I'm going to try and keep this short as possible but we have a very weird issues going on,67 valiant,727 trany,ladder bar suspension,New msd distr.360 motor--our first time out in Martin mich car ran 10.4,10.5,10.6,10.4 and was going thru the traps at 7600,last run zach said something happened at the far side of the track that run he was 11.6 so a full sec was lost and only went thru the traps at 7,000 so car came back to Wis and went to test and tune the next tues car ran 11.6,11.7,11.8.11.5 going thru the traps at 7,000,so we still lost 600 rpm,last night we went and it was the same at 11.6,11.7,11.5 and only going thru the traps at 6700 so in total every time out were losing rpm's??? a total of 900 rpm's has been lost and now we are lost???????? car launches like a mother 60 ft times around the 1.5 consistent time,Where does a car drop a sec and 900 rpm??????? Converter???????? Thanks Steve
Race car mystery-Help us solve PLEASE
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longarm
Car sold back to original owners
Valve springs
mikedevore
Well-Known Member
I just fought a simular problem.
My Barracuda went from 6.40 @ 106 MPH to a 6.90 @ 99 MPH.
Thought it was the convertor, sent it in, tighten it up.
Same numbers. sent the convertor back, loosened it up.
Same numbers.
The problem was when the heads were ported, the porter had broken thru the casting on a intake runner at the push rod pinch. It had been brazed up & blended.
ran a leak down, worst cylinder was 2.5 percent.
removed the rockers & installed a plate to vacuum check the intake & heads.
I was suspecting a failed intake gasket.
I could blow into the hose that was hooked up & see it leaking out when I sprayed wd40 on it.
I have since put epoxy on it & going to run it this weekend to see if that fixed the problem.
That lost numbers seem like alot for valve springs.
Check the basics, leakdown to eleminate the short block.
I also had a friend with a 340 that no matter what you did, it would only run 11.20's every time.
I installed my carb (750 holley) same as his & changed the dist., same as his.
The car responded with a 11.56 pass.
These kind of problems will eat you up.
My Barracuda went from 6.40 @ 106 MPH to a 6.90 @ 99 MPH.
Thought it was the convertor, sent it in, tighten it up.
Same numbers. sent the convertor back, loosened it up.
Same numbers.
The problem was when the heads were ported, the porter had broken thru the casting on a intake runner at the push rod pinch. It had been brazed up & blended.
ran a leak down, worst cylinder was 2.5 percent.
removed the rockers & installed a plate to vacuum check the intake & heads.
I was suspecting a failed intake gasket.
I could blow into the hose that was hooked up & see it leaking out when I sprayed wd40 on it.
I have since put epoxy on it & going to run it this weekend to see if that fixed the problem.
That lost numbers seem like alot for valve springs.
Check the basics, leakdown to eleminate the short block.
I also had a friend with a 340 that no matter what you did, it would only run 11.20's every time.
I installed my carb (750 holley) same as his & changed the dist., same as his.
The car responded with a 11.56 pass.
These kind of problems will eat you up.
we also replace the intake gasket and have since tested it with the ol carb cleaner test and no rpm increase,I agree on the valve spring, losing 1.2 to 1.5 sec is a big loss,we also changed carbs and it ran the same-we have a/f meter also and cars runs 12.0 to 12.5 at W.O.T. --Steve
just talked with lenny at ultimate converter cause it's his converter in the car,He said most likely not the converter because when a converter goes it reacts the opposite,it rev the engine higher or slip like a bad clutch in a 4 speed--Steve
moparlover
Well-Known Member
does the engine sound the same?
"last run zach said something happened at the far side of the track that run"
could be something silly like a plug wire grounding out, or bad ign box, rev limiter, fuel starvation (fuel pump has a short) etc.
i'm guessing electrical, second choice would be cam timing / chain
third guess would be one cam lobe / rocker or pushrod.
you could put fresh plugs in, take a few passes and compare all 8 that might help
"last run zach said something happened at the far side of the track that run"
could be something silly like a plug wire grounding out, or bad ign box, rev limiter, fuel starvation (fuel pump has a short) etc.
i'm guessing electrical, second choice would be cam timing / chain
third guess would be one cam lobe / rocker or pushrod.
you could put fresh plugs in, take a few passes and compare all 8 that might help
might want to look at some of the little things ...like did the distributor move?....did you check the throttle cable to make sure it did not slip and not getting full throttle...
i would pull the valve cover and look and check rockers....also compression test ....need to verify that the engine is mechannically sound.
i would pull the valve cover and look and check rockers....also compression test ....need to verify that the engine is mechannically sound.
