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Hi all, i have a 95 GMC Sierra k1500 five speed manual trans. Factory motor was 305, upgrade to 350 vortec crate motor. I want to keep it tbi and have the tbi to vortec intake, I cannot return this intake, my question is what cam and roller rockers upgrade can i use with tbi? I do not want to change the springs. I know ill have to have the chip flashed. Motor is l31.
 

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The factory tbi can not do this without alot of headaches.
You would be better off using a aftermarket tbi unit that you could adjust for the cam and heads.
Now megasquirt(ms2)"diyautotune" is the first company that comes across my mind letting you run the factory tbi and modify the pulses to provide the proper air fuel ratio. Now the tbi distributor can also work with this megasquirt.

I would search the megasquirt forums. There is probally a couple people who have done something similar already with downloadable fuel tables which will make this as plug and play as possible.
 

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Contact Howell Engine Development and ask them about cam recommendations---a guy there designed the GM TBI system
 

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For stock standalone tbi setups l use this Michigan based company;


They can set you up with a standalone harness and you can ship them your ecm or just buy another to save time.

They also can modify the ecm and harness to run a wide variety of engines at diffrent power levels.

They are a proven company where you get your moneys worth.
 

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Just getting from the 305 to the 350 TBI would require a chip out of a 350 while the factory ECM has enough learn for wear compensation, is not capable of bridging a 305 to a 350. However the learn capability of a 350 TBI computer chip is sufficient to bridge a 350 LO5 , TBI to a fresh L31, 350 with a factory TBI conversion, but that’s it. The L31 roller cam is quite similar in timing to the old 300 horse cam used in the high compression 327 and the lower compression 350 both with 4bbl carb back in the late 60’s early 70’s. Going beyond that takes a custom chip in the TBI computer.

The L31 head doesn’t like much lift somewhere between .45 and .47 inch the bottom of the spring retainer gets hard slammed into the top of the valve guide. There are two solutions one is to mill the guide down till it provides enough clearance, the second is to convert to beehive springs and their attentive Company Cams 787-16 retainer that bridges the metric spring to the US size 11/32 dia valve stem. GM metric parts are for an 8mm stem and will not seat the stem locks properly on an 11/32 stem.

There are some GM roller cams that are quite compatible in a 350 with Vortec heads and a original GM TBI. The cam the L31 comes with is 255/190*degrees intake with .412 lift at the valve using a 1.5 rocker; exhaust is 266/195* degrees with .428 inches of lift at the valve on 1.5 rocker the LSA is 110.5 degrees: ** notes duration at .050 inch lift. Your TBI cam times at .050 with 166/175 degrees using .383/.402 valve lift, so it is a lot milder than even the mild L31 cam.

Probably the most cam bang for factory TBI is the 1995-97 LT1 cam part 12551705 it times at point oh-fifty with 201/208 degrees using .447/.459 valve lift on an LSA of 117 degrees. This cam is very factory TBI friendly without having to push chips to and beyond the systems design limits. Messing with cams in your situation can lead you down a very complicated and expensive path as the factory TBI is both air and fuel flow limited and you will quickly play into a situation where your TBI and your fuel supply system is maxed out. These are not like carburetors where we think of performance in terms CFM. With fuel injection CFM is only an air flow condition, the fuel flow is controlled by injector size, fuel delivery pressure and duty cycle time on the injectors. This gets technically messy and expensive very quickly. Plus the heyday of messing with factory TBI was a long time ago, the number and quality of practioners has declined a lot in the 21st century.


Bogie
 
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