 3076, should hit full boost faster than a 50 trim. For my purposes I prefer the more gradual spoolup characteristic of my 50 trim, but for auto-x, I could see wanting the faster response.

A maxed out FPGreen should be pretty good too, but it will need racegas to make that kind of power (400-450) range.

l8r)

DaWorstPlaya

iTrader: (31)

I'm going to answer this question with the condition that everything else in the car remains unchanged (gear ratios, etc). I would rather invest in the 2.3L stroker and either mate it up with a EVO9 turbo or FP Green turbo. IMHO, a quicker spool and more low end torque would be slightly more beneficial (depending on the course).

With the built 2L you could rev higher and thus gain a higher top speed using the same gear ratios but low end torque might not improve (depending on compression ratios). What was that saying, there is no replacement for displacement ...

hokiruu

iTrader: (19)

After reading a bit more, perhaps 400-450 is a bit high. High 300's to low 400's whp seems more than sufficient. shame everyone tends to think and speak in terms of HP first, when it's torque that really determines how the car will behave.

Ludikraut

iTrader: (17)

Yes, but it's torque at the wheels that really determines how the car will behave ... i.e. engine tq + all gearing + tire size.

l8r)

griceiv

iTrader: (2)

I'd be looking for the highest redline possible with a turbo sized to provide the maximum torque in the speed range you spend the most time in. keeping in mind that as you add more low end the time you spend in the slower speed ranges decreases and the time spent in the upper speed ranges increases.

My best guess would be something along the lines of a built 2.0 that could rev to 9k or so and keep the stock gearing. I'd be hard pressed to do anything other then a stock 9 turbo (maybe a hta green) until nationals goes someplace with more space.

a stroker would be a major shoot in the foot move. it would be on the limiter continuously or needing to shift. In addition Hoops and Daddio say that the midrange torque of a 2.0 and a full blast green is already borderline undriveable, i can't imagine what a stroker would be like.

hokiruu

iTrader: (19)

thanks griceiv. yeah, that is one side of the argument i have been hearing more from autocrossers themslves. while a 2.3 seems appealing in theory, it sounds like it would be a pretty narrow margin of what is "right" and usable for autocross with it. seems like a 2.3 with a properly sized (bigger than for autoX) turbo would be better suited for road courses that aren't particularly long, than autoX compared to a built 2.0?

griceiv

iTrader: (2)

i think a stroker would make a great DD motor. for any sort of racing RPM is king IMO. The faster you go, the smaller your power band requirements are thus making bigger turbos more appealing. but you just can't sacrifice max revs for displacement.

shoot, i'd even consider a 1.8 if it meant I could rev to 10k and run a shorter final drive with out having to shift.

Evo_Someday

Maybe I'm mistaken but if you start doing things like stroker and bigger turbo.. won't that move you into a modified class in autocross where you'll get spanked by purpose built racers?

What class did you want to run in autocross?

I've only done 3 autocross events in my Evo so far but I have quickly figured out that engine power is NOT the problem. I'm already having to "baby" the throttle and brake early on my street tires and stock suspension just to keep from getting it sideways or pushing right out through every turn.

I would put all my concentration in handeling first. Just my opinion based on my experiences.

hokiruu

iTrader: (19)

Like I said in my first post, this is NOT for my own current AutoX purposes, and with SM in mind. I just wanted to open the issue for discussion because I'm interested in it. I think that these engine builds are legal for SM.
As for myself, I am right where you are describing yourself regarding power, it's the last thing I need at this point in STU.