I'm planning on a build with a tbi '7747 355 but have no clue what cam to run.

Heres the engine specs,

355, 9:1, Flat top pistons, Holley 670cfm tbi, HOlley intake, AFR 180cc 75cc eliminator heads, 3" exhaust, and I'm using the pro prominator.

I currently have that motor running 10:1 with camel humps and a l-79 (221/221-.447/.447-114 ) cam and am having some serious problems even getting it too run. It may be that I haven't logged it long enough to get decent tuning info but MAP numbers are real high 90 kpa at times from idle to 2500 rpm. I can't even get it too idle on it's own... It'll run but will stall out after about a minute if I'm not on the throttle. Should I just keep it running until I get enough log info. (7747 is SLOW) Is this the old cam or is something else wrong?

Anyways I will be going to the afr's, lower compression ratio and different cam soon and want to know what's the best cam for low end tq and decent hp that will get along with my computer?

This is a 5000LB K5 blazer so low end torque is important. I don't want the hp to be cut down too much though. Also I'm trying to pass California emissions.

Sorry for all the questions.

Thanks in advance.

 

Quote:
It may be that I haven't logged it long enough to get decent tuning info but MAP numbers are real high 90 kpa at times from idle to 2500 rpm. I can't even get it too idle on it's own... It'll run but will stall out after about a minute if I'm not on the throttle.

I dont belive you should see 90 KPA unless the throttle is opened quite a bit. test MAP sensor.

Any open ports on the TBI unit? Vac leaks? TBI base gasket leak?

I would turn the throttle stop screw(TSS) a bit to get it to idle and at least not die. then later fine tune idle speed. That should allow you to drive and datalog to see what sensors are seeing..

 

If you are going to be putting those heads and a different cam into it. I would suggest converting to the Dynamic EFI ebl flash. Its a direct swap for the 7747 and is way easier and faster to tune with. Plus no chip swapping etc. Just my thoughts

 

The throttle is open quite a bit... otherwise it dies. If I hold the throttle in one spot it will die. I have to baby it and it will barely move without almost stalling.

I might have the vaccuum lines on the holley tbi crossed up. Anyone have a diagram for the holley 670cfm tbi?

Also how would I go about testing the map sensor?

I would like to go to the ebl setup but I paid 275 for the prominator right before the ebl went to flash. What would I be able to sell the pro prominaotr for? I bought the LED switch also. http://www.speedtronics.net/aboutprominator.asp

 

I believe there is an OHM test. search. In your datalogs key on engine off you should see 95-100 MAP. Idle and I understand that is problematic I would expect 30-40 MAP. But if you idle is not cooperating I dont know what the MAP would read.

I would check Holley web site for vac lines instructions. There are instructions on this site that should be of help. search. I will locate on another site the stock diagrams. Should be pretty much same. My car in barn for a few more weeks of I could take a look. Maybe I have a pic of my 7.4L lines?

 

PCV is attached to the large port in front of TBI. My MAP is at rear of TBI unit. My VAFPR goes to rear of manifold where brake booster line attaches with a threaded nipple(not TBI port).

 

http://z28boy.cz28.com/main.htm

note vac port on rear of unit for MAP. rest of mine are capped. last spring I noted one cap was cracked and leaking. a 50 cent fix improved idle !