I have a 2001 2.2l cavalier. My boost fall from 10 PSI to about 7 gradually from 4600 RPM and up I was wondering If anybody has any ideas. I have volvo intercooler, Talon T25 turbo and a 2.25 inch mandrel bent exhaust and Magnaflow cat.
Thanks, Jonathan
Could be a number of things.. first check all your fittings to make sure they're tight enough, even around the intercooler.
If there is a leek on your intake side you will hear a whisteling sound (usually). If there is a leak on your exhaust side you will see carbon around the joint on the outside.
Boost leaks are significantly harder to find. You can check your vacuum hoses, or better yet just replace them all and make sure they're routed correctly. Leaks in hard piping can be very difficult to spot, and any boost leak is hard to pin down with any accuracy because there are so many lines and pipes that carry pressure. If you don't want to replace your hoses a soapy water test could work, but it's not exactly the best method. Good luck. I'd recommend checking the injector seals, especially if you've touched the fuel rail/injectors/intake manifold in any way.
Or purchase a leak tester?
Well I had this same problem before when I had my old intercooler piping using regular bent exhaust pipe but now I have mandrel bent piping and it is connected using T Bolt clamps and the problem is still the same, I was thinking more along the lines of a flow limitation somewhere but keep on firing ideas my way.
It's not a crack in the piping, it's a leak in the seals, somewhere when the vehicle hits boost. The fittings probably aren't tight enough, and the boost leaks out under heavy acceleration.
When I discussed intake/exhaust side leaks, I wasn't just talking about the intercooler.. check the fittings around the turbo it's self.. and even check the exhaust piping for cracks, rust spots, loose connections, etc.
If your using a manual boost controller there's a good chance that it's that. Seems to be inherent nature of a MBC. EBC's don't have the same PSI drop problem.
Sounds like your getting out of your efficiency with that turbo.
T25 is well within it's efficiency at 10 PSI... Stock they're set to 15, I believe. Tired a leak test yet? Or looked for any signs?
What do you mean a leak test. I am confident the motor is good it was just bored 20 over and fitted with eagle rods, weisco pistons and file to fit rings and a victor reinz head gasket and ARP studs. what could leak?
Quote:
z2Four
Saturday, July 23, 2005 10:36 AM
T25 is well within it's efficiency at 10 PSI... Stock they're set to 15, I believe
no, they're not.
boost isn't the important factor, its pressure ratio, as well as the displacement and volumetric efficiency of the engine in question.
For example, assuming an 85% efficiency rating for the OHV (a little over zealous, however I have a ported head which is why I assumed this for my calculations) injest the following:
Boost: 10psi
My pressure ratio would be 1.78
and my CFM (corrected mass flow rate) for each RPM is as follows
RPM (CMF) lbs/min
3000 14.67
3500 17.11
4000 19.56
4500 22.00
5000 24.45
5500 26.90
6000 29.35
if you look at this T25 compressor map I found (even in 60 trim) your CMF is WAYYYYYY off the efficiency range of the turbo, dropping boost and losing power.
the pressure ratio (boost) is 1.78 for 10psi... peak effeciency for the T25 is 1.4 to 1.7 so you're just above the peak efficiency of the turbo. Then, the CMF (corrected mass flow) of the engine is at the edge of the efficiency by 20 lbs/min (roughly 4000rpm) and completely off the plot altogether by 25 (5000rpm) which is why you run out of boost in the top end.
as was previously said, your turbo is the problem, its too small for your application.
Upgrade to the T3 super 60 if you want awesome power with good spool.
check this out if you want to match your engine to any turbo so long as you have a compressor map it has an easy to follow step by step how-to
The perfect turbo match
so you can understand a bit better.... the green is the peak efficiency of the turbo...
the red line is 10psi of boost on the 2.2 OHV engine assuming 85 percent efficiency
and the X's mark the CMf rates on the Pr line... as you can see this turbo is TOO SMALL
you're hardly on the plot at all
holy hell.... you know your @!#$.
You know PJ , i love you buddy. But sometimes i just cant comprehend what your writing
.
But its time to upgrade that turbo Jonathan!
Quote:
rob
Yesterday 4:48 AM
holy hell.... you know your @!#$.
not always, but compressor matching is one of my specialities
