MCharbe

Guys, this is my dyno results. I have a question, boost seems to oscillate and slowly goes down with RPM. Is that normal? I have a Lindsey Racing MBC and dual port wastegate.

Paulyy

If you have a k26/8 then yeah, the turbo is at maximum efficiency and cannot pull in any more air,

Willard Bridgham 3

K26/6 has the same problem

rlm328

Get a better turbo

Josh B

Looks great to me - full boost at 3000 rpm. Lots of usable power - nice torque curve. 300rwph at 15lbs in one of these cars is very respectable IMHO. The A/F curve looks good too.

Laust Pedersen

The slight drop-off in boost is typical for a manual boost controller and can be explained by increasing back (exhaust) pressure pushing on the waste gate valve.
The wiggly boost curve is not reflected on the torque curve, which could point to a test rather than a controller or turbo issue.

Overall everything looks good.

But if you need a head-scratching issue, then: Why is the "knee" on the boost and torque curves offset by 200 rpm?
Btw, what turbocharger are you using?

Laust

Dave W.

Keep the vac lines between the wastegate and boost controller short and avoid large diameter hoses. I've seen boost oscillations with large/long hoses since it takes a little time for them to pressurize/depressurize.

MCharbe

Thanks for your comments guys. True that the boost oscillation is not reflected in the HP curve, so it might be an artifact of the external boost measuring device we were using. But anyways, I have decided to try a boost solenoid, which is supported by VEMS, and install it under the hood where the cyclic valve was (I currently have my MBC in the glove box, lengthy vacuum hose..). FYI, my setup is:

- Stroker with a 968 crank and cylinders bored to 101mm
- VEMS
- 3.0 bar fpr
- 80# injectors
- Manual Boost controller set at around 15psi
- 3 inch exhaust with cat delete
- Lindsey Racing dual port wastegate

And yes, not the most powerful but it's plenty for me, my car is fun! :-)

Mathieu

Smudo

What kind of turbo do you have? Still OEM k26/6? I also have vems and use salenoid valve for controlling the boost. Works well for me.

MCharbe

Yeah, I guess I forgot this important information! It's a k26/8, my car is a 1988 turbo S.

Raceboy

Mathieu, seems that K26/8 is too small for a stroker. Its compressor is not the latest design and boost is dropping because it cannot keep up with the engine needs. Can be compensated a bit with EBC.