now that ive got my setup running great i was wondering about a few things.

would switching the pipes from the turbo to ic to the tb from 2.5 inch to 3 inch make any bit of difference?

do high numerical gear ratios actually hurt a turbo engines power? ive been running 4:10's in the car and have been told the car will make more power with a lower gear like 3:42's

auto vs manual? this one seems 2 sided to me.half the ppl say auto is better with a turbo,others say a manual trans is better.anyone with a turbo setup ever swap from one to the other and see any differnce?

and the last thing i was wondering about was when my motor is makeing full boost 14psi my boost gauge bounces around 13-16 psi really fast. was told this could be a boost leak at one fo the couplers or to small of a wastegate any ideas? i couldnt find any boost leaks and the wastegate is a 38mm

thnx in advance guys

 

Going from 2.5 to 3 may make a difference, but at that power level I think it would be negligible, though I have no solid proof. It would make your boost take longer to reach the manifold, though (seeming like it spooled slower, when in reality that's a false account), as the pressure would simply have more space to fill.

The only time gear ratios hurt power in a turbo car is when they don't create enough of a load on the engine, increasing spool time and possibly limiting full boost. This is usually only a problem in first gear, sometimes second from what I've seen. It's the same reason the turbo usually can't make boost while free-revving the engine (unless it's way too small, my Talon's stock T25 would make 11 psi in neutral with the other mods, lol). If your car doesn't have a problem with this, higher gears won't change the power level at all compared to changing the same gears N/A. If you aren't hitting full boost or it's spooling a bit slow in first or so, it may give you a bit more power there (that you may not want, depending on traction).
This is only relating to power level, not whether or not your car is faster. It may be faster with the lower gears depending (once again) on traction, and where your powerband lies. Turbo cars often like lower gears because they usually have a peaky torque curve, and the longer gears keep the engine in it longer, and turbo cars make lots of torque.

The reason people say auto's are better is that they keep the turbo spooled and making boost between shifts, unlike a manual, and it's also easier to launch with a partially spooled turbo this way. These reasons can lend to a disproportionally faster 1/4 mile time than a manual vs. a N/A setup.
Personally, I say it's all what you want out of your car, which is completely up to you. I like shifting completely on my own and will sacrifice some 1/4 mile time for it. I've never swapped between the two in a turbo car, but I've driven both.

Your boost gauge flickering is probably caused by wastegate flutter. My Talon used to have that problem on the Tial 38mm at 20psi and up with the manual boost controller, but since I got the Profec-B EBC that problem has gone away for some reason. I guess it's one more reason an EBC is better, heh. Your problem may be the same. On my car I could (barely) hear the slight fluctuation, too. What kind of boost control do you have, out of curiousity?

 

its just a ebay 38mm wastegate with an ebay manual boost controller.right now the wastegate has an 8 psi spring.

 

It's probably the same problem I had. While not ideal, I don't think it will hurt anything. I don't know for sure if a bigger wastegate will fix it, but possibly. In my experience, a simple (2-way adjustable) solenoid-operated closed loop EBC did, though.

 

Some things to ask here
A)what's your turbo?
B)what are your engine mods?
C)what mods have been done to your trans?
D)what kind of tune/management are you running?
E)if you're into track racing it what's your mph?
F)what kind of driving do you normally see? (drag, autoX, daily commute etc.)
G)what RPM are you seeing boost at.

With 2.5 inch cold side pipes I doubt you're missing much in regards to boost pressure.

Personally, if it were me I would be looking at a converter if you're running the OEM one. I would be willing to bet that you'll get some decent time out of one, provided you've got a properly sized turbo. I'd put money here first.
I doubt I'd do a manual tranny for a drag type setup, from my understanding the Turbo T/A lost about .5 second when they tried a manual in a prototype. The skill curve for launching one tends to be a lot higher then with an auto.


Gearing is largely dependent on the trap speed of the vehicle, driving sitiuations etc. etc. Yes a larger load on the engine will decrease your spooling time. most GNs I've heard of run 3.42s, and stayed about the same or a bit better ET but lose mph in the 1/4.

 

t04e stage 3 57 trim ar .63/.50
fully ported heads/intake, custom j.e forged pistions - 8.9-1 cr.new springs locks retainers
tci kit/w manual valve body/restalled stock convereter
stock ecm larger injectors/fmu
my mph has been all over the place from 100-112 all in the mid 12 to low 13 sec range
daily driver/weekend warrior
in first gear with the 4:10s ill be at 5-6 psi @ 2,500 and 14 psi by just a tad over 3,100-3200 though im almost my tach is off. just dont know if it reads high or low

 

If your tach is off, it most likely reads high, they usually do that in these cars.

