My Drag Slip 8-13-04 [Archive] - SaabCentral Forums

: My Drag Slip 8-13-04


Clint
16th August 2004, 12:03 AM
I went to the track Friday night with intentions of running a tenth or 2 faster than last month(14.99). I have put a Jt 3" turbo back exhaust on since then. I also removed my mbc because I have noticed a lack of power at top end with it on, even with the exhaust.

I am having trouble posting the picture, so here are the main #s:
60ft : 2.261
1/8 : 9.500
1/4 : 14.556
MPH : 98.96

I was only at 92mph with the mbc on in last months run. The air was also alot cooler and dryer this month, so some of the loss in time is because of that. My friend in his camaro(left lane on the slip) ran 2 tenths faster than last month because of the air conditions.

So if you have an mbc, you can see that you arent actually faster in a drag race with it. I really dont see an mbc good for anything but crusing around town in 2nd gear because of the torque rush. You might think that it will get you a better 60ft time( I did), but my 60ft with it on was 2.924 last month. Cleary, an mbc is not a good upgrade. Especially after you factor in the abuse to your engine and tranny.

bkrell
16th August 2004, 12:21 AM
Cleary, an mbc is not a good upgrade. Especially after you factor in the abuse to your engine and tranny.

No offense, but how is an MBC any more abusive than an ECU upgrade. And...drag racing? :o

Besides, it's not all about drag racing...

Anyway,I hold boost pretty well but I have the +A with the boost tap up by the throttle.

Try one of those at the next drag race.

ricot83
16th August 2004, 10:49 AM
i have my mbc installed in series, since i have t7 so i actually get more boost on top end.... and i love drag racing but id rather road race this car than drag it... in octobre i will go drag it at the track so we will see what the hell i can muster out

Clint
16th August 2004, 10:57 PM
Cleary, an mbc is not a good upgrade. Especially after you factor in the abuse to your engine and tranny.

No offense, but how is an MBC any more abusive than an ECU upgrade. And...drag racing? :o

Besides, it's not all about drag racing...

Anyway,I hold boost pretty well but I have the +A with the boost tap up by the throttle.

Try one of those at the next drag race.

I am not saying that it is all about the 1/4 mile, it is just a good way to see improvements without access to a dyno every month. I actually prefer road racing.

I was actually planning on trying the +a mbc next time I go to the track. How is it you have the boost tap by the throttle?

An mbc is more dangerous to your engine than an ecu upgrade because with an upgrade you have different fuel maps, with an mbc you are going to run lean without some fuel system mods.

Stalker
16th August 2004, 11:56 PM
with an mbc you are going to run lean without some fuel system mods.

Not exactly true. With a stock t-5 fuel system, it can map fuel up to the 17psi range. The fuel cuts occur at 15.5psi, so there is about a 1.5 psi buffer range if you will. Yes, the ecu is safer than the mbc since it does map more fuel along with the boost increase. Odd that the mbc showed no improvement from stock on the drag slip.:-?? The anticipator mod allowing you to tap boost from the throttle body gives you boost that comes on stronger and holds better in the high rpm ranges. The colder air will make a huge difference in performance of the t-5s. I havent seen a dyno of stock vs mbc, but im sure the mbc would give some hp. The tb tap should help with the top end dying out though.

Cheers,
Stalker

bkrell
17th August 2004, 07:53 AM
You can actually move the tap for the MBC to the throttle body w/o usning the +A setup. I believe ERP has a pic somewhere. However, once the cold sets in, you'll see stronger spikes from that location. That's where the APR comes in. I was noticing my boost seemed to be lagging a bit back in June or July. Per discussion w/ SPATL, I closed off the APR completely while the wether is hot. I still get high, sustained boost thanks to the TB tap. When things cool back down a little bit more than the odd freakish weather has already done, I will probably start bouncing off the fuel cut again and have to open up the APR again.

SPATL
17th August 2004, 09:41 AM
I was actually planning on trying the +a mbc next time I go to the track. How is it you have the boost tap by the throttle?

An mbc is more dangerous to your engine than an ecu upgrade because with an upgrade you have different fuel maps, with an mbc you are going to run lean without some fuel system mods.

Within the limits of the stock ecu induced fuel cut a t-5 will not lean out unless something else on the car is bad. While an ECU upgrade should provide better fuel mapping which should by virture of that be a safer thing, ecu companies have also messed up from time to time and set their ecu incorrectly causing improper a/f ratios causing the car to run lean as well.

I don't know your car or mods but I am guessing that it is a t-5. Your comparisons have too many variables and the addition of the 3' exhaust plays an important role in it as well. Some have found that their car was less responsive with the 3' exhaust. How about IC?, how about BPV? how about ambiant temperature/(Although you did mention that) how about driver's ability? some days are good and some days aren't.

The use of an MBC should improve your drag time because you won't have the ecu induced turbo lag and therefore be quicker off the line. Next you'll be up against the flow limitations of you IC. If the MBC is tapped at the turbo, you will experience boost droop because the turbo will run out of steam. Moving your pressure tap downstream of the IC will allow for longer sustained boost at higher rpms which would be what you are looking for on the 1/4 mile as well as quicker spool up.

The best place I have found to tap boost is between the TB and the IAC. While it is not the perfect place, it is a good place. Off boost at idle the IAC is opne and functions properly, on boost the iac is closed and the pressure can be used to drive the MBC. So half way down the 1/4, you should be able to hold boost the entire time without droop or taper until the flow limitations of the IC is reached. Heat AND Humidity will affect flow which will effect times.

The last thing is the MBC. Some MBC's are more porne to spiking than others. A MBC with a range of 0-30psi will be more prone to spiking than a MBC that is rated 0-20psi. The Dawes style MBC is rated 0-20 but in reality might only be 0-17. That syle MBC is ideal for most folks who are running within the stock fuel cut.It is a very responsive MBC with the least amount of overshoots I have tried in MBC's (and I have tried a bunch. It might not be the best one for folks who are above that boost level as it may run out of it ability to stay closed. There are modifications you can do the the Dawes style MBC to increase the range by placing a small washer inside the valve but the flip side is more pressure spikes. But that is where the apr can come in to help with that.

Hopefully within a the next couple of weeks I will have a dyno sheet to see how the MBC+A looks on paper.

Clint
17th August 2004, 10:03 AM
Mods:

JT turbo back
3" intake to the turbo with filter behind fog light
Apexi BOV ( I am still using bosch bov too)
Viggen Intercooler
and a handful of little things.

All I know is with the temp. down about 15 degrees, the humidity way down, and the boost controller off I cut 45 hundreths off of my time. before with the boost tap at bthe turbo it would hold boost at 12psi. that means 12 in all gears compared to the 5 in first and 8 in second. I still had a better 60ft time without the mbc. I will try the +a with a boost tap at the throttle body and let you know how it turns out. That is if i dont get my cams in my car before next month. If I have those in, I wont be able to tell which set up works best unless i try them all again, which might happen anyway.

What is the APR? what is the IAC?

bkrell
17th August 2004, 10:05 AM
Air pressure regulator and Idle air control. Research the MBC+A threads. It'll fill you in.

toenail
17th August 2004, 04:15 PM
Clint- Given your listed mods you should be capable of almost instant 15 psi in all 5 gears with a MBC+A tapped at the throttle body. Your biggest obstacle at that point will be wheelspin in 1st and 2nd. This CAN increase your 60' times thereby increasing your ET for the 1/4. It takes a bunch of skill to master rolling into the throttle just right to maximize acceleration.

Drag racing aside I still chuckle everytime I leave an intersection with 15 non-tapering psi on tap. Much fun.