New dist.New wires,new plugs,throttle cable checked for full opening of throttle plates,Brand new 7Al-2 ign box,New complete wiring and grounding in car,Checked timing 13 initial and 34 total,We are going to see if the cars like more timing but till we get the rpm's back don't think i would adjust the timing yet,Brand new complete fuel system,-10 lines and holley black pump,fuel pressure stays strong down the track at 7.5 to 8 psi,float levels checked in the carb.
Moparlaover--Had a friend along last night at test and tune who's been racing for 40 years in pro stock,He listened and watched the car at the launch and at the end of the track to see if he could hear the car break up at all during the run,to him there was no obvious carb or ignition break up in fact he said a couple times,"that dam car sounds strong" and didn't hear anything out of the ordinary.
You might check or replace your coil, that might be the culprit.
pettybludart
Well-Known Member
How old is the foam in your fuel cell?Maybe breaking down,getting caught in pump/filters?This happened to a friend of mine..had to change the foam and clean the whole fuel system.It was shocking to see how much foam bits were in the system.
moparlover
Well-Known Member
hmmmm no ticks or misses.
double and triple check this >>>
sometimes new parts work good then slip out of adjustment when they break in. maybe one of the lil springs jumped or streched or somethin weird inside. i dont think it would make it miss but maybe just lose a little oompa
also is it electric water pump or belt driven? could be draggin if it's belt drivin. same with alt. you might have to pull the belt make sure stuff isnt binding. also a weak coil. but you cant really test them without a swap. dont try the manual test method lol
double and triple check this >>>
sometimes new parts work good then slip out of adjustment when they break in. maybe one of the lil springs jumped or streched or somethin weird inside. i dont think it would make it miss but maybe just lose a little oompa
also is it electric water pump or belt driven? could be draggin if it's belt drivin. same with alt. you might have to pull the belt make sure stuff isnt binding. also a weak coil. but you cant really test them without a swap. dont try the manual test method lol
My car did the same thing halfway through last season and into this season. I found #5 intake lobe had gone flat. Car seemed to run ok, just slow. Had a loud ticking noise when I pulled into the garage last weekend. Pulled a valve cover and found the bad lobe.
My vote would be valves spring gone weak.
here is a couple other thoughts. bad axle bearing or maybe in the ring and pinion area.
A rear drum brake adj up to much.
has the car become harder to push lately?
When you look at your ET slip, were does the ET start to fall behind?
here is a couple other thoughts. bad axle bearing or maybe in the ring and pinion area.
A rear drum brake adj up to much.
has the car become harder to push lately?
When you look at your ET slip, were does the ET start to fall behind?
FIRST OF ALL THANKS TO ALL OF YOU !!!!!!!! I'll try and answer some more questions:Brand new fuel cell and we pulled filters and they were spotless,intake was off after Martin and inspected the cam and lobes, Cudafever GOOD CALL we will pull wheels and drums to inspect tomorrow night before test & Tune,Also will try a different coil--Steve
Cheapstreetduster
been here a long time
sure.... that rocker will also have a huge amount of lash in it...
a compression check will tell you if you have a bad valve spring or bad lobe.
it will jump right out at you as way off the number...
look at all the psi numbers...and the one thats off will tell you which cylinder ..be the culprit.
moparlover
Well-Known Member
well after you get done with the other checks...
maybe you can take off the fuel pump and check the timing chain, if you have some kind of way to scope it.
you will probably have to wait until after the season for this one... to see if the cam is still degreed the way it was when new.
do you still have records of the cam degree settings from when you built the engine?
If you have a line lock, make sure the valve isn't sticking shut (holding pressure...although that would probably be obvious), check the rest of the braking system as well. Comparing time slips from some good runs to the runs in question would help diagnose the problem...that way you could see at what point in the run it is falling off.
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