questions about boosting my stock t-25

[96_turbo_spyder]

Hey guys I have a nice 1996 gst spyder that I just had rebuilt it currentlly has about 1700 miles I have a bone stock fuel system and my stock t-25... now when I run the car the boost guage reads a spike of about 17 psi and drops back down to about a stable 13psi, I have been reading that on stock fuel system I should not be boosting over 15... also I dont fuel cut
on the spike of 17 and I havent taken it to a seting on the boost controller to make the car fuel cut. Is this normal... or safe for my rebuilt motor??? I am new to the dsm and also this is my first turbo car I could really use your help and advise thanks

 

[drewvr4]

Will it blow your motor up, more then likely not...infact I really wouldn't worry about it

 

[absolute_DSM]

Thats what we call a boost spike in this turbo world of ours. What kind of boost controller do you have, how is it hooked up, and where is it located?

 

[96_turbo_spyder]

it is a turbonetics gold boost controller and it is hooked up with the turbo nipple on the in side and the wast gate line on the co2 side and its lokated next to the intake filter by thy coolent tank

 

[19gale2gGST]

The distance away from the wastegate and compressor could be the reason for thespike. The closer you have it mounted the less the spike should be. Keep the rubber air lines short.

 

[kenamond]

it is a turbonetics gold boost controller and it is hooked up with the turbo nipple on the in side and the wast gate line on the co2 side and its lokated next to the intake filter by thy coolent tank

Shorter is better, but I have my JoeP IL mounted on top of my rad fan shroud and spike to 16psi running 15psi boost (only spikes 1psi over). Dunno...if you have a lot of slack in your vaccuum lines, you might try shortening it. Or do an experiment putting the MBC with the shortest possible vac lines and see if it helps. But what's the "co2 side"? Did you mean "out side" but are overwhelmed by chemistry homework?

 

[96_turbo_spyder]

yes its the " out " side but on the under side of the boost controller it says in on one side and co2 on the other.... Im not very good at chemistry myself .
thanks for the info... will try shorter vac lines and see what happens... also it was happening to me with the stock bcs but it would spike 14-14.5 and hold 11
and spike again on all gears Im still on stock fuel system so I dont want to overkill with the 17psi spike. and again thanks for the info

 

[kenamond]

yes its the " out " side but on the under side of the boost controller it says in on one side and co2 on the other.... Im not very good at chemistry myself .
thanks for the info... will try shorter vac lines and see what happens... also it was happening to me with the stock bcs but it would spike 14-14.5 and hold 11
and spike again on all gears Im still on stock fuel system so I dont want to overkill with the 17psi spike. and again thanks for the info

I'd also recommend building a boost leak tester (seriously, it's not hard or expensive) and doing a boost leak test then fixing all boost leaks. I've always wondered if boost leaks could worsen spikes. But boost leaks are bad (they need an icon of something evil-looking...I'd put that here if they had one ) and should be eliminated. If you don't have a compressor, get a portable air tank (11 gallons is nice; lasts longer) and fill it whenever you need to at the local gas station. Find a way to put a cheap pressure gauge (0-30psi or so) on the boost leak tester or get an aftermarket boost gauge so you know how much pressure you put in and how fast it leaks down. Should hold 20psi and leak down 1psi every few seconds if you have no worrisome leaks. And searching will tell you much more on the details of this test. Do it, fix the leaks (I'm serious). Even if you don't have boost spikes, you should do this every oil change or every other oil change. Leaks make you run rich, rich robs power (is that a pun?), less power is bad (evil icon needed again). Okay, I'm done preaching.

 

[95autogst]

I remember with the BCS and the restricter removed that my t25 would boost to as much as 20psi then settle at around 14psi. I really wouldn't worry about the spike, above 14psi all the turbo is doing is heating the air up but not really flowing anymore. If this doesn't make sense just take a look at chemistry (haha) PV=nRT rearranged for pressure P=nRT/V to increase P with a constant V (volume) you can either increase the temperature or the number of moles (n). In the case of say 20psi it is so far our of the efficiency of the turbo that can't flow anymore air and just heats it up.

