1977 Scarab 300- twin 383 speed
 

Hello,

I will be going to look at a '77 Scarab 300 and it is claimed to be powered by twin 383s. As 383s and 350s look identical, and the only way to truly know which is which is to look at the bottom end of the engine, I am planning on judging the power of this boat by doing a full throttle pass.

The engines are currently claimed to be putting out 410HP each (which I believe to be a lofty estimate) but I am thinking that if the boat breaks into the 60s comfortably, I can be sure that they are at least well built 350s. It is my understanding that these boats ran ~55mph with the stock 350s.

I would like to hear opinions on what you think the boat should run (assuming a less than ideal setup) with the claimed power or at least the power of a moderate 383.

thanks,
jake

A 383 is a stroked 350, it was never a factory GM engine so there will be not way to tell if it's really a 383 other than measuring the stroke or getting a number off the crank.

Yes, I understand that, hence the reason I said they look identical and the only way to tell is to look at the bottom end of the engine. My question is, what speed should this hull run if the engine is as the owner claimed?

Well back in the day I had a '76 Scarab twin small blocks (280 TRS) with outside exhaust and best I seen was 58mph with clean bottom and 3 blade cleavers 21" pitch. My friend had the same with some minor mods and diff exhaust and best he seen was 61mph so my guess would be mid 60's with the right props.

Thanks for the info! That was basically my guess as well but it's good to hear of some real world numbers that help back my guess up. If the RPMs are correct and the boat is seeing anything less than 63-64mph, I will assume that it does not have 383s. Thanks again, and I will post an update after running the boat

Whether it is good built 350's or 383's it will probably only be 1 mph difference.You're only talking ~50 HP combined. Anything over 59 mph and I would consider them "built". I looked at a 300 with 280 small blocks and it was a 55 mph boat. 400HP/side should get get the boat to 63-65. My TRS Panther was 70 mph with merc 420's with a little work.

Good luck on your test!