349 RWHP and 410 RWT, Hits about 9.5 lbs @ 2700 and starts to fall @4300 down to 7 lbs. by 5000. Dyno Tech said I would be down on HP too at only 7# @ 5000 with the low compression. I will throw up the dyno sheet next, why is the boost falling off?


I thought this combo would make 70 more @ the wheels..Heres what I got...306 DSS o-ringed SB w/ low compression pistons (8.5:1), Main girdle, stock rods and crank balanced w/ARP fasteners, Edelbrock Performer 5.0 heads w 2.02 in., Bullit racing cams custom grind @ 222in. 218 ex. 115 LSA .544 lift, Holley Systemax intake, 60# injectors, 75mm TB, 85mm Meter, 38mm wastegate w .6 bar spring

 

Heres the Dyno Sheet and a pic of the setup.

 

had to resize

 

Am I just missing where it says what turbo you have?

 

61mm precision set @ .6 bar (8.8 psi) Cartech kit with mods and its a 38mm tial WG

 

What about plug gap? Running .034 now but from the looks of some of the other post I should close that up a bit even though I do not have any signs of the spark blowing out (missing or bucking at high RPM). Runs smooth up to 5500, just stops making power!


Any suggestions

 

What size exhaust housing does it have as well what kind of tiiming do you have in it when it looses power

 

306"?

 

Yeah, what c.i.

john

 

The odd thing to me is you have pretty much a 9psi wastegate spring and it's going lower than the springs rate??

The spike makes sense with a larger cube motor at such a low psi, but not falling below the springs rate. I'm sure you're not using a boost controller so I'd try another spring to see if it will hold the rated psi.

 

Yea, its a 306. I had what seemed to be valve or lifter noise so I pulled the intake and valve covers to check my preload and it was dead on all the valves. I did find one problem though, on the dyno it had been blowing oil out of the dip stick on the first three pulls! The handle was hollow so the dyno tech just plugged it! What a mess! Come to find out the PCV valve was not closing causing the crankcase to see boost. Thought that might be the reason I was losing boost and losing power at higher RPMs because the engine was fighting boost on the crankcase side. Got it all back together and boost is still dropping off in the upper RPMs!! Is this turbo too small. Do I just need to put in a 12 PSI spring or slap on a MBC and turn it up on the dyno. The turbo is a 61mm Precision turbo with a .85 AR turbine housing and .60 compressor housing. Another problem I am having is it smokes bad when sitting at idle, oil for sure as I can smell it burning. No smoke when you drive it at all. The drain line has no dips and is a nice radius all the way to the pan and even the dyno tech said it looked good and shouldn't be the problem. When I took the intake pipe off last night after driving to check the boost again their was a puddle of oil in the pipe. When I finished the build I only ran the new motor for about an hour cause thought it was running to rich and didn't want to take a chance in washing the rings or cylinder walls. Trailered it to the dyno. I need Ideas!!

 

Sounds like the turbo is leaking oil. Might try putting a restrictor in the feed line.

As for boost falling off, it sounds like the turbo is just too small, or the housing it too small.

 

dude i got the same problem! I cant get my boost to stay up over 10 psi i can turn it up as high as i want but it always always always slowly creeps dback down to 10 during the dyno run. Im gonna check the exhaust pressure before the turbine. It should be less than 2:1 ratio from boost to exhaust pressure difference. So if i see like say 25 psi on the exhaust then its probably blowing the wastegate open and letting the boost fall. Maybe i just need a tougher spring in the wastegate i dont know yet test and tune!

 

I dont know about the boost loss, but my holley intake was puddling oil everywhere and smoking bad. I read a thread on here about a poor design on the pcv baffle on the lower intake allowing oil to get drawn into the upper. I plugged my pcv and added two vc breathers and have zero oil in the intake. Hope this helps

 

My favorite trick is completely disconnecting the wastegate reference line. If the boost still falls off the turbo is probably too small. Or maybe the exh pressure is pushing the poppet valve open.

 

add control pressure to the top of the gate via ams500 or ams-1000 .