Have you succesfully put a bigger cam in a SBC with T.B.I.?

Chevy_Finatic79 · 10-22-2009, 08:46 AM

hey everyone I know its been ages since i been on the site ( I appologize) just been so busy workin on import cars i had to leave trucks alone for awhile. any way here we go

i want to know if anyone on the site has succesfully put a bigger than stock cam in thier throttle body fuel injected SmallBlock pre vortec and had no problems. not to be rude but i dont want to hear about a carbeb engine that wont help me at all they arent controlled by a computer

My problem according to my engine builder is vaccuum he says I need to drill holes in my butterfly's to create what he calls auxilliry air bleeds to smooth out my idle. because with the bigger cam i have the Idle Air control valve wont operate correctly it's always searching for the correct vaccuum making it rev then bog and so on.

remember this is only at idle I am talking about
I only notice it doing this in drive stopped at a light not in park it idles just fine in park. so before i drill holes and possibly spend the whole day with this i want to know if any of you had encounterd this before

mudseeker · 10-22-2009, 08:54 AM

you need someone to burn a new prom for you. drilling holes will not fix it and will only cuase problems due to more air entering the engine and your TPS staying the same value.

silverhairdeere · 10-22-2009, 08:58 AM

if this is a big cam , you may have to go to a high stall torque converter , i had to in my 70 nova , back in my racing days .

shd

Chevy_Finatic79 · 10-22-2009, 09:06 AM

well thats the thing hes saying the more air makes up for the vaccuum loss and everything esle goes back to operating as it should

by the way my motor is a 70's 350 block with a T.B.I. adapter plate controlled under stock 90 suburban computer and wiring

Chevy_Finatic79 · 10-22-2009, 09:14 AM

My cam is the second from the top of the list the first one is stock. my cam is not wild just the next size up

Chevy_Finatic79 · 10-22-2009, 12:00 PM

what does a stall converter have do with smooth idle? as far as i know a stall convertor doesnt allow the trans to engage until a certain rpm.

my problem isnt while moving
after 1100rpm the motor runs fine which is about where it idles in park and about half that in drive which is where i have the problem

IN DRIVE STOPPED AT A LIGHT WITH MY FOOT ON THE BRAKE IT SURGES

silverhairdeere · 10-22-2009, 01:08 PM

Quote:

Originally Posted by Chevy_Finatic79

what does a stall converter have do with smooth idle? as far as i know a stall convertor doesnt allow the trans to engage until a certain rpm.

my problem isnt while moving
after 1100rpm the motor runs fine which is about where it idles in park and about half that in drive which is where i have the problem

IN DRIVE STOPPED AT A LIGHT WITH MY FOOT ON THE BRAKE IT SURGES

a stock converter locks up at soon as it is put in gear draging your rpm down , a higher stall converter won't engage till a higher rpm , allowing the trans to slip at a lower rpm till you give it gas , just don't go to wild on the stall speed on a street engine , you will need a big trans cooler , the other choise is a different cam like maybe noumber 3 .

shd

mudseeker · 10-22-2009, 01:22 PM

get a new prom. your computer does not know that you have a bigger cam in the engine. 10* difference in lift and duration is a big deal for an engine. your engine is sucking in more air and your injector pulse width needs to be adjusted to compensate. you may also need to adjust your timing. this is why your IAC is going crazy.

Chevy_Finatic79 · 10-22-2009, 01:30 PM

i dont know who burns proms around here in lincoln ne and that sound alot more expensive than drilling holes for free. cant think of the guys name on here that used to burn proms but he said it wasnt worth it and never saw a difference after he burned them

sneekysportsman thats the guy

silverhairdeere · 10-22-2009, 01:32 PM

Quote:

Originally Posted by mudseeker

get a new prom. your computer does not know that you have a bigger cam in the engine. 10* difference in lift and duration is a big deal for an engine. your engine is sucking in more air and your injector pulse width needs to be adjusted to compensate. you may also need to adjust your timing. this is why your IAC is going crazy.

yea your right . i can't get my head out of the 70's

shd

10-22-2009, 08:46 AM	#1
Chevy_Finatic79 Senior Member Join Date: Mar 2008 Location: Lincoln NE Posts: 478	Have you succesfully put a bigger cam in a SBC with T.B.I.? hey everyone I know its been ages since i been on the site ( I appologize) just been so busy workin on import cars i had to leave trucks alone for awhile. any way here we go i want to know if anyone on the site has succesfully put a bigger than stock cam in thier throttle body fuel injected SmallBlock pre vortec and had no problems. not to be rude but i dont want to hear about a carbeb engine that wont help me at all they arent controlled by a computer My problem according to my engine builder is vaccuum he says I need to drill holes in my butterfly's to create what he calls auxilliry air bleeds to smooth out my idle. because with the bigger cam i have the Idle Air control valve wont operate correctly it's always searching for the correct vaccuum making it rev then bog and so on. remember this is only at idle I am talking about I only notice it doing this in drive stopped at a light not in park it idles just fine in park. so before i drill holes and possibly spend the whole day with this i want to know if any of you had encounterd this before __________________ "She's gonna Freak when she see's my wheels" 85' Chevy C-10 Longbox (Rat) TBI 327 Cu.In./THM350 90' Chevy Suburban 4x4 TBI 350 Cu.In./700R4 http://www.truckforum.org/forums/truck-pictures-176.htm

