i have 1976 455 4 speed car how do i know if it is a sd 455 or 455 ho......
First, welcome to
78TA.com! Post up some pics of your ride -- we'd love to see it! Don't be bashful! And if you need help just ask -- we'll help out!
Now...to your question...
The way to tell an SD or HO engine is to look at the exhaust manifolds. If the engine has exhaust manifolds that look like these below, then you need to see if the exhaust ports are round.
The ones in the pics are technically "RAIII" manifolds, which fit a D-port head -- but if the overall shape of yours is similar then you *might* have round ports. If your exhaust manifolds don't look anything like these, then you do NOT have an SD or HO engine.
But...even if you do NOT have an SD or HO engine...AND your numbers match...then you still have a pretty desirable car. The ONLY way you could get a 455 from the factory in 1976 was to buy a 4 speed and order the optional engine -- and from the sound of it, that's what you may well have. Post up the first numbers of the VIN (just put XXXXX in the last 5 digits -- we don't need your serial number) and we can tell you what it's supposed to have under the hood.