Seems that your in high demand today.

I know that running a longer duration cam in a 350 tbi combo causes some problems with idle and fuel settings. I know that getting the fuel settings right takes chip changes.

My question is, how can you compensate for low vacuum at idle causing problems with the map sensor.

[This message has been edited by steve8586iroc (edited March 26, 2001).]

 

im not fast broker, but i run a combo with low idle vacuum (14"-15"). Theres no real trick to it you just need to tune the chip. the fuel and spark is pretty easy to get nailed what makes the idle crappy are the stock IAC commands. They can make your car perpetually idle high no matter what and "hunt" for idle speed. There are articles on the net about what you need to do when you get to this point though.

 

Pablo is right. PROM changes are necessary BUT mainly if you use a big of a cam along with other config changes, like heads intake, exhaust. If just cam/intake, you COULD be ok with just a mellow cam (204deg) and FP adjustments and timing advanced a bit.

For a 350, a 204deg intake cam (.450"/.470" lift) will/can EASILY (if matched components) get 300-320hp and will pull 19" of vac, or so This mellow cam will not effect you MAP/fuel systems too bad in a basically stock configured 350 but the OEM spark curves leave LOTS to be desired. If you are using other cam/heads/exhaust, you REALLY need a new PROM. If jsut a cam change but keeping heads/exhaust/egr, you can live with it.

I had a 194/214 cam in my (modded) 350 for a while and it pulled 21.5" vacuum at 600rpm idle and made 245 TBI Hp with PROM changes!!! But, my motor is in good shape.

Pablo's cam is a 214deg intake and will pull about 17" in a HEALTHY 350cid, he has a 305. You can get EASILY 320-340hp out of a PERFECTLY setup/matched 350cid with a 214/224 .442"/.460" generic SIS cam. Done it several times, as have others. You might as "who others?". How about GM as an example? Do you trust them? Their GM 330hp crate motor has a 212/222 .435"/.460" cam to make it's 330hp and trust me, that cam SUCKS!

You only need a Performer level intake manifold to make these lower power levels as the RPM/type manifold's runner size is JUST a little too big for these rpms/torque levels. And don't use ANY single plane manifold on a motor of thes power levels, EFI or not.


Again, I cannot stress enough how you MUST match the intake/head/cam/CompressionRatio/exhaust combo or you will need overkill in components somewhere to make up for the mismatch. Most people use too big of a cam to make up the mismatch, which is the absolute worst thing you can do when building an engine and just compounds the mismatch and leads to throttle response problems and weird driveability and SEVERE LACK OF LOW END!

[This message has been edited by FastBroker (edited March 27, 2001).]