What RPM (indicated, anyway, for comparison) does it reach those boost levels in second and third? Either way taller gears won't give you a power gain, that spools pretty quick anyway and reaches full boost.

 

I noticed your car has a shift kit in it. Does it hold second gear if you put it into second manually? A 700R4 has a very first steep gear, so if it hold second drop it in and see if it makes any difference. Have you got any ideas on why the MPH is erratic? (fueling, boost/exh. leaks, etc.) I'd definitely try to get that locked down before I did anything else. you should be fairly consistent MPH wise, that means somethings up you need to fix.

 

I think he meant that was while he was trying to dial it in. But I'll let him answer.

 

no i cant take off in second gear.if im on the throttle more then 1/2 it has boost soon as it changes gears ill have full boost.though it seems like its being held back on gear changes.i found ou tthough after adjusting my bov if i slightly get off the throttle right as i shift so the bov opens and then closes for a split second during the gear change it goes away .yeah the mph was all over the place well i was getting it to run right.now its avg mid 12's @ 112

 

My experiences with turbos, gears, and transmissions:

with twin chrysler t3's (powerband: 2600-4800rpm)
I had 2.73s and an automatic. slow spool(crappy turbos). lots of top speed and bad tranny slipping.
then 3.73s. no traction, less exagerated slipping untill 3rd.

new T3/T4s (powerband: 2500-5500rpm)
then swaped to a t5 manual when I blewup the auto. no traction and REdiculously close shifting, maybe a second or two between.
Then blew the pinion boosting in 3rd because it caught traction and the clutch didn't slip (GM 3.73s), so I put in richmond 3.23s, still a junk 7.5" 4th gen rear though

the powerband changed drasticly with the larger exhaust housings .48->.63, they boost way faster too.
I liked the automatic better because when I floored it, the turbos would begin to spool, then after the down shift, they'd be starting to make boost and really slingshot. Also, for easier launches. The problem with the automatic is that the 700r4 is so junk you can beef it up and still won't last long. And I gotta have overdrive.

Then the t5 clutch would slip in 4th with 3.73s and slips in 3rd with 3.23s. When I finnally get traction...the clutch lets go! I need to get a good clutch and beef up the t5, which probly = t56.

I definitely like the 3.23 gears over the 3.73s. less shifting around town, and good trap speed in 4th.

 

Ultimately depends on power level and number of bends in the ducting. The higher the power level and the more degrees of bend in the ducting the more likely you are to gain something.

Really, from the numbers you’ve posted so far, I doubt it unless you have a major mismatch in size between parts (like if the IC inlet/outlet and the TB were all 3” and you were necking down to 2.5” at each joint, even the wrong size is better then repeatedly changing size).

Spool is dependant on load, load is dependant on gearing.

That being said, probably not… as long as you’re seeing full boost or close to it by the top of first and have full boost past that you probably won’t gain anything. Really, you want to gear the car for what it runs, for example, if it’s built to run a ¼ mile then you want to be a few hundred RPM above your power peak (usually somewhere between your HP peak and redline) in your 1:1 gear as you cross the line. If that’s where you’re at with the 4.10’s, then you’ll probably slow down going with anything else, even if the 4.10’s are causing it to spool slowly.

Who says a manual is better (I’m assuming faster)?

A properly build and matched auto will always be faster down the dragstrip then a manual tranny, irrespective of induction.

With a turbo they can be dramatically faster because you can choose a converter to allow it to spool faster, use a trans brake to build more boost off the line (or even a foot brake), the engine stays as heavily loaded as it can be the whole way down the track where no matter how fast you powershift with a stick you’re still unloading things a little… the GN/TTA guys have shown this pretty dramatically, there have been a few stick cars built that were dramatically slower then the automatics. The rumor is that GM tried it also (a TTA with similar/better power then a V8 and a lighter nose would make a nice road race car) and the performance suffered so badly that they didn’t bother send them to production (that’s the rumor at least, I have no clue what tranny they would have used anyway, possibly the vette ZF which really was too expensive and too big for the chassis, the T56 wasn’t really around yet and the T5 is weak sauce).

Of course, manual shifting can help you setup the car properly when transitioning on the road course and the throttle matching that you can do with a clutch will keep from upsetting the car unless you intend it. At least that’s the argument, real world I find that on most road courses and especially autox you don’t really have a reason to shift much with an auto. Also, one of the most competitive f-body road racers here on the east coast is paralyzed and runs an auto.

Of course, you can cheat like I’m doing… 4L80E and paddle shifters

Try running a shorter, larger diameter or possibly a hard line as signal line to the wastegate, it sounds like the gate is reacting slowly to the boost signal and it’s usually something with the line connected to it. (do your data logs also show that fluctuation?)