I actually taped the wastegate discharges closed, and drove the car easy, and inadvertently hit 25 psi for a second and pulled my foot back, tape was still on the wastegate tubes so they aren't opening. And the video I posted above is with the rocker arms all backed off, turbo air inlets capped off, and feeding 10 psi regulated shop air into the fitting on the compressor discharge, only leak I found is the throttle shafts on the 3 month old Holley. They were supposed to send me a call tag this morning, still haven't gotten it. Old turbos are long gone, I took that all off 3.5 years ago when I pulled the car apart to redo it.

 

I'm a marine mechanic by trade, do alot of cat/ Cummins work, so my hands Never get a break unfortunately. Engine doesn't run a pvc system, all vented through breathers on the valve covers. Only thing I noticed is that the engine doesn't rpm like it used too, this thing used to rev like crazy, if u manually shifted it, and locked out electric shift control, it would easily go over 7200+, now it feels lazy, that's really the only thing I notice about it. As far as driving around, the engine itself runs great, plenty of low end torque, decent mileage, and does well. Doesn't use any oil, and has almost no blowby. I feel like im missing something, but I'm kinda like I've covered all the bases. Only thing left is ignition, but I did cap, rotor, wires, new coil, new ignition pickup, but there is no evidence of misfiring.

 

hmm any chance the converter (is it auto) is letting go? I've never had it happen so I don't know the symptoms besides I know the car gets slow

 

I'm not sure, the car seems to drive normal, and shift normal. Transmission fluid color looks normal

 

Double checked the balancer marks when you checked the cam timing I assume?

 

nvm, you said you increased timing in 2* steps until strap was marked....

I'm still stuck on one of the turbos not carrying it's weight.

 

At what rpm did it hit 25 psi? Did it still need 5,800 to hit 14 psi? (with the WGs taped shut) If boost comes on quickly after 5,800 some things are working OK. Do the new heads flow better than the old ones on the exhaust side? Can you advance the cam 10*?

If all else fails those 0.96 housings are too big.

I don't suppose you could post dyno charts (and boost) before and after?

 

Yes, verified the timing marks

 

Pull the compressor housings on the turbos and see if there are any witness marks on them, check free play and so on. I also think one of the turbo's just isn't pulling its weight, although I would have expected higher IAT with just one turbo compressing.

One time I lost a tape measure during a build, couldn't figure out for the life of me where the tape measure went, then I wasn't building boost. Tape measure went in the up pipe and melted, the tape survived and got tangled in the exhaust wheel.

 

yeah I went home and thought about this for a minute and wanted to come back and say the same thing, I think its time to inspect the turbo(s), check the shaft play, make sure they spin freely and no contact. Then examine their speeds/behavior with the engine running. Listen for strange noise. You should be able to feel something wrong if there is..

 

Are those turbos the S300 clones that have the goofy turbine wheel design?

Mentioned a bit here: https://www.theturboforums.com/threads/spooling-twin-vsracing-billet-78-75s.385098/

 

Do any of you guys know Holley EFI if I post the gcf file? I buddy of mine looked at it today and didn't feel that it was correct. I payed a tuner to do it on the dyno.

 

Downpipe size, wow what a difference!
Discussion in 'Turbo Tech Questions' started by turbotbirds, Oct 1, 2009. Interesting read right here on the turbo forums, don't know but maybe it will help , since he had similar problems, and the picture of his downpipe has a sharp 90 right off the turbine and is 4'' open

 

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turbotbirds on this site had problems spooling with this 90 degree bend right off the turbine style downpipe on his 355. Its an interesting read , i tried to send a link The thread is called downpipe size, wow what a difference. He still runs a sbc nowadays and is turbojohn on youtube

 

you can see on the left one of the downpipes, basically it's a 3" pipe with a gentle 90° bend, the stock exhaust tees into it, and at the bottom of the 3" pipe has an electric cutout that is open.

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One thing I see by looking at what the tuner did, and how the holley took the inputted info, the engine only has 34° of timing when it starts to transition to boost. My old setup in the msd had 38° in cruise, and 38 before the Transition, and didn't pull any timing until it hit 4 psi. I don't know if this is enough to cause a problem though.

 

I don't have your whole combination in front of me, I remember you are using high octane fuel.

I wish to give you an idea of the sort of pump gas timing numbers we generally use for the sake of discussion.
Most V8 engines 9:1 modern CC using 93 octane and 15psi of boost typically wish to keep EGT below 1300*F (pre-turbine) and use less than 15-16* of timing btdc, from say 4400 to 5800rpm, with a slight dip through peak torque.

Anything over 18* is unreasonable in those applications for a variety of reasons.
In forced induction application you should not be using a lot of timing. Unless the fuel was absolutely slow (very high octane) and even then I wouldn't push 30+ lol. More like 24-26 max, and I would start with 18-20* , and walk it up and down using a dynometer not the plugs.
For another example, around 3300rpm and 15psi I am using roughly 2* of timing in some engines.
I know of a 122 cubic inch motor that makes 500ft*lbs by roughly 4k and the timing is about -2* at 30psi, with 93 octane solo, yeah.

I'm not sure how dependable the plug strap marks are when using high quality fuels. You are much more likely to catch an timing issue by starting with low boost and using a dynometer.

 

This is a 23° SBC. They like lots of timing. 14° at 14psi is safe pump gas timing for a LS with their fast burn heads. Not on a conventional SBC. It would be a dog with those numbers.

 

I did qualify the combustion chamber as having to be modern in my post.
I agree there can be a substantial difference in spark timing given the older tech chambers.

nice catch/comment.

Nevertheless the technique I outline (using dynometer and gradual boost adjustments) would still work. And I would still start somewhere near 18-20* just for the whole picture, since its relatively safe if you know what you are doing (don't run the engine to redline, care for the EGT, pay close attention to torque vs boost)

 

What Bad Medicine said.
Call it archaic, even 18 deg is on the verge of hurting parts in a conventional sbc. Its seriously still completing combustion in the headers at that timing.
My personal experience , I wont start under 25 on this type motor. If it shows detonation, the inlet temp is too hot, and it needs to be addressed.
This might blow your mind, but when these engines are run at or below ambient inlet temps under boost, they make best power at or near naturally asp timing.