Worn cam?
Thread Starter
2nd Gear Member
Joined: Jul 2007
Posts: 322
From:
Worn cam?
Hi,
My mechanic suspects that the stock cam in my engine is worn. I believed it was replaced when the engine was rebuilt about a year ago, I am not completely sure though.
What could be the symptoms in this case? I have some good power on the mid-high range and moderate power on the low range. My throttle response is just ok (i.e. not very impressive) and when I really hammer it down, it is not very smooth until I get to 3k+ RPM.
Thanks,
My mechanic suspects that the stock cam in my engine is worn. I believed it was replaced when the engine was rebuilt about a year ago, I am not completely sure though.
What could be the symptoms in this case? I have some good power on the mid-high range and moderate power on the low range. My throttle response is just ok (i.e. not very impressive) and when I really hammer it down, it is not very smooth until I get to 3k+ RPM.
Thanks,
6th Gear Member
Joined: Aug 2007
Posts: 5,896
From: Elk Grove, CA
Sounds more like a timing issue. A chopped cam lobe will result in oddball compression readings from that cylinder (air can't flow in or out of the chamber fast enough). It will create a very loud, very distinct tapping sound which only gets worse as you drive. It may also create backfiring through the carburetor.
3rd Gear Member
Joined: Apr 2007
Posts: 882
From:
Sounds like your mac needs to pay his rent because your cars symptoms have nothing to do with a warn cam. +1 on the timing
When was the last time you changed your plugs and wires and cleaned your dizzy cap?
Like StarFury said, If it was your cam, you would hear a loud tapping at high RPMS
When was the last time you changed your plugs and wires and cleaned your dizzy cap?
Like StarFury said, If it was your cam, you would hear a loud tapping at high RPMS
Thread Starter
2nd Gear Member
Joined: Jul 2007
Posts: 322
From:
Ok, I was not explicit enough, he suspects that because he saw that the valves on the passenger side were not opening completely (i.e. the thing with the springs were not going completely up, according to him).
I was just wondering if this would explain the fact that it is not very smooth and the bad throttle response. It may just be a little bit too worn?
I was just wondering if this would explain the fact that it is not very smooth and the bad throttle response. It may just be a little bit too worn?
4th Gear Member
Joined: Sep 2008
Posts: 1,839
From: Connecticut
A reliable machine shop would have mic'ed the lobes and journals of the old cam if they were going to reinstall it to ensure you had a proper part in your newly rebuilt engine. I'm still puzzled by the decision to reuse the original cam in a rebuild that you planned on adding upgrade parts to in the future.
Anyway, you can still check the lobes with a dial indicator while rotating the engine by hand.
Anyway, you can still check the lobes with a dial indicator while rotating the engine by hand.
Thread Starter
2nd Gear Member
Joined: Jul 2007
Posts: 322
From:
Thanks for your feedback.
Regarding the shop and what they did when they rebuilt it, I will try to find out today. What disappoints me a little bit is that I had to change the spark plugs myself when I got it back with the new heads because it was really running bad.
When you say that my stock cam is "starving the engine", what would be the noticeable symptoms? I believe that my top-end power is ok. Just to give you a rough idea, I was able to do 0-40 in 4.6 sec when my friend with a 300hp BMW 335ci did it in 4.9 sec. We did that with my dyno and did not have enough room to go to 60
To be honest, it was funnier to drive it before the new heads as it would not hesitate when I hammer it and it would start pushing even before 2k RPM.
Thanks!
Regarding the shop and what they did when they rebuilt it, I will try to find out today. What disappoints me a little bit is that I had to change the spark plugs myself when I got it back with the new heads because it was really running bad.
When you say that my stock cam is "starving the engine", what would be the noticeable symptoms? I believe that my top-end power is ok. Just to give you a rough idea, I was able to do 0-40 in 4.6 sec when my friend with a 300hp BMW 335ci did it in 4.9 sec. We did that with my dyno and did not have enough room to go to 60
To be honest, it was funnier to drive it before the new heads as it would not hesitate when I hammer it and it would start pushing even before 2k RPM.
Thanks!
5th Gear Member
Joined: Apr 2007
Posts: 2,100
From: Texas Hill Country
Having a stock cam with performance heads is like:
Having your mouth wide open and taking very short breaths. You are not starving your engine as much as not using it to its potential. A worn stock stock, if in fact that is what you have, will make that even worse because you have lost some valve lift (i.e. even shorter breaths).
There are no noticeable symptoms of this other than less than top potential torque and horsepower.
I do not know what heads you have, but when you install larger intake runner heads and larger carbs, there is a trade off...potential air flow vs. velocity. Velocity helps with hesitation and low end power. Air flow helps with high rpm power. There is a reason why drag cars idle at 2000rpm...they cannot run, atomize fuel, etc. at lower rpms. High performance engines are not efficient at low rpms. Hesitation can usually be tuned out of the carb using accelerator pump cams and nozzles, but not always.
That is why you need a plan and talk with someone who can verify the parts you are installing will work together to accomplish your goals. What you need for your motor and goals are totally different for what the other guys needs.
Having your mouth wide open and taking very short breaths. You are not starving your engine as much as not using it to its potential. A worn stock stock, if in fact that is what you have, will make that even worse because you have lost some valve lift (i.e. even shorter breaths).
There are no noticeable symptoms of this other than less than top potential torque and horsepower.
I do not know what heads you have, but when you install larger intake runner heads and larger carbs, there is a trade off...potential air flow vs. velocity. Velocity helps with hesitation and low end power. Air flow helps with high rpm power. There is a reason why drag cars idle at 2000rpm...they cannot run, atomize fuel, etc. at lower rpms. High performance engines are not efficient at low rpms. Hesitation can usually be tuned out of the carb using accelerator pump cams and nozzles, but not always.
That is why you need a plan and talk with someone who can verify the parts you are installing will work together to accomplish your goals. What you need for your motor and goals are totally different for what the other guys needs.
Last edited by urban_cowboy; Mar 23, 2009 at 11:47 AM.
Thread Starter
2nd Gear Member
Joined: Jul 2007
Posts: 322
From:
Thanks a lot, that is the kind of information I need.
I do feel a real loss of low-end torque and a lot of hesitations. This is not the way I like to drive my car (at least this one), my goal has never been to be the fastest on the road when I reach 5k RPM. I guess they were not completely aware of this when they told me that I did not have to change the cam with the performer heads.
If changing to a bigger cam solves this problem, I will not wait to do it.
I do feel a real loss of low-end torque and a lot of hesitations. This is not the way I like to drive my car (at least this one), my goal has never been to be the fastest on the road when I reach 5k RPM. I guess they were not completely aware of this when they told me that I did not have to change the cam with the performer heads.
If changing to a bigger cam solves this problem, I will not wait to do it.