Replacing a camshaft with classic FAST system...

[Blown86GT]

I replaced the original camshaft in my 408 with one supposedly identical in specs (the original cam had lobes going flat and was defective). The car ran great with the original cam but with the "new" cam, it runs terrible using the same tune.

After replacing/checking every component on the car, I had a hunch the camshaft wasn't exactly the same. So I sent it off to comp cams to have them respec it and sure enough, all though it is close...the specs are off. The duration on the inake and exhaust is 3 to 4 degrees off as is the lift. (original cam was 232/240, "new" cam is 229/236 duration. Lift went from .355/.360 to .349/.355) Could this explain why the car runs so terrible now( using the original tune)? Is a new tune in order?

 

[S2V6RACER]

Most likely your MAP is different with the new cam. I'd say barring no mechanical issues you need to re-tune the engine.

 

[TurboTR]

Yes, speed/density is very sensitive to changes like this, as youve found.

TurboTR

 

[turbolou]

Reply

wouldn't correction factors give an indication of the difference. Then tune off that. cam isn't that much more different, check engine vacuum. Is there enough to operate map sensor. Is it steady, are the valves too tight,Cam indexed correctly. Were there any other issues that could throw off tune. no expert here but that would be a place to start before going into paralysis by analysis

 

[Blown86GT]

Thanks for all the replies! After several years of troubleshooting (and headaches, temptation to sell, etc. etc.) I finally have figured out the problem. It turns out the cam I received didn't have the same amount of advance ground into it as the original...so installing it as I did the original resulted in 4 more degrees of advance than the original. So much for "an identical grind!"

I degreed the cam, and reinstalled it correctly...and the car runs like a champ! Again thanks for the help guys! Now I can finally enjoy my car again!