I would say the 71 HO was a better running motor, as delivered from a dealership, than the RAIV. 71 HO was the fastest running engine between 71-74 series of Firebirds 455 ci engines-including the SD's(sorry SD guys). The RAIV's cam was too much for a 400 ci engine. when tuned correctly it can run well, but it was a service nightmare back in the day(from what I have heard)- had difficulty with idling/running rich therefore. All of us who have/or have had Pontiac 400 ci engines must admit they are sort of a disappointment. They just do not have the torque numbers that the 455's do. And the IV had less low end torque that a regular 400, it's power was in the upper RPM's, but as we all know street racing red light to red light (which is a beauty of Pontiac engines) was all in low end torque.. The 71 HO was the best of the 2nd gen 455's, even better than the SD in my opinion. The HO did not have the mystique of the Super Duty, but it was the best of its breed of engines. The last Pontiac engine that was pretty much bare engine without any pollution controls/restrictions. Yes the SD had great internals, but the HO's were sufficient. The 71 HO's engine originally came with Pontiacs 068 camshaft. The RAIV's 400ci engine cam was a bit much for the car, but as a rule.. moving up 10-20% in ci's allows moving up a step or two in camshaft. The HO will benefit and run well with a RAIV's camshaft or similar( a couple steps above the 068 which was used in the RAlll's(400 ci engines) as well as the stock HO).
If I were building a new 455 HO, I would use a roller valve train ,including a roller camshaft, would not mess with porting the heads, just gasket match and clean up any burrs, run as much compression as available(9.75-10.00) considering current gasoline. And for straight-line racing/red light to red light driving, the TH400 cannot be beat with a Muncie. Personally I prefer the Muncie, but an automatic is idiot(me) proof and always allows for lower et's.
This RAIV vs the 1971 HO engine rivalry has been going on for years. Even knew and saw a survivor RAIV where the original owner was embarrassed his car only had a 400 under the hood after the 1971 engines were released. He put 455 callouts on the scoop and rattle can painted the engine 71 HO color to hide the fact he only had a 400 ci engine. Truth be told, as delivered the RAIV was not the best running engine. With custom tweeking, could run ok, but the 71 HO was a fine engine as delivered and if anything was a bit under cammed. I have often suspected lowering the compression(which is commonly accepted as Pontiacs concession for the EPA) was not the only concession GM gave the EPA, but the cam choice were in fact what Pontiac did to appease the Fed's. The HO engine could have easily been delivered quite street able with a RAIV or similar camshaft. As someone has already stated, no substitute for cubic inches , and the '71 455 HO was the least messed with per pollution/gas buring regulations of the 71-74 455's.
So long answer to your question, in my opinion the '71 HO is the best running and easiest to improve upon without drastically changing( up compression and up cam) of these two engines . The RAIV is hindered by being a 400 ci based block. The HO is too similar to the RAIV(intake design,head design etc) which makes me thing Pontiacs engineers understood better than I do that the larger ci's was the answer for their performance round port program. Yes the RAIV has the mystique for their low production numbers, but short of 5000+ RPM racing, the IV was not as streetable as the HO-not by a long shot..
disclaimer
this is just one guys opinion, I do not portent to be the tree of knowledge when it comes to Pontiacs, so I could be wrong. This is just y opinion. Oh, and I have no malicious intentions here and apologize if my post offends any members of this board- that is not my intention.
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