Cam shaft question
Thread Starter
Drifting
Joined: Feb 2013
Posts: 1,464
Likes: 48
Cam shaft question
Hello Everybody, I have a 1985 TPI stock 4 plus 3 Corvette I installed a larger cam the original is
202/216 @ 0.5
403/415 114.5 separation
The new cam is
212/226 @ 0.50
483/520 112 separation
1.5 rockers
Will this cam give me idle problems. The description, Summit Racing, says 1000 rpm to 5000 rpm.
The car is running like it has a vacuum leak.
Thank you for the help
202/216 @ 0.5
403/415 114.5 separation
The new cam is
212/226 @ 0.50
483/520 112 separation
1.5 rockers
Will this cam give me idle problems. The description, Summit Racing, says 1000 rpm to 5000 rpm.
The car is running like it has a vacuum leak.
Thank you for the help
Safety Car
Joined: Sep 2001
Posts: 4,157
Likes: 554
From: Glenbeulah Wi
It might, the stock tune will try and idle at 550 rpm and that may be too low for a smooth idle. Since you mentioned it make sure you do not have a vacuum leak and make sure your timing is correct. Does the car smooth out if you hold the throttle open enough to keep it at 700 rpm? You may need a tune, you may also want to set your minimum idle speed warmed up at 600 rpm and see how it works.
Last edited by bjankuski; Dec 26, 2019 at 07:51 AM.
Thread Starter
Drifting
Joined: Feb 2013
Posts: 1,464
Likes: 48
First thank you for the response. What I am asking is. Does the cam profile seem so radical that the car would have problems idling. I have a chip in the car that was supposed to be tuned for this cam. The Summit Racing profile says the cam is 1000 to 5000 rpm.
I think it will maintain a higher idle.
I am wondering if the valves are too tight. But, I had good compression when I assembled the motor
Thank you. I will forward your suggestion to my mechanic.
I think it will maintain a higher idle.
I am wondering if the valves are too tight. But, I had good compression when I assembled the motor
Thank you. I will forward your suggestion to my mechanic.
Drifting
Joined: Jun 2018
Posts: 1,678
Likes: 229
From: Michigan
When did you get the chip? Who burned it?
The target idle is set in the Chip. Once you got everything together, have you performed an IAC reset procedure? This is where you adjust base timing and the throttle stop screw, adjust the TPS, and verify counts at idle to ensure the ECM has control.
You said it idles like it has a vacuum leak, which means high RPM and lean. Is this correct?
As mentioned above, the person who burned your chip should have bumped your warm idle target up to 700-750RPMs. You can test this by the throttle stop screw. You should not leave it set open, but you can open the throttle stop screw far enough that the ECM will have 0 counts on the IAC and then just use it to achieve a smooth idle. Once you know the RPM, you can have this burned to the PROM. Don't forget to set the throttle stop screw back to an appropriate position. I like to see IAC counts between 20-50 when the engine is warm and transmission is in park. Should not matter if the target is 600/650/750. That is the base you are shooting for and you want to know the ECM has the ability to control it.
Melting Slicks
Joined: Aug 2003
Posts: 3,399
Likes: 394
From: Lakeville MI
85 4+3 bins (like HLP) already target 750 rpm for warm/hot idle. Later 4+3 bins target 700 rpm. Auto trans bins have the lower 550-575 rpm target idle.
The stated cam should idle fine at 750 rpm. Post a copy of your bin and a log of it running, if you can. It is likely that the spark advance table could use some work to add idle stability. Suggest you contact your tuner.
The stated cam should idle fine at 750 rpm. Post a copy of your bin and a log of it running, if you can. It is likely that the spark advance table could use some work to add idle stability. Suggest you contact your tuner.
Last edited by tequilaboy; Dec 26, 2019 at 11:00 AM.
Safety Car
Joined: Sep 2001
Posts: 4,157
Likes: 554
From: Glenbeulah Wi
First thank you for the response. What I am asking is. Does the cam profile seem so radical that the car would have problems idling. I have a chip in the car that was supposed to be tuned for this cam. The Summit Racing profile says the cam is 1000 to 5000 rpm.
I think it will maintain a higher idle.
I am wondering if the valves are too tight. But, I had good compression when I assembled the motor
Thank you. I will forward your suggestion to my mechanic.
I think it will maintain a higher idle.
I am wondering if the valves are too tight. But, I had good compression when I assembled the motor
Thank you. I will forward your suggestion to my mechanic.
Drifting
Joined: Jun 2018
Posts: 1,678
Likes: 229
From: Michigan
Thread Starter
Drifting
Joined: Feb 2013
Posts: 1,464
Likes: 48
Thank you all for your help.
one correction the 206/216 is the stock cam the the bigger 213/226 is the after market can. The IAC adjustment makes sense.
I am reading this on my phone at 4 AM . I hope to digest it better later today.
Thanks again
one correction the 206/216 is the stock cam the the bigger 213/226 is the after market can. The IAC adjustment makes sense.
I am reading this on my phone at 4 AM . I hope to digest it better later today.
Thanks again
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