Thread: LT1 or...

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A roller-ready block would have the tops of the lifter bores machined flat to accept dogbones. If the tops of the lifter bores are still as-cast, then it is a flat tappet block.

There are fellows building Gen I flat tappet motors every day, but it is not the hot tip any longer. We have seen failure after failure and now pretty much try to suggest a Gen I roller block to anyone who asks. Specifically, the 350 Vortec 5700 RPO L31 motor which came in '96 to '00 Chevy trucks and vans. Those motors would have the much sought after Vortec heads, so you could have roller cam and good heads in the same package. Although the wrecking yards are onto this scheme, many times you can find the motors on craigslist or other advertising medium for a reasonable amount of money. I would still pay up to about $400 for one, less the intake but otherwise complete pan to valve covers and with spider, dogbones and roller lifters. The heads will need some work for a performance application as the valve lift is limited to about 0.430" with the stock arrangement. The bottom of the valve retainer hits the top of the valve guide seal with lifts beyond stock. Do some searching and you will find the alterations necessary to hot rod these heads.

Now, if you are the hard-headed type and just have to build a flat tappet motor, then here is a list of failures to fix....
http://www.crankshaftcoalition.com/w...ips_and_tricks

There are roller 305 motors out there also, so check the head casting numbers before you lay down the long green for a motor. Cylinder head numbers 12558062 and 10239906 are the only two numbers used on L31 Vortec 350 heads.

You'll have to talk with some of the other fellows on this board about the Gen II LT1 motors. I have not built one. If I were going to build anything more radical than a late Gen I Vortec motor, it would be an LS motor.