TransamGTA350

iTrader: (2)

Yes, stock computer and gauges will work. A stock L31 is close enough to a stock L98 that the stock chip would work. If you don’t connect the external egr pipe though, then you would need a custom chip to eliminate EGR or you will get a check engine light.

If you’re starting with a 305, you will need 350 injectors (22lb/hr) and a chip burned for those injectors.

if you swap the cam, I would do a custom chip to optimize for the configuration.

jasper21

I have read a couple conflicting things on the springs? Will the stock **SPRINGS and **CAM be ok with (running TUNED PORT INJECTION) ? Prolly goin to go with SCOGGINS DICKEY for the L31-r & lower vortec base, is there anything that I should replace/need while engine is out? I figured i would Source a 350 chip from a "Tuner" (L31 should be available with Vats, DELETE, Egr, Temp...since its so common a swap=try to avoid paying 2x)

Is there any kinda advice or certain things I should account for? (beside Knock, injectors, 350 chip) How about headers/exhaust, do they need to be a specifiic for L31 or...?

jasper21

I have read a couple conflicting things on the springs? Will the stock **SPRINGS and **CAM be ok with (running TUNED PORT INJECTION) ? Prolly goin to go with SCOGGINS DICKEY for the L31-r & lower vortec base, is there anything that I should replace/need while engine is out? I figured i would Source a 350 chip from a "Tuner" (L31 should be available with Vats, DELETE, Egr, Temp...since its so common a swap=try to avoid paying 2x)

Is there any kinda advice or certain things I should account for? (beside Knock, injectors, 350 chip) How about headers/exhaust, do they need to be a specifiic for L31 or...?

TransamGTA350

iTrader: (2)

The valve springs are matched to the cam, so if you leave the internals of the L31 engine alone, the springs will be fine. The stock L31 cam profile will work fine with the TPI. It is a little less aggressive than the L98 cam, but the better flowing Vortec heads make up for that, so the net is about the same as the stock L98 motor. In addition to the normal 305 to 350 conversion parts (injectors, knock sensor, chip/tune), there are a handful of small things you will need to do to adapt the newer L31 long block to the older TPI system, like swapping the timing cover, modify the ignition coil mounting bracket, external EGR pipe or EGR delete. If you are using stock exhaust manifolds, the most rearward manifold bolt on the passenger side exhaust manifold can't be installed because the Vortec heads don't have that extra bolt hole. Any SBC/Thirdgen headers will fit though since they don't use that extra bolt hole. It's the same basic small block architecture, just minor running changes GM made in the years after the thirdgens were built. This thread does a good job of describing the process.

Complete L31-R Swap Guide [91 TPI] - Third Generation F-Body Message Boards

KCG

iTrader: (1)

Just figured this out the hard way.
Has anyone here found a stock exhaust manifold that works on the passenger side?

TransamGTA350

iTrader: (2)

None that I am aware of. There are a couple of companies that make adapter plates. No idea how well they work, never tried them. Something like this, although these particular ones look to be currently out of stock.
Small Block Chevy Exhaust Header Adapter Plate | Top Street Performance - Free Shipping over $99

Others on this board have reported not using that last bolt and had no issues.

You could also swap the manifolds for headers.

dmccain

iTrader: (2)

I tried the aapter plate on my last Vortec head Thirdgen. Leaked, didn't fit well.. etc. Best thing to do is go with headers, good ones.

KCG

iTrader: (1)

I thought about making an adapter of some sort...
Thought about leaving it for about a second..even though its really thick material at that point, I'm not sure I could chance it.

thanks for replies so far