trans_am_ta_84

hey guys... what kind of cam do you guys think would be nice to use in my car:

350 tbi
bored .030 over
305 tpi heads
lt1 cam (in it right now)
edelbrock performer tbi intake
flowtech headers

i want my car to have a kinda loppy cam... i haven't put the motor together yet but i do have the lt1 cam.. dunno how it will be? thanks

ShiftyCapone

iTrader: (7)

Lopey and TBI do not mix. if you want a slight lope you will have to find a cam with around 110 or 111 LSA. Unless you have done some work to those heads the cam you choose cannot be any larger than the LT1 cam in there now.

steve8586iroc

Look at more duration instead of more lift. Unless the heads have the larger 1.94" valves installed in them you need to concentrate on low to midrange torque and power. The small valves in stock 305tpi heads will be the limiting factor. You will also be running about 1 point more compression than you would with 350 heads so you might have some timing issues to be concerned about. Then there is tuning the prom to get everything working properly. Other than that you should have a nice running engine.

Steve

91 GTA Ramair2

wow!! who say's you can't run a big cam in a TBI engine??

the Amx has the commander 950 4bbl tbi setup on it, with a 307*dur.625lift cam, and it run's just fine with plenty of rumpity rump to it's idle.......

MPI in my 91 GTA dose fine with the 406 with the 292*dur.580lift cam idles nice and choppy.
Don't get me wrong it ain't as choppy as if they was carbbed.

gen3z

lobe seperation has nothing to do with a choppy idle some of the factory 305/350s came with a 109 lobe center,duration causes the choppy/lopey idle.....i have had some tbi 350/383s with 114 down to 110 lobes with 224 up to 236 degrees of duration its all in the chip& tuning.

ShiftyCapone

iTrader: (7)

Oh yes it does. You are right that duration does but so does LSA. LSA will make the biggest difference for EFI cars. The 109 LSA's you talk about are for carb applications. Put a 109 LSA in a TBI/TPI/LT1/LS1 and watch it try to idle, even with a custom tune.

AJ_92RS

The LB9 from 1986 to 1992 came with 109* LSA.

See for yourself.

https://www.thirdgen.org/newdesign/tech/techdb.shtml

The thing you're looking for with EFI is less overlap. Depending on what the duration is will determine what LSA is needed. To say "109* LSA won't work" or "Only cams with 112* or more LSA will work" are both vague statements.

All that needs to be done is get a cam that is specifically designed for EFI and there won't be a problem.

91 GTA Ramair2

a 305TBI will kick nice woth some 3.73 gear's......

my 91 GTA had an old twice baked 350TBI it pulled 14.80's with 3.73 gear's

ShiftyCapone

iTrader: (7)

Yea you are right but 95% of cams that are for EFI come with high LSA's. For the novice cam buyers it is a good principal to go by.

BronYrAur

iTrader: (1)

Basically, if duration is very low, as in the stock cams listed above with 109* lobe separations, you can have a low LSA; but if you get a cam more in the duration range of say LT1 cam to ZZ4 to LT4 HOT CAM then you would want a LSA of 112 or higher. We can run well on a small lobe separation because we have super low duration stock. You have to compare both duration and LSA and find the happy point where its EFI friendly to pull enough vacuum.

BMmonteSS

I think the expression that "tbi and lopey cams should not mix" needs to be followed by "without chip tuning". I'm running a 216 228 extreme energy 4x4 with a 111 lobe sep. It has a nice little lope nothing too wild but just right for a daily driver. It idles with about 50 kpa plus or minus about 5kpa worth of float because of the cam. You can run something much meaner without too much problems considering the nature of the beast.

Now the catch is YES it does take alot more tuning than a cam with 112 or 114 lobe sep. TBI is special because unlike mpi you have to fool with the delay that it takes for the fuel to get from the TB to the combustion chamber which can take a long time with a lopy cam. There are tables in the chip to allow you to tune around this. Other than that there is nothing different between TBI and a mpi setup with a big cam. Traxion is useing a cam with around 240 deg of duration, he idles with about 70 kpa and the car drives fine.

99% of the cpu friendly cams out there are designed with the idea of the end user not being able to tune their car. They are trying to make the cam behave with a stock tune. TBI doesn't tollerate this as well as other types of injection because of the issues mention earlier, I think this is why everyone assumes that TBI won't work with a lopey cam.