10-22-2009, 08:54 AM	#2
mudseeker Senior Moderator Join Date: Feb 2006 Location: michigan Posts: 6,376	you need someone to burn a new prom for you. drilling holes will not fix it and will only cuase problems due to more air entering the engine and your TPS staying the same value. __________________ i'd rather be hunting

10-22-2009, 09:06 AM	#4
Chevy_Finatic79 Senior Member Join Date: Mar 2008 Location: Lincoln NE Posts: 478	well thats the thing hes saying the more air makes up for the vaccuum loss and everything esle goes back to operating as it should by the way my motor is a 70's 350 block with a T.B.I. adapter plate controlled under stock 90 suburban computer and wiring __________________ "She's gonna Freak when she see's my wheels" 85' Chevy C-10 Longbox (Rat) TBI 327 Cu.In./THM350 90' Chevy Suburban 4x4 TBI 350 Cu.In./700R4 http://www.truckforum.org/forums/truck-pictures-176.htm

10-22-2009, 09:14 AM	#5
Chevy_Finatic79 Senior Member Join Date: Mar 2008 Location: Lincoln NE Posts: 478	My cam is the second from the top of the list the first one is stock. my cam is not wild just the next size up __________________ "She's gonna Freak when she see's my wheels" 85' Chevy C-10 Longbox (Rat) TBI 327 Cu.In./THM350 90' Chevy Suburban 4x4 TBI 350 Cu.In./700R4 http://www.truckforum.org/forums/truck-pictures-176.htm

10-22-2009, 12:00 PM	#6
Chevy_Finatic79 Senior Member Join Date: Mar 2008 Location: Lincoln NE Posts: 478	what does a stall converter have do with smooth idle? as far as i know a stall convertor doesnt allow the trans to engage until a certain rpm. my problem isnt while moving after 1100rpm the motor runs fine which is about where it idles in park and about half that in drive which is where i have the problem IN DRIVE STOPPED AT A LIGHT WITH MY FOOT ON THE BRAKE IT SURGES __________________ "She's gonna Freak when she see's my wheels" 85' Chevy C-10 Longbox (Rat) TBI 327 Cu.In./THM350 90' Chevy Suburban 4x4 TBI 350 Cu.In./700R4 http://www.truckforum.org/forums/truck-pictures-176.htm

10-22-2009, 08:58 AM	#3
silverhairdeere Senior Member Join Date: Feb 2008 Location: land between the lakes tn Posts: 1,184	if this is a big cam , you may have to go to a high stall torque converter , i had to in my 70 nova , back in my racing days . shd

10-22-2009, 01:22 PM	#8
mudseeker Senior Moderator Join Date: Feb 2006 Location: michigan Posts: 6,376	get a new prom. your computer does not know that you have a bigger cam in the engine. 10* difference in lift and duration is a big deal for an engine. your engine is sucking in more air and your injector pulse width needs to be adjusted to compensate. you may also need to adjust your timing. this is why your IAC is going crazy. __________________ i'd rather be hunting

10-22-2009, 01:30 PM	#9
Chevy_Finatic79 Senior Member Join Date: Mar 2008 Location: Lincoln NE Posts: 478	i dont know who burns proms around here in lincoln ne and that sound alot more expensive than drilling holes for free. cant think of the guys name on here that used to burn proms but he said it wasnt worth it and never saw a difference after he burned them sneekysportsman thats the guy __________________ "She's gonna Freak when she see's my wheels" 85' Chevy C-10 Longbox (Rat) TBI 327 Cu.In./THM350 90' Chevy Suburban 4x4 TBI 350 Cu.In./700R4 http://www.truckforum.org/forums/truck-pictures-176.htm

Thread Tools	Search this Thread
Show Printable Version Email this Page	Search this Thread: Advanced Search

Similar Threads
Thread	Thread Starter	Forum	Replies	Last Post
Bigger alt	silverChevy79	Chevy Truck Forum	2	10-16-2009 09:16 PM
Bigger tires, please help!!!	Brash	GMC Truck Forum	5	07-23-2009 12:51 PM
will bigger springs lift it?	chevy5	Chevy Truck Forum	21	02-20-2007 10:50 AM
Motor Rebuild... Going bigger??	Ozymandias	Chevy Truck Forum	2	09-22-2005 03:04 PM
want to go bigger	richardhead84	Chevy Truck Forum	1	04-30-2005 07:57 PM