Ive figured out my speedo is off around 15 mph judging by the radar machines around town before I put headers on I couldnt hit more than 90-95 on my speedo then it would start acting like it was floating a valve. spitting and sputtering and back firing. well I went ahead and added headers and got my exhaust welded back up and now tonight I ran it all out to see what difference the headers made and I manged to runt the car right on up to 110 and then it was all done all through it wouldnt pass 110 I even let off a little and got back into it to try and sneak up on it but nope it wouldnt do it. I dont get it why wont it wont go any faster my other comet easily hit 135 on the dyno and 140 on the highway and that speedo was really close to right on. and my sons old comet had a BONE STOCK 302 that ran 130 ish and that speedo was about 5 mph off according to the radar machines around town a little info about the car I dont know what has been done if anything inside other than the comp cam it has a 512 lift and 268 duration posi 8 inch rear end with 3.55 gears headman headers and dual 2 1/2" exhaust an hei distributor I figure I should easily be able to to crack 100 any ideas why it wont run over 100mph?
I am having the same issue but I can't get the mav to go over 80 in fifth. I am thinking it has to due with timing but I am lost as well.
Could be insufficient fuel supply or low fuel pressure. When I disassembled my car for restoration, I discovered a previous owner had jacked the car up at some point and crushed the fuel line.
I have a new metal fuel line although it is bent around the back of the motor so it doesnt have to go up and over the top of the motor. I havent checked the throttle position but I havent touched the carb since removing it from my other comet that went 140 same intake manifold as well (I blew the motor in my other comet so I scavenged as many parts as I could for this motor)
Can you install a fuel pressure gauge and find out what pressure you have at idle vs what it should put out at both idle and at WOT then mash on it and if it calls for 7 psi then drops to 2 psi, well there it is.......this is a SWAG on my part just thought I'd throw it out there
How do you figure it was going 140 when the speedo doesn't read past 120? I've had mine past 120 and the needle was bouncing. It's 5mph off so I wasn't going faster than 120.
the way I figured 140 was the needle was WAY past 120 it was beyond bouncing. I figure the cable was close to breaking. the computer at the dyno shop read 135 before we let off so I know it was more than capable and I would think this motor would be able to as well since it has the same cam intake carb and distributor
what carburetor are you using? what fuel pump are you using? what sizes are the fuel lines? do you know anything about the valve springs? were they replaced with the cam? what transmission do you have? whats the rear gear ratio? whats the rear tire height?
carb us 600 edelbrock stock pump (same as other cars) dont remember the line size we went and bought the same as we had on my other comet since it worked so well the valve springs werent replaced as the shop said I didnt have to I have a c4 with 2500 stall stage 3 shift kit rear end gear ratio is 3.55 tires are 205-60-15 wheels and tires snagged from my other comet when it got put on the back burner until the new motor is done
the must probable suspect would the the secondaries of the edelbrock carb are not fully opening. the main throttle plates may be opening all the way but the vacuum flap above the venturis may not be opening fully. what rpm does it seem to maxing out at that speed?
