Slow to spool

[onspeed]

'87 Turbo spooling a bit slow. Has been on going issue, just now having time to try to address it fully. Some amount of trial/error over the past few years. 2.5L block, top end refreshed with new head gasket. Older vitesse MAF + PB kit. Has a aftermarket 3" exhaust from the downpipe back. New K27/6 "Raptor" Turbo from Evergreen. New vacuum lines. New wastegate. New headers (granted their Ebay OBX brand from a few years ago when you could purchase em).

Not getting full boost 15-16PSI until 3.6-3.8k RPM or so in 4th gear. Per Charlie @ Evergreen, the turbo should be doing that 2800 or so. Replaced a Vitesse stage 2 that was on the car when I bought it that I thought might have been the problem, but really performance is about the same.

Pressurized the intake system at the intercooler inlet. Very small leak on the intake manifold fittings for both the banjo bolt screw insert, and the hose barb for line to the brake booster, not audible but can see some bubbles when I spray it with soapy water. Going to try slathering both with some JB weld once I have a sec to pull the intake again. But overall they're quite small and I don't think would be causing such a pronounced spool problem.

Kind of at a loss, must be on the exhaust side? Turbo crossover pipe? - did not see any cracks on it when I had it off for the turbo, didn't look crushed internally, at least looking in from the flanges.

Unrelated - if anyone has a batwing for the front bumper I'm looking for one. And now have a vitesse stage 2 turbo to sell - probably will send to evergreen to have seals replaced.

[Tom]

Welcome to Carpokes! What are you using for boost control, and what wastegate do you have? Do you have a wideband to confirm AFR under boost? Assuming no intake or exhaust leaks, I'd be inclined to look closely at the wastegate and how you are controlling it. Many (most? all?) factory wastegates are worn out at this point (weak spring, leaky valve), and can produce very lazy boost curves like that. You can shim them and/or try to mask that with boost control tricks (Lindsey boost enhancer, banjo bolt restrictors, electronic boost control settings, etc.) but ultimately a new Tial wastegate is the best solution in my opinion -- if the wastegate is the cause of your issue. Could be lots of things of course, but your post would seem to eliminate some of the other likely causes. I also don't know that turbo so can't say when it should make full boost, but every Vitesse turbo I've used or experienced can hit 1 bar by or before 3k rpm's.

[gruhsy]

Slow to build boost usually is the bypass valve has failed.

Test drove a car once and that was the exact symptom.

[Tom]

Slow to build boost usually is the bypass valve has failed.

Test drove a car once and that was the exact symptom.

Good call. Also on the short list for sure.

[onspeed]

WG is a Tial 38mm with a MBC.

Bypass valve is an APR R1 unit. If it was failed I would think it would not have held pressure when I pressurized the intercooler?

Lambda is like 0.8 at WOT on boost on the WBO2.

I thinking either tune/piggyback problems such as excessive timing retard? or an exhaust issue?

Might just have to pull everything off and buy one of these jigs to pressure test for leak: https://944online.com/pressure-test-kit-pre-turbo.html - anyone have this kit they would be willing to loan? Suppose I could fish a borescope through it to make sure the inside isn't collapsed..

[notny41]

That pressure test kit does not look like a fun thing to fit...

Is there any way to test a bypass valve?

[Tom]

WG is a Tial 38mm with a MBC.

Bypass valve is an APR R1 unit. If it was failed I would think it would not have held pressure when I pressurized the intercooler?

Lambda is like 0.8 at WOT on boost on the WBO2.

I thinking either tune/piggyback problems such as excessive timing retard? or an exhaust issue?

Might just have to pull everything off and buy one of these jigs to pressure test for leak: https://944online.com/pressure-test-kit-pre-turbo.html - anyone have this kit they would be willing to loan? Suppose I could fish a borescope through it to make sure the inside isn't collapsed..

If you are running Vitesse software without big piggyback timing changes, that's probably not it. Lambda of .8 (AFR of 11.76) is good too, which suggests you don't have a big boost leak. Maybe some smaller leaks, so worth checking if you haven't lately, but odds are that's not it.

I went back to the stock bypass valve after having an aftermarket valve stick on me (Forge). Not sure about your pressure test, but it's easy enough to pull out and test visually with a MityVac. In my case, it 'held' vacuum, but the piston would get cockeyed and stick in a random spot. The result was slow spooling, but also sluggish power once the boost spooled up.

What MBC are you using? Some are sloppy. Did it previously spool better and just start doing this, or has it always been like this? Sure the Tial and MBC are plumed correctly? Excessive back pressure from clogged cats and collapsed downpipes are known to produce slow boost, but sounds like you've replaced all that. Any signs of exhaust leaks (black soot) between the head and the turbo? Not recommending it, but I once blocked off the wastegate port with a sheet of copper cut to the shape of the gasket (with no opening), to see if the problem was in the boost control system or elsewhere. Just have to be super careful not to let the boost climb too high.

What is your vacuum at idle (~840) when warm?

Is this happening in all gears?

[Spencan]

I have a very similar setup, I have an EBC instead of the MBC, and the same problem. I am interested to see what you find and how you find it. In the meantime, I'll be checking my wastegate and connecting pipes.

[333pg333]

Not sure what MBC you have but many years back I had one from LR and it would fill with dry powdery burnt oil. We didn't know it at the time. Eventually we checked inside and cleaned it out. Car ran much better afterwards. Possibly a long shot but worth looking at.

[onspeed]

Have owned the car for almost 10 years now. Purchased off someone I knew on RL. Kind of always been slow to boost like that. I actually found an old thread I made on RL about this issue from back then that I forgot I even made. Have thrown various parts at it over the years but overall didn't drive it much, probably put less than 10k miles in that time period.

Prior to that had a '86 turbo with initially the stock K26 w/ APE chips, then eventually upgraded to a T3/T04E turbo with one of Rogue's early M-Tune builds, like around 2010, before he sold it to LR. So I have a frame of reference for what the boost should be like.

MBC is a LR unit. Was on the car when I bought it. Pretty sure it's routed correctly with the wastegate. I'll take a peek at it again tonight. But the MBC works, and if I recall if the ports are flipped on the Tial you get overboost. And seems easy enough to take it apart,maybe I'll do that. I think it's a 0.8 bar spring so maybe I'll try to run a straight line from the IC pipe to the WG and see if it boosts to 12psi any faster with the MBC out of the picture.

The bypass valve is actually a new unit. It had a different aftermarket one on the car when I purchased it. I guess I could have two bad ones but what are the odds. With the outlet of the valve disconnected from the MAF pipe, and the intake system is charged to 15-20 PSI, there's no leaks out of it.

Vacuum at idle is only 15 mmHg. Always thought it seemed a bit low. I remember being closer to 17-20 on the last car. But no significant leaks when the system is pressurized. Engine has 105k... could be low compression? It runs smoothly, and once it's in boost doesn't seem significantly down on power to my butt dyno .