Intake mod performance

[gorf]

This is my first post. I have been able to answer all of my previous questions through searches.

I am working on my second Spyder GST, the first one just was not in good enough condition to put a lot of $ into. On my first GST I added an EBay cast aluminum intake. The results were what I expected; it seemed to pull harder through the whole power band.

My current GST, after reading all of tech tips, I decided on a 4" K&N style filter and to mod the stock intake by cutting the BOV pipe. The results of this are a little confusing to me and I was hoping for some feedback. Before installing when I hit 3000 rpm my turbo felt like it was fully spooled and would pull consistent up to redline. AFTER installing the 4 inch filter and cutting the pipe, I hit 3000 and it pulls a little harder than it did, but when I hit 4000 it feels like I hit the after burner and starts pulling a LOT harder. Is this common? I was expecting to hit 3000 and just pull harder.


Second part of this is that when I come up to a light from a cruise and push in the clutch, the engine idle drops down to about 200 rpm and will sometime die. It did not do this before. Any ideas?

 

[big_eskimo]

My current GST, after reading all of tech tips, I decided on a 4" K&N style filter and to mod the stock intake by cutting the BOV pipe. The results of this are a little confusing to me and I was hoping for some feedback. Before installing when I hit 3000 rpm my turbo felt like it was fully spooled and would pull consistent up to redline. AFTER installing the 4 inch filter and cutting the pipe, I hit 3000 and it pulls a little harder than it did, but when I hit 4000 it feels like I hit the after burner and starts pulling a LOT harder. Is this common? I was expecting to hit 3000 and just pull harder.

What do you mean you 'cut' the stock intake by cutting the BOV pipe? You mean you cut the recirculation hose from the BOV? This is not a good idea and is probably the culprit with the way your DSM is running. If you want to safely vent you need to get a MAFT setup. Hope this helps.

 

[MrBoxx]

He probably means the dump tube that extends inside the intake pipe. Cutting this is a fairly common "free" mod to free up the flow of air pre-turbo.

gorf, do you have an aftermarket boost gauge? If so, what is it reading and how long is it taking to get to max boost? Do a boost leak test and check for exhaust leaks where the engine/manifold and turbo/manifold meet. It seems to me the T25 should be spooling a bit faster, but without a little more info, you never know.

Regarding your rpm drop problem... sometimes (and since someone on here will no doubt say that it's overrated and too many people worry about it too much, I stress the "sometimes") crankwalk can cause rpm's to drop when the clutch is pushed in. I would check that, even regardless of any problems, it's a good thing to know if it's starting to happen. But I doubt that's the problem. If you actually did cut the BOV recirc tube, that could cause a problem. When you say it didn't do this before, do you mean before you put the intake on and cut the dump tube, or before as in it's a new problem that cropped up without modifying anything?

 

[gorf]

Yes you are correct I cut the dump tube - the free upgrade. On my first GST I used a cast aluminum intake pipe, on a scale of one to ten I say it added a two. On this car with the dump tube cut and a 4 inch filter I would give it 3 - much more power then the aluminum casting.

I have not added a Boost gauge yet - it is on order, hope to have it by next w/e. Before I put the filter on and cut the tube, I was at max boost by 3k. But now it feels like it did at 3k but at 4k it kicks even harder. I'll check with good boost gauge when I get it.

The RPM issue did not exist before cutting the dump tube and adding a larger filter.

I have done a lot of reading about crank walk and the best I can tell it goes something like this" it might do this or might do that but then again maybe this...." Followed by "you either have it or you don't". Any good clear indications of crank walk?

 

[MrBoxx]

Yeah, the usual symptoms are throwing belts off the pulleys since the crank pulley is moving too far, the ticking of the crank angle sensor getting chipped away by the crank, a dropping clutch pedal or no clutch pedal pressure on hard left-turns, and sometimes, a drop in RPM when the clutch is in. That's the only reason I threw that out, though. I doubt you have CW. Put it this way: I was told by the Mitsubishi dealership that my car had it, and I show NO symptoms whatsoever of crankwalk. The only thing they said was that they could see the crank move when they pushed the clutch pedal. Soon, I'll do my own measurements and check how much play there is, but for now, the engine is running pretty damn strong. (knock wood)

There are a ton of things that can affect idle, though. Most are throttle body related, and I admit I'm not the most qualified to answer questions about that particular part. But I am learning, little by little. Hopefully someone else more knowledgeable comes in and sheds a little light on that. Sorry if I couldn't help any more, though. I can't see anything from a filter and a dump tube cut that could affect it, unless something in the MAS got affected. Perhaps the plug isn't on all the way? Are all the honeycombs in it?

 

[treefrog1112]

my car's the same way, 4k rpms and its after burner time. just a few more mods than you.... i always thought it just starts to hit the good part of the power band.

 

[gorf]

Thanks, I just thought 4 k was too high considering before nay mods it felt like it was fully spooled at 3k. But I have been driving for a couple days and that is correct - it really comes on at 4k.
I think the RPM issue ONLY happens when I am slowing down from high speed and the turbo/engine is hot. Any other time it is fine.
Recieved my boost gauge plan on putting it on the w/e, how many PSI is normal; for a stock t25?

 

[MrBoxx]

Between 10 and 12 is normal. Sometimes after adding a few parts like intake and exhaust, boost might go up a few psi. The stock BOV will probably start leaking after around 12 anyway, which will limit how high boost goes. Switching to an aftermarket or 1g BOV solves the problem. As always, do boost leak checks to make sure you're not leaking anywhere else.

 

[ArcaineGST]

hmm...... 10-12. After I had only an intake and bov I was pushin 14-16. And now after my full exhaust I can hit 18 max. That's funny. GT25/40R here I come!!!!!

 

[joosdawg]

arcaineGST looks like you live 5min from me, need some help with your car? . When i had my 2G and i put a 3" turboback, intake, hardpipes and the stock BCS i only hit 13psi max. Ahh the T25 days...warf

 

[gorf]

Just a quick update. Since I first posted this I have added a boost gauge, Dave Brode UICP with 1G BOV and a full turbo-back exhaust.

Checking the boost gauge, the assumption was correct, at 3000 rpm the boost starts in but at 4000 rpm it is at max. With just the intake mod I was only able to get 10-11 lbs boost. I Tried a MBC and still was only able to get 10-11, so I did not use te MBC. I changed the UICP and BOV and without a MBC I am seeing 14-15 lbs boost. Made a HUGE difference in HP!

I then installed a 3 inch turboback exhaust, it added more responsiveness but not as much HP as the UICP. As far as what the boost gauge says it reads about the same unless I spin my wheels then it seems to spike up to about 18 before setling back down. This maybe just my gauge - not sure.