I am pretty sure i know the answer but are the starters the same ones? The reason i am asking is i have a 4bolt main motor i am building and i have no starter. Are the starters interchangable either way?

 

Yes they are interchangeable.

 

The 4-bolt block is a 2 bolt block with a few extra holes drilled in it for the mains, same casting.

 

To fully answer this question, you need to dig a little deeper than the replys you've received above.

The static compression ratio on the 5.7L LT1 motor was 10.4 to 1. On its LT4 counterpart is was 10.8 to 1.

Since the electrical performance of a starter motor is determined by the cylinder cranking pressure it must overcome to actually crank the motor at a minimum speed, (usually 50-60 RPM), the LT4 starter should be a "higher torque/higher load" starter.

Phyisically, (i.e. outside dimension wise), the starters ARE interchangable, as was indicated in the above posts, but .......... check on Shoebox's web site, and if GM shows two (2) different part numbers for these starters ............ the LT4 starter will be a higher torque starter than the LT1.

 

I agree that the compression ratio for the LT4 was higher. It's my understanding that the LT1 compression ratio was 10.4:1 while the LT4 was 10.8:1.

 

The iron head LT1 was 10:1 the aluminum head LT1 was 10.4 the LT4 was 10.8.
Practical experience is that the LT1 starter has no problem with over 12:1 and 245psi cranking compression. If your's has trouble upgrade the cables before "upgrading" the starter.

To worry about needing a higher power starter without first upgrading the power cable is like taking a stock car and doing engine upgrades with factory intake tract and exhaust.