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tuning

 
300post
I love my Chevy Chevette!
Posts: 1
Joined: 03/13
Posted: 03/29/13 08:56 AM

will i ever be able to tune 200 runner heads on 350 sbc to operate at low rpm ? low end stumble addvise all over the board biger cam no smaller cam no smaller carb changed to smaller cam bigger and smaller intake and other way around maybe 200 runners wont work low rpm driveablity fooling my self switch to 170 or 180 runner ?  

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waynep712222
V-6 Camaros rule!
Posts: 122
Joined: 03/13
Posted: 03/29/13 11:11 AM

welcome to the forums..

can you post more info????

carb type.. and CFM..  and what mods you have made to it??

intake type?? and model number.. mods???

cam lift and duration or grind number..

compression ratio/ or cranking compression..

ignition type... points .. electronic.. how much initial and total.. and how much how soon..??
this can be done with an adjustable advance timing light.. an Tachometer and a vacuum gauge with a TEE...

what are your intake manifold vacuum readings in park... at idle in drive.. crusing down the highway at a steady speed???

transmission type and rear end gear ratio....   if its an automatic... stall speed??

rear tire height or roll out.. how many turns per mile...   cruising speed RPMs..


there are a few things that can improve low speed drivability...

install at least a cheep air fuel ratio display.. and since you probably have headers... a 3 wire oxygen sensor from a 94/95 chevy truck 5.7 application .. but install it thru the collector side or top if there is room..

watch the air fuel ratio as you are in idle..  during idle transition..  and during primary operation..   at cruise speed also..  when the engine is just running along at part throttle.. steady speed..

if it leans out.. coming off idle ... its might be easily fixed..  or at part throttle cruise...

read up on the idle transition circuits...  and post as much of the info i ask for... as there are some smart people here...  

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pepsi1
Big Block power for the win
Posts: 940
Joined: 03/11
Posted: 03/29/13 05:39 PM

Yeah I agree with Wayne:
The more information we have the better it will help you and help us. Be pecific it won;t hurt.

Bon  

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68scott385
I have an SS396 tatoo
Posts: 325
Joined: 07/09
Posted: 03/30/13 07:58 AM

Generally, big cam, big carb, and big cc/cfm ports won't idle well at production motor idle rpms. You'll have to raise the idle speed, to what depends on the parts in the combination and the application. At low engine speeds big ports don't create much velocity and therefore have a weak signal at the carb venturis, giving an air/fuel mixture that is inconsistant causing rough/irratic idle characteristics.

Be very sepcific, you don't have to give away any secrets but details help.

Are you runing an Edelbrock/Carter carb? They are very simplistic, easy to work on carbs but limited in the fine tuning department.  
68scott385 68scott385 68scott385

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pepsi1
Big Block power for the win
Posts: 940
Joined: 03/11
Posted: 03/30/13 03:53 PM

I just ran some figures.

You can get that engine to idle with the way you have it set up. The cam with a 1.5 rocker ratio you don't want high lift or a long duration cam.

Stay under .210/.213  duration. and a lift of .424/.450 the max lift. You don't want to smoother it with too much carburetor. IE 550cfm and have a proper tune at atleast 19* to 21* of vacuum.

Bob  

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pepsi1
Big Block power for the win
Posts: 940
Joined: 03/11
Posted: 03/30/13 03:54 PM

I just ran some figures.

You can get that engine to idle with the way you have it set up. The cam with a 1.5 rocker ratio you don't want high lift or a long duration cam.

Stay under .210/.213  duration. and a lift of .424/.450 the max lift. You don't want to smoother it with too much carburetor. IE 550cfm and have a proper tune at atleast 19* to 21* of vacuum.

Bob  

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