[66 Buick Special]

I have been having issues with my new motor not pulling well beyond 5000 rpm. It hit 5000 and just hangs there. Then after a couple of seconds it will slowly wind up to 6000 where I shut it down.

Today I put it on the dyno and could only get partial info. The operator said that the torque numbers were registering intermittantly, possibly due to my not having a ground strap.

Here's what I got, I know it's not much. Notice how the first 2 runs on motor and the 3rd run where I hit it with a 125 shot on a cold 700lbs of bottle pressure look almost identical in the shape of the graph. The A/F was in the low 12's throughout the testing. Fuel was about 98 octane (pump 92+2oz kemco per gallon).



This is a SBC 350+.030
10.76:1 static comp,
4340 forged rotating assembly, fully balanced
GM Bowtie Phase II 2.02/1.60 184cc heads
Valve springs are Crane duals (sorry I don't remember the poundage specs)
Voodoo 60104 233/241 @ .050 - 276/284 advertised, 504/525lift 110LS
Crane Energizer roller rockers
RPM Air Gap
Holley 4779 750 double pumper jetted 72/84
1 5/8" mid length headers with 3" collectors
2.5 duals

2700 10" stall flashes at 3500
12 bolt w/3.90 posi

I'm running a Holley 130gph mechanical pump 6.5lbs of fuel pressure
Stock 5/16 pickup and line to the pump.
I am going to replace the sending unit and line with 1/2" versions very soon.
I have been thinking that the 5/16 line was holding me back but the A/F stayed consistant, never going lean...

Any idea's why it is holding at 5000 and struggling to 6000?

 

[stock48]

I don't know much about N2o but you could be getting into valve float. I don't know what AFR N2o likes but I try to stay around 11.2~ 11.5:1 with my turbo's. A week ignition, and or plug gap too wide can also act that way, but like valve float you should go rich. What's your exhaust system like? 2.5'' pipe should be large enough, but if you have some $hitty mufflers, or tail pipes that could choke your top end too.

 

[66 Buick Special]

I have 2.5 duals with short Magnaflows exiting under the bumper.

Ignition is an HEI with Accel coil/cap/rotor/wires/short header plugs at .045.
I am running a stock module though.

The flattening at 5000rpm was the same on motor as it was on nitrous.
Mixture stayed the same on and off the bottle too.

 

[rustbucket79]

I would look at upgrading the module, been there had trouble with that.

Otherwise, your chart looks painfully similar to the other thread here, "bad day at the dyno", and hey, you're running a Voodoo cam as well, HMMMM.

Find out what you have for seat and open pressure please.

 

[usnavyame70]

the chart looks something like mine except you put down more power and more torque with a smaller cam.something isnt right with either of our motors lunati will be getting a call tomorrow from me.if i find something out i will let you know

 

[66 Buick Special]

Matt, definitely let me know what you find out. I know this motor has more in it than this.

Rustbucket, I saw Matt's dyno thread and almost chimed in there, but I didn't want to confuse matters. Thanks for the suggestion on the module, that would be a fairly cheap and easy thing to try. I've got a call in to my friend that set the heads up to see if I can get the installed numbers on the springs.

I'll post them when I get them.

Thanks!

 

[Tom Mobley]

let's see, nice 355 with Harold cam, 5/16" fuel line, hangs at 5K. What's wrong with this picture? I wouldn't spend any money or time on other stuff til you get this glaring 5/16 deal fixed.

I think you're lucky you still have 8 pistons. Got any tiny black specks on the spark plug porcelains? Didn't that dyno guy have a wideband O2 setup? You can get one for $300, cheaper than a carb or some high zoot ignition deal. After you get your stuff straightened out you can sell it for $250 easy.

 

[curley8788]

change out that fuel line, regardless of what that a/f says. 5/16 is no good. im going through the same BS with my car. the dyno operator stopped after one 4000 rpm pull.

and like itold matt before, throw the same springs on that i have in my motor with a voodoo 60104. they are the 74818LUN beehives. 168 bucks on ebay with free shipping.

 

[rustbucket79]

Quote from the initial post: I'm running a Holley 130gph mechanical pump 6.5lbs of fuel pressure
Stock 5/16 pickup and line to the pump.
I am going to replace the sending unit and line with 1/2" versions very soon.
I have been thinking that the 5/16 line was holding me back but the A/F stayed consistant, never going lean...

Any idea's why it is holding at 5000 and struggling to 6000?

He had the A/F with positive results. I agree that he's living on borrowed time with the small supply line, but the A/F doesn't lie. How long did this test take? Other than the nitrous run, I don't know how much the fuel system even matters on a short full throttle blast on a chassis dyno. Doing the same nitrous run on the quarter mile could potentially have him scraping piston chunks off his spark plugs.

The fact that the 3 curves look suprizingly similar holds the clue IMHO. If it was an ignition issue it should have showed up earlier in the RPM due to increased cylinder pressure which increases ignition demand. Regardless, a better module is a wise investment, once he gets the engine running properly it will need a more reliable ignition. (spins it to 6000+)

The fact that his and the other "dyno woes" thread are pretty much a zerox of each other in terms of shape and power fluctutation at roughly 5000 lead me to believe they have similar valvetrain control issues. An interesting (and time consuming) test would have been to shim the springs up .060" or so and made another pull. It could be harmonic related, but likely lifter and/or spring pressure related.

