Here's my set up.
357 Windsor, 8.5:1, custom cammotion turbo cam, Canfield avenger stg3 heads, victor Jr. Intake, Holley 750 built by Brent Davis (crutch). Twin t-70 turbos with .68 ex housings. Fully built 4r70w trans 3.27 gears, 275/69/15 MT dr's.

Same me setup I've had for a long time except I upgraded the old 57mm turbos to twin t-70s. Also swapped my old race c4 for the 4r70w. I've only had it out for a few weeks. Have NOT went WOT yet, my wide band died and I haven't installed my new one. Anyway when I get to 2700-3000 rpm the turbos start bleeding off, sounds like a bov but it's coming from the turbos and it alternates from the drivers side to the pass side. Very wierd.. My old turbos never did this. I do have small filters on them I wonder if they are choking the turbos? It's almost like they are to the point of making boost but not quite and they start popping off... And one else have this happen?? Did a burnout in 1st gear and it didn't do this just when I shifted into 2nd gear it started chirping.. It's got plenty of power.. Feels like it just wants to go WOT,,, At 55 mph in 3rd gear half to 3/4 throttle its hauling ass but still "chirping" the boost gauge bounces from 5-10 psi..


Turbos too big?

 

I was going to say compressor surge. Anti surge compressor housings? May have to switch to some larger a/r turbine housings or smaller compressors...

 

Just normal compressor housings. So you think they are spoiling too fast?

 

Its possible with that much compressor. Larger a/r will allow it to spool later when engine is using more air, and keep compressors out of surge.

 

Damn Im really hoping these will work. Prly a dumb question but will more timing help? Right now I just run a msd 6al box with the distributor locked at 22. Getting ready to install my 6al btm box and run like 38degrees pulling 1 degree per lb of boost. I run 15psi..

 

I agree that its compressor surge. Seems like you are driving the turbos too hard at the lower rpm. Does the chirping go away as rpm gets higher or if you lift off a little?

Twin 70's will move alot of air and if the pr goes too high at low rpm/air consumption, you will be on the left side of a surge line on the map.

 

It really doesn't go away. When I did a burnout they were singing nicely.. As long as I shift at super low rpm you don't really hear it, mostly in 3rd driving it hard.

 

You might ask Marty, I remember him having the same problem with his firebird, I just don't remember how he fixed it.

 

Can u point me in the right direction, I don't know who marty is. Thanks

 

TRBO355 with the grenade. The surge issue was talked about in the grenade thread iirc.

 

It's compressor surge. When I tried .68's for turbines on my 388 it did that going up a small hill. No issue when I put the .96's back on.

 

.68. I wonder if .81 would do the trick? .96 seems like they would be laggy as hell. How does yours spool?

 

I dont think I would jump to a .96 but I havent ever made that kind of change so dont know for sure.

 

Not much lag at all on my setup with the .96's but I run e85 which makes more exhaust. On yours .81 would probably be a good jump with the gas.

 

I wonder if .81 would fix it or do I need to sell these and buy a pair of 61's...?

 

I took out the bov spring and cut two coils off of it so it would just hang open at idle. That helped my problem but didn't fix it. I'm surprised how much air these 70's move at idle. Then took off my air filters and went for a drive. All I could hear is sweet turbo spool no more surging.... looks like these filters were choking my turbos. They are small but I don't have a lot of room, with the compressor housings being in the inner fenders. Never thought that would be the fix, lol. My bov is MUCH more responsive now, I could barley hear it before

Jeremy

 

That makes sense. So are you just going to run without filters?

 

Just for a drive.. I need to come up with something