351 Cleveland boss

gfi · #1 (**permalink**) 08-02-2003, 03:57 PM

Hi Folks:

I really have a dilemma and here's hoping someone can help. Just got a fresh 351 C Boss 850 Holley about 511 hp. Runs horrid: Only about 4.5 inches of vaccum at idle, have to feather to prevent from backfiring and get the idle up then it seems to get going ok. #2 problem is that I cannot seem to get the temp to stabilize. It just keeps climbing.

Any help or suggestions would be great.

Thanks

gary

Excaliber · #2 (**permalink**) 08-02-2003, 04:55 PM

Lumpy cam = low or no vacuum signal. Partial solution is mechanical advance only and "base timing" set up to a reasonable amount (14 or so).

Idle speed may have to be in the 1000 rpm range (or beter). The BIG heads on those engines were not low rpm happy, regardless of cam and intake. These are a high rpm motor.

Over heating? Don't know. but ignition and correct jets may help! Could be your running "lean".

Ernie

Junket · #3 (**permalink**) 08-02-2003, 05:20 PM

Gary sounds like a vacuum leak if you are runing at about 1000 RPM or so like Ernie says as far as the temp not stabilizing belive that would account for a wrong air fuel ratio it also run lean build to mutch heat at uper rpms also would cause back firing.
Ken

Dana E · #4 (**permalink**) 08-03-2003, 01:07 AM

Gary-

That 511 HP-is that a guess, or dyno verified? What's the compression ratio? Open, or closed chamber heads? Solid, or hydraulic cam? You would need a fairly "lumpy" cam for that HP. Try this: use some type of elecrtronic distributor with vacuum advance. Set it up with around 15 degrees initial/35 degrees total mechanical advance. Use an adjustable vacuum advance unit set to add another 10 degrees advance and connect it to a manifold vacuum source. Make sure there are no vacuum leaks and the valves and carb are adjusted correctly. Set the idle speed to 900-1100 rpm and check the idle vacuum. Depending on how low the idle vacuum is, you may need to change the power valves in the carb. Use ones that open 1.5" of vacuum lower than the idle speed vacuum (6" at idle=45 power valve). They need to be closed at idle or it will idle way too rich. As far as the running hot problem goes, hopefully the headgaskets are installed correctly and the restrictor is in place under the thermostat. Make sure you're using a Cleveland t/stat-it's different than a Windsor t/stat, which is what the parts guys will sell you-and it will overheat with the wrong style thermostat. Hope this helps.
Dana