 

[66 Buick Special]

Find out what you have for seat and open pressure please.

My springs are Crane 99893 set at 1.875 @ 120.

Crane says.. 1.460'' diameter double spring. Valve lift up to .690''. 120# @ 1.875'' closed, 426# @ 1.110'' open, coil bind @ 1.080''.

We are going to try shimming them .060 and see if that changes anything.
My friend that assembled the heads was in attendance at the dyno pull and he mentioned we might try shimming them .060.

When I posted looking for help on here, Doug "rustbucket" said that it would be interesting to see what would have happened if we had done that as well.

All it will cost is time to try it. If it doesn't work or at least move the problem up the rpm scale then I think I can look at other stuff.

I'm still going to buy one of mcrobb's new 1/2" sender/pickup units and I have the 1/2" tubing already.

Then I'll throw that modulator at it if it still won't run.

If all that doesn't work I'll step back and scratch my head some more.

 

[FourEightyNine]

you could just run highway gears

haha sorry just trying to lighten up the atmosphere

I still think its fuel.

 

[66 Buick Special]

You could be right Brian. I'm definitely not counting it out.
I know it worked for you.:yes:

 

[usnavyame70]

Hey greg i was just wondering what dyno place you where using.and also who are you using to help you shim or maybe change your valve springs since i am haveing trouble finding someone to help me

 

[rustbucket79]

My springs are Crane 99893 set at 1.875 @ 120.



We are going to try shimming them .060 and see if that changes anything.
My friend that assembled the heads was in attendance at the dyno pull and he mentioned we might try shimming them .060.

When I posted looking for help on here, Doug "rustbucket" said that it would be interesting to see what would have happened if we had done that as well.

All it will cost is time to try it. If it doesn't work or at least move the problem up the rpm scale then I think I can look at other stuff.

I'm still going to buy one of mcrobb's new 1/2" sender/pickup units and I have the 1/2" tubing already.

Then I'll throw that modulator at it if it still won't run.

If all that doesn't work I'll step back and scratch my head some more.

ASSUMING......You have the pushrods/rockers/valvetrain etc. that are capable of the added spring pressure, I would consider even .090" less installed height.

WAIT! Brain was thinking you have a hyd roller, you have a flat tappet. Installing those springs at 1.815 (.060" shimmed) will put you at 143# seated, 348 open using Crane's specs. That's a little stout for a hyd flat tappet cam. I'm not saying it wouldn't work, but I would be calling Lunati before attempting these pressures. Of course, what the book lists for pressures and reality rarely match, but I would be tempted to try 135/325 which should be a .030" shim. (again, relying on everying being as per specification currently) This is where you need to take your time and measure all your installed heights and measure your current and open pressures.

 

[66 Buick Special]

Hey greg i was just wondering what dyno place you where using.and also who are you using to help you shim or maybe change your valve springs since i am haveing trouble finding someone to help me

Darryl "Fryntyr" on here is helping me with the springs. He's heading out of town for a couple of weeks so there is going to be a slight delay in our experiment. If you just need a spring compressor post it in the NW section and see if someone else local might have one for you sooner.:yes:

The dyno outfit is DKDiesel Performance & Offroad. They brought out a portable Dynojet for the TCNW get-together we had in Arlington at Hoss's house (Red Rocket Racing on this site). Here's the link to the thread with pics and my winning "I'm on fire" smokey burnout and some pics of the dyno.
http://www.chevelles.com/forums/showthread.php?t=228799

Doug, thanks for looking out for those spring pressures. We will definitely take that info into consideration.:yes:

I'll definitely share what we find out.

 

[rustbucket79]

Glad to help Greg, I want to see your problem fixed, but not at the cost of a wiped cam in 10,000 miles.

Good luck!

 

[66 Buick Special]

Instead of opening a new thread I thought I would tack this on here since it gives background to my situation.

I developed a significant header gasket leak at the #1 cylinder flange during my award winning burnout. I have to wait until Friday to pick up new header and collector gaskets but tonight I pulled the headers to get them ready.

This meant I had to pull my plugs to get the headers out. I noticed as I was pulling the plugs out, that 7 off them looked virtually identical, but the #3 plug looks different. I thought I'd post a picture and see what you guys come up with.

Now this is NOT a "make a pass", shut her down, read the plugs scenerio... The car was driven mildly about 40 miles (mostly highway 3200rpm) on the way home from the dyno /burnout event so I know this isn't the optimum situation.
Any thoughts? #3 is on the left, #1 is on the right and representitive of the rest of the plugs.

 

[rustbucket79]

Are you noticing a coolant loss in the rad?

 

[Kevin R]

Greg thats what my plug in my cracked head looked like.:sad: I hope thats not the case bud.

 

[66 Buick Special]

I have lost a little coolant but there was some in my catch can so I didn't think anything of it. The motor usually runs about 160-170 with a 180 thermostat. It has only gotten to 210 once and that was during the previously mentioned burnout.

Sounds like a compression test is in order. Do you think it would be worth running through the torque sequence on that head ? I'm running a standard .039 Felpro blue gasket.

I haven't seen any milky oil but I know that doesn't mean anything.