71 Duster 360 turbo build

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subcom said:
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.
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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
IMG_2291.jpeg
 
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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?
 
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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.
 
Is this Megasquirt? It’s not the rev limiter or AFR safety system kicking in at 6k?
 
Microsquirt. Rev limiter set at 6500rpm, and I do not believe I even have any AFR safety’s available.
 
Landy Duster said:
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.
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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.
 
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.
 
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.
 
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.
 
Half way through valve spring replacement, and I have to say I’m glad I’m going through the valvetrain. The Speedmaster valve locks are in rough condition. Possibly because I was floating valves, but the majority I’ve removed are chewed up. The intake springs were all shimmed with 4 x .020 shims; 2 x .020 shims on the exhaust. Retainers and valves look fine. I’ll be sending the heads out for new valves this summer, and hope everything holds together for a couple races before then.

I’m also hoping to replace the lifter retainer wire clips with internal snap rings while I have it apart. If I can find them in time.
 
Engine is all back together and sitting for the summer until the heat dies off a bit. After months of debating I decided to order or build a Dana 60. The 8 3/4 might have handled the power just fine, but it’s the last “weak” link in my drivetrain so it’s going up for sale. I’m also looking to buy some ID1000 injectors to ensure my pistons stay the same shape. The uncapped ford injectors are definitely flowing well (scaled at 960), but guessing they all flow the same is a poor decision. This thing will make it to the drag strip…eventually.
 
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turbovan said:
Microsquirt. Rev limiter set at 6500rpm, and I do not believe I even have any AFR safety’s available.
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are you sure your tach or what ever you are using it to read rpm is not off 500 rpm. I mean you could be hitting your 6500 rev limiter but its showing you are only revving it to 6000. have you tried setting the revlimter to 7000 and see what it revs to? I could be way off base here. but its just a thought.
 
turbovan said:
Engine is all back together and sitting for the summer until the heat dies off a bit. After months of debating I decided to order or build a Dana 60. The 8 3/4 might have handled the power just fine, but it’s the last “weak” link in my drivetrain so it’s going up for sale. I’m also looking to buy some ID1000 injectors to ensure my pistons stay the same shape. The uncapped ford injectors are definitely flowing well (scaled at 960), but guessing they all flow the same is a poor decision. This thing will make it to the drag strip…eventually.
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Have you considered a Ford 9”? That would be my choice if I was to replace my setup.
 
subcom said:
Have you considered a Ford 9”? That would be my choice if I was to replace my setup.
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I did in fact end up ordering a 9” from speedway. Parts started arriving today! I also came upon your thread regarding axle centerline to yoke difference for the 8 3/4 and ford 9”. I’ll throw an update in there for future users once I measure them side by side. I see 1” longer yokes available for the 9” so I’m hopeful that will be just enough to retain my Strange driveshaft.
 
turbovan said:
I did in fact end up ordering a 9” from speedway. Parts started arriving today! I also came upon your thread regarding axle centerline to yoke difference for the 8 3/4 and ford 9”. I’ll throw an update in there for future users once I measure them side by side. I see 1” longer yokes available for the 9” so I’m hopeful that will be just enough to retain my Strange driveshaft.
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Nice! I remember considering the Speedway 9” also. They had a good selection and price. Good call!
 
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