I am researching my Buick 455 engine and I am getting more and more confused. There seems to have been 3 Buick 455 engine models available in 1970 according to the Buick Chassis Service Manual. These have the engine codes SR, SS and SF. The main specifications for them can be summarized as SR: 350HP@4600 RPM, 510 lbs-ft@2600 RPM 10.0:1 compression ratio SS: 360HP@4600 RPM, 510 lbs-ft@2600 RPM, 10.5:1 compression ratio (Stage 1) SF: 370HP@4600 RPM, 510 lbs-ft@2800 RPM, 10.0:1 compression ratio Engine SR has the lowest power output of 450HP at a compression ratio of 10.0:1. Then engine code SS denotes "Stage 1" in the Service Manual and outputs 460HP at 10.5:1 in compression. The Stage 1 is supposed to be some tune-up kit with larger valves, hotter cams etc if I understand it correctly. Here is a picture of what the larger valves are supposed to look like: http://www.stage1registry.com/stage1info.html Also with chromed valve covers so off course it should sling out a few more horses. But then we have the SF, which is the engine I have. The compression ratio is lowered to 10.0:1 again and the machine is supposed to output 370HP. That is 10HP more than Stage 1 (without chrome even)! There is a lot of information on Stage 1, here is even one stock version in a dyno: http://www.stage1registry.com/stage1info.html but I haven't found anything yet on the SF. What did they do to SF to make it crank out more power? Peak torque comes in a bit later, and the power rating implies higher torque at 4600 RPM. So it seems the torque curve might be shifted upwards a bit? Could that mean the same heads as the Stage 1, but an even hotter cam perhaps? What cars did the SF usually go in? Could you order it for any Buick car at the time? I guess this is anyone's guess, but why didn't Buick make the already talked up Stage 1 the most powerful? Also I hope this is not a typo in Buick's documentation, because otherwise I have the hottest stock engine Buick ever made in my car I got all the above specs from the Buick Chassis Service Manual section 60-41 (or see https://www.teambuick.com/reference/library/70_chassis/files/60-b.php). This information is mirrored here: https://www.teambuick.com/reference/us_35-76.php
So there has already been a long discussion on this forum regarding the subject: https://www.v8buick.com/index.php?threads/sr-code-sf-code-455s-whats-the-difference.103943/ No conclusion yet in that thread though. Some people seem to have found that the SR and SF had different cams at least. People in the thread say the SR and SF had the same valves, no real evidence for this yet though. There are widespread speculations online that power output numbers were tampered with to lower car insurance costs and for cars to qualify certain race competitions which had certain power/weight ratio classes. See for instance here: https://www.motortrend.com/features...ctory-underrating-muscle-car-power-1960s-1970. A quote from the article reads I cannot find the issue of MCR that is quoted unfortunately, would be interesting to read the full article. But if the SS (Stage 1) output 372HP in a dyno session, one almost wonders if they in fact exaggerated the SF specs a bit. If it is in fact true that the SF and SR are equal, as some people claim... Then there is this guy who measures over 400HP on a stock SS (Stage 1) 455 on a dyno: Gosh, maybe this will be one of those unsolved mysteries of the world. We can at least be sure that all of these machines have a lot of omph
