71 Duster 360 turbo build

[turbovan]

What are the symptoms of valve float? Does it happen under any amount of boost or only when you get up into the higher PSIs? Is this with the exhaust wide open? I noticed in my back pressure tests that my RPM was hitting a 5800-5900 ceiling when running through the muffler.

Under boost on a pull it will rev to 6000, but not beyond no matter the boost level. It does make a breaking up noise, but not popping. AFR appears about normal and timing looks good. I closed the plug gap from 30 to 22 with no change.



Driving the car slowly increasing rpm(no boost) causes it to break up at 5800. It almost sounds like the valves are hitting the pistons for that fraction of a second, but I’ve noticed no repercussions; compression check still good.

Spring pressures before install were 130 on the seat and around 330 open(.600). Advertised as 145 and 360 open(no height given).


White is rpm. 6k flatline

 

[turbovan]

 

[turbovan]

Oregon camshaft did not have a valve spring recommendation for me. He just said he wouldn’t run more than I already have. Another shop I spoke with stated they typically run 170-420 with magnum lifters. I’m running Elgin HL-2269s lifters where are supposed to be a slow leak down type. I have 2.5 turns of preload on them which I’ve seen recommended for factory lifters. It was suggested that I try 1/4 turn preload since they’re slow leak down. Maybe I’m experience pump up?

 

[Landy Duster]

Something does not seem right there. My iron headed 318 Magnum (stock cracked heads) with a Comp 20-746-9 HR cam (.506" lift), Magnum Swap valve springs, HD MP lifters and stock rockers will pull well past 7K under 20 psi of boost on E85 (and 18°of timing). I have an MSD Programmable box and a HVIC coil going thru an MP distributor, 8MM wires to NGK -7 plugs gapped at .045". I finally experienced blowing out the spark at 26 psi. My engine NA will not rev over 6K. I think it may be lifter pump up.

 

[subcom]

Is this Megasquirt? It’s not the rev limiter or AFR safety system kicking in at 6k?

 

[turbovan]

Microsquirt. Rev limiter set at 6500rpm, and I do not believe I even have any AFR safety’s available.

 

[turbovan]

Something does not seem right there. My iron headed 318 Magnum (stock cracked heads) with a Comp 20-746-9 HR cam (.506" lift), Magnum Swap valve springs, HD MP lifters and stock rockers will pull well past 7K under 20 psi of boost on E85 (and 18°of timing). I have an MSD Programmable box and a HVIC coil going thru an MP distributor, 8MM wires to NGK -7 plugs gapped at .045". I finally experienced blowing out the spark at 26 psi. My engine NA will not rev over 6K. I think it may be lifter pump up.

Mopar HD hydraulic roller lifters? How much preload?

The lifters I’m running are the stiffest I’ve ever dealt with. Before I adjust the rockers I have to slowly turn the engine over and let it sit at high lift spots so that the lifter will bleed down over a couple minutes.

 

[Landy Duster]

Yes sir, Mopar Magnum HD roller lifters, I bought the last set in the US, slightly bigger shaft harder roller. Whatever preload the have with the thinner Cometic head gaskets and stock pushrods & rockers. Probably around .100". They creak when they bleed down and it takes a few minutes before they stop making noise. I would refurb a set of stock lifters (disassemble, inspect, clean, and reassemble) and use them.

 

[turbovan]

What are your valve spring pressures? What’s the cam look like? I have confidence in my lifters. At least more in them than my valve springs at the moment. I’ve never had a small block that could turn more than 6k rpm so there is a significant possibility I’m doing something very wrong.

 

[Landy Duster]

I have no clue what the spring pressures are, but I do plan on putting new springs and retainers on. These springs have about 100 passes on them and have been over 7k about 10 times, but usually gets shifted at 6600-6700. The cam looks fine. NA I don't think this cam would turn much over 6k.