In the end- don't worry about it with a t25

 

[kenamond]

I remember with the BCS and the restricter removed that my t25 would boost to as much as 20psi then settle at around 14psi. I really wouldn't worry about the spike, above 14psi all the turbo is doing is heating the air up but not really flowing anymore. If this doesn't make sense just take a look at chemistry (haha) PV=nRT rearranged for pressure P=nRT/V to increase P with a constant V (volume) you can either increase the temperature or the number of moles (n). In the case of say 20psi it is so far our of the efficiency of the turbo that can't flow anymore air and just heats it up.

In the end- don't worry about it with a t25

Hotter means knock. Knock is bad. If it's only during spikes, that's not as bad, but it's still knock and it should still be avoided. Try shorter lines.

 

[96_turbo_spyder]

my uncle has a compressor and I have boost/vac gauge in the dash I will try the boost leek test this weekend along with the shortening of the vac lines... I do have allot of slack in the lines to the boost controller ... but I have one more question how do I get air into the turbo??? Do I need a special cupller or something of that sort the other thing that I have heard is that I am suppose to spray all the pipes with soapy water to see were the leaks are... is there any thing else I'm missing also what would be a good way to seal the leaks jb weld or another adhesive like I said earlier, I'm really new at this and its kind of overwhelming the amount of maintenance and awareness you have to have with a turbo car... but the end result is so worth the effort! thanks allot guys for all the help and keep the tips coming.

 

[96_turbo_spyder]

I remember with the BCS and the restricter removed that my t25 would boost to as much as 20psi then settle at around 14psi. I really wouldn't worry about the spike, above 14psi all the turbo is doing is heating the air up but not really flowing anymore. If this doesn't make sense just take a look at chemistry (haha) PV=nRT rearranged for pressure P=nRT/V to increase P with a constant V (volume) you can either increase the temperature or the number of moles (n). In the case of say 20psi it is so far our of the efficiency of the turbo that can't flow anymore air and just heats it up.

In the end- don't worry about it with a t25

your understanding of chemistry surprises me WTF... the force is strong with this one... . Thanks for the info.

 

[96_turbo_spyder]

Hotter means knock. Knock is bad. If it's only during spikes, that's not as bad, but it's still knock and it should still be avoided. Try shorter lines.

Ahh crud what is knock???? and why is it bad?????
I'm really confused...

 

[Black95awd]

its a t25, dont sweat it. I ran 20psi on a 16g with no fuel mods or tuning.... not saying that is was smart or right but I couldnt kill the 7 bolt. I tried!

 

[96_turbo_spyder]

thanks for the reashurence its just that this is my dailly driver and my baby... I alreddy had to rebuild it once... my wallet cant handle a second.thanks for all the advise

 

[kenamond]

If you go do a search on boost leak testing, you'll find out all you need to know. You have to make a boost leak tester. It's just a rubber coupler with a PVC endcap on one end with a tire valve through it and hose clamps on each end of the coupler. You take the intake pipe off of the compressor inlet of the turbo, put the tester on the turbo and clamp it down, apply pressure to the tire valve up to about 20psi and see if it'll hold. Chances are it won't even get up to 20psi. Then you go looking for the leaks and then fix them all and enjoy a much better-running car. That's the cliff's notes version. Go search to find out the nitty gritty details.

 

[95autogst]

Hotter means knock. Knock is bad. If it's only during spikes, that's not as bad, but it's still knock and it should still be avoided. Try shorter lines.

True, but as far as knock caused by a lean air fuel mixture he doesn't really have much to worry about.

 

[kenamond]

Ahh crud what is knock???? and why is it bad?????
I'm really confused...

Knock is when the air-fuel mix in the combustion chamber burns before it's supposed to. Normally, it starts burning at the sparkplug and grows like a bubble until everything is burned. When you knock, a bunch of the air-fuel mix burns before it's supposed to - and much more rapidly. So normally, you have a gradual increase in pressure in the cylinders (it's still happening pretty fast, mind you), but when you knock, that pressure goes up much higher and does it much more quickly. It's hard on the motor. It's kind of like dribbling a 10lb rubber ball on your tile floor...or dribbling a 10lb bowling ball on your tile floor.

