View Full Version : SBC LOSSING RPM
I blowup my old 350 in my altered and put together a new 355 and tolk it to the drag strip after making some easy passes on it I ran it all out. I could only get 6500rpm out of it then the next pass was only 6300rpm and the next pass was only 6000 and every pass I made less and less RPM . I check valve spring pressure before putting springs on heads they had 745 psi and were rated for 747psi. I have checked and rechecked lash settings I ran a comp. check with 180 psi on all cylinders. timing is lock at 36* this cam is a 4/7 swap solid roller it is the first 4/7 swap cam I have ran I think it sounds different from the left to right bank. they were new sparkplugs and I put another new set in. I'm using the same distributor msd 6al 8000rpm chip and coil as was used with the old motor. at idle ech header pipe is about the same temp so all cylenders are firing at idle. Off idle or under load don't know.
sarry for the long post
oldandtired
08-04-2009, 01:02 PM
Monday at Pocono, Jimmy Johnson had a bad spark plug. You might start there.
Dave
fla1976
08-04-2009, 01:11 PM
I would check the fuel filter.
Are the butterflys opening completely?
cepx111
08-04-2009, 09:09 PM
Check to make sure your getting WOT.
The boy's mustang was doing the same thing, found out it was only getting half throttle :shock:
Just a thought>Cp
mytmouz
08-04-2009, 09:17 PM
Sounds like the valve springs are going away...
chevyfireball
08-05-2009, 04:21 AM
Sounds to me like the throttle linkage is shaking loose. Check the lock nut. Ya did remember to attach the plugs leads in a different order on the old dizzy eh?
The first thing I checked was the throttle cable and am getting WOT. The sparkplugs I tried 2 new sets. I just thought of it do you think it could be the 8000 RPM msd chip is breaking down.
curtisreed
08-05-2009, 10:26 AM
Have you checked for any metal in the oil filter? My experience is usually chips are good or completely bad no in between, but it is an easy part check. Have you verified your timing hasn't moved? As was stated before fuel flow, I.E. filter, flow from pump, etc. Brakes dragging, rearend gear problem. Convertor could be going bad, have seen this before, we chased a fuel problem for a while until the convertor showed us enough to figure it out. :oops: :oops:
Curtis
ashbros
08-06-2009, 09:40 PM
Hows the oil pressure and fuel pressure.
Check the fuel filters, plugs, plug wires, throttle linkage.
Is your hold down/locking bolt tight or has it came loose.
Check your fuel for water.
Check the cog on your distributor. Are the grears ground down?
Let us know what you find out..
have not been into town to look at car will this weekend. will let you know what I find out.
thanks
I got it fixed ended up being the mallory unilte dis. as the rpms went up it would pull out timing.