I have only 700 miles on my 383 sbc and was able to spin the hell out of my street tires with only have to 3/4 throttle. Now I have to go WOT to spin the tires and my hp is very low. I put it in the shop to Dyno tune and they tell me that my rear torque is only like rwtq318 and rwhp is like 302. I don't know what happened. One day I took the car out and ran fine, next day I have no more power off the line and it breaks up at around 6000 rpm. Did compression test and all cylinders are within 180-190 psi. Changed spark plugs, wires and a new race distributor and still no difference.

Any clues would be very appreciated.

 

You might have some flat cam lobes. Is it a flat-tappet cam?

 

no valvetrain chattering or anything out of the ordinary?

 

How can I tell if I have flat lobes? And yes, it is a flat tappet cam and I've always heard noise from the roller rockers.

 

Is it possible that you over reved it, and floated the valves? It only takes one time to hurt the springs.

 

I have never revved it past 6500 rpm and it should spin safely to 6800-7200 with the cam, heads and bottom end. And is there anyway to test the valves or springs for over revving?

 

7200? What kind of valvetrain are you running? The combination may make power up to that point, however, if the springs were not properly chosen, and installed for the cam you are running, (seat pressure,etc),you can very easily over rev the engine and float the valves. If the spring can no longer control the valve at a paticular RPM, then float will occur. The heat that is generated in the springs, will ruin them. Same as cutting a coil spring with a torch. That is alot of RPM for a flat tappet, IMO.

 

[B]

Oh, BTW, You would have to remove them, and check the spring pressures. If they are messed up, some will stand taller than others if you look at them while they are standing next to each other. If it did indeed float, hopefully, only the springs are hurt.

 

They are the standard beehive single springs that come with the WP Sportsman II heads, rated up to .550 lift.

 

Also, wouldn't the Dyno show if I was having valve float?

 

It would show the engine is down on power. If they are good to .550 lift, well thats OK. What causes valve float is weak, or worn springs, heavy valvetrain parts, (lifters, retainers, etc), and excessive RPM. A spring can not be expected to last if its going to be reved beyond its normal range. BTW, are your springs the stock diameter, (1.250), or larger?

If you cant find anything else wrong, set an afternoon aside and pull the springs.

 

Stock diameter 1.250.

 

Would any of this explain why I have no more power off the line? I understand springs maybe the problem at top end, but why no low end?

 

ttt

 

Anybody???

 

What is the update? Have you done any troubleshooting? Vacuum test? Compression and/or leakdown test? Have you pulled the valve covers and inspected the lash to see if the lobes went flat? Keep us posted.

 

Compression test and all cylinders are within 180-190 psi. Changed spark plugs, wires and a new race distributor and still no difference.

No gas in the motor oil. Carb has been dynoed and fuel pressure is 8 psi at WOT. 0 Valve lash for Hyd. Flat Tappet.
Cut the oil filter and found no metal shavings or chunks.

Vacuum has always been low around 10-12 psi with that cam.

I guess the next thing is to remove the intake and measure lobe lift from the lifters.

I'm thinking either bad lifters valve springs, torque converter or maybe it is the cam.

 

If your getting 8-10psi vacuume you have a serious problem

 

Sorry, I corrected that to 10-12 psi.

 

If the lash is still 0 the cam is probably good. I have wiped out flat tappets. They go real flat when the go. No metal in the filter is a good sign.

 

I agree with this. You can measure the same lift numbers at the top of the pushrod without pulling the intake. After I broke-in my 350 I noticed the idle get "better", which for a 108' LSA cam is not a good sign. The cam (hyd) was new with the dull finish on the lobes. I had lashed it "just snug" and after break-in it it had picked up a good .010 lash which will drop a good 15' off of the duration and overlap. I tigtened the lash out and my "bad" idle was back along with the upper end power. I think your problem is intake gasket related though or something changed in the carb (causing lean). Valve springs going soft won't affect power below 4000.
BTW WHERE did you get the 4.10 gears for your 9-bolt!!???

 

Any way to test the theory of an intake gasket issue? Don't think it was anything changed in the carb, when the shop dynoed the carb, wouldn't they have caught that something was wrong with it?

Also, the gears are from www.9bolt.com. Miles is his name.

 

You dyno'd the carb after the power loss? I read it as it had been dyno'd when you got it. 9BOLT.COM shows:
"The following 9 bolt parts are currently available (some in very
limited quantities) as of 12-29-04" Talk about up to date.
I guess it's right about having to "call" them. Wish they would get "net-ready" so I can see what new parts prices are. Only new set he shows a price on is the 3.73. I like ordering online. I work 11-12 hours per weekday and can't get diddley done during "working hours".

 

If the cam went flat, is there usually metal in the oil filter? And would the lifters have a sign on it at the bottom of the lifter?

These are question that I ask to decide if I should remove the intake or not.

 

1 flat lifter lobe makes a ton of metal. None in the filter is a great sign. 1 ripped down a fresh 305 with a flat lobe. I about puked. So much damage it was sickning. I havea hunch yours is ok.

 

I did pull the oil filter and cut it open and found this gray wet-powdery substance. Not sure if that was the pre-lube or what. And the oil pan drain plug is magnetic and I found these little metal shavings on the tip of the magnet. And I did replace the valve springs just over the weekend and still down on power.