Knock is caused by too much heat. If you overboost your T25, it spits out much hotter air than a larger, more efficient turbo would spit out at the same boost level. So you are more likely to knock if you push the turbo out of its efficiency range (16psi is getting out there on a T25).

You can also knock from being too lean. Leaner air-fuel mix burns hotter, and that heat doesn't vanish miraculously after the exhaust stroke. The cylinder walls, piston crown, head, valves, and spark plug are hotter. These heat up the air-fuel mix as it swirls into the combustion chamber, and they act as hot spots on the walls of the combustion chamber that can light the air-fuel mix before it's time to burn. So if you boost more which forces more air through the motor, but the stock fuel system is maxed out, you start to lean out. The one guy was telling you that this shouldn't be a problem (that you shouldn't max out the stock fuel system at the boost spike levels). But you still have to worry about knock from the hotter output of the T25 compressor.

Higher octane fuel doesn't "catch fire" at as low of a temperature as lower octane fuel. That's one way to deal with knock...and on the 1/4 mile, they use race gas with very high octane levels so that they can run much higher boost and other things I won't go into.

More than you expected or perhaps wanted, but there ya go...next time, think twice before asking me a question.

 

[95autogst]

Knock is when the air-fuel mix in the combustion chamber burns before it's supposed to. Normally, it starts burning at the sparkplug and grows like a bubble until everything is burned. When you knock, a bunch of the air-fuel mix burns before it's supposed to - and much more rapidly. So normally, you have a gradual increase in pressure in the cylinders (it's still happening pretty fast, mind you), but when you knock, that pressure goes up much higher and does it much more quickly. It's hard on the motor. It's kind of like dribbling a 10lb rubber ball on your tile floor...or dribbling a 10lb bowling ball on your tile floor.

Knock is caused by too much heat. If you overboost your T25, it spits out much hotter air than a larger, more efficient turbo would spit out at the same boost level. So you are more likely to knock if you push the turbo out of its efficiency range (16psi is getting out there on a T25).

You can also knock from being too lean. Leaner air-fuel mix burns hotter, and that heat doesn't vanish miraculously after the exhaust stroke. The cylinder walls, piston crown, head, valves, and spark plug are hotter. These heat up the air-fuel mix as it swirls into the combustion chamber, and they act as hot spots on the walls of the combustion chamber that can light the air-fuel mix before it's time to burn. So if you boost more which forces more air through the motor, but the stock fuel system is maxed out, you start to lean out. The one guy was telling you that this shouldn't be a problem (that you shouldn't max out the stock fuel system at the boost spike levels). But you still have to worry about knock from the hotter output of the T25 compressor.

Higher octane fuel doesn't "catch fire" at as low of a temperature as lower octane fuel. That's one way to deal with knock...and on the 1/4 mile, they use race gas with very high octane levels so that they can run much higher boost and other things I won't go into.

More than you expected or perhaps wanted, but there ya go...next time, think twice before asking me a question.

Good info, an explanation like that would have been great a couple years ago for me

 

[96_turbo_spyder]

I put my vac lines as short as I could and tied the boost controller t o the fan shroud .... the lines are about 4-6 inches long and I'm still spiking high so I set the boost down to about a spike of 14 and a stable 10 until I can do the boost leak test... also thanks for the info on knocking, I will try to keep my little t-25 within its efficiency range.

 

[talonalex92]

I would ditch that boost controller. Buy a new more reputable one. That ones junk. Sorry.

 

[96_turbo_spyder]

damn that just adds to the alredy big ass list.... bigger turbo...bov...fuel pump...injectors... fuel pressure regulator...F@#$ this, I'm buying a honda!....just kidding

 

[90talontsi90]

I would also subjest that you double check that your boost gauge is accurate, just hook up a little hand vacume pump to the line and make sure they read the same vacume. I had a similar issue but it turned out my cheap boost gauge wasn't reading right...

 

[96_turbo_spyder]

Ill do that but my guage is brand new from last week end.... bought it at the autozone it is a faze thanks for the insight.

 

[95autogst]

here's the MBC that I have (and a lot of other people), I've had it on the car for at least a year and it has been great.
Voodoo III MBC Manual Boost Controllers
They used to be like $15-20 on ebay... I don't know what happened to that, but at $25 its still a lot cheaper than other brands and has a good track record.