Does a stock '73 455 (without the pollution junk) put out about the same hp as a stock '70 SF 455? Any issues with putting a '73 455 in a '68 GS convertible?
The 1973 455 has lower compression (~1.5:1 lower) than the 1970. There will be a small loss of power related to that. The cam profile may also be a bit tamer. It does, however, have a bigger cfm carb - assuming that it hasn't been changed. There shouldn't be any big problems replacing the 400 in your GS. There are two different water pumps, one with a long nose or a short nose. This could effect the pullies lining up and how far your fan sticks in the shroud.
Adjusting for the gross hp to SAE hp change in convention from 70 to 73 there is about a 40 hp reduction. A carb rebuilder that I know who is a Buick Drag racer says that in his head to head tests on the same car the same day the 750 CFM q jet and the 800 cfm q jet result in no change in performance on the track.
There is close to 2. difference in compression 8.5 to 1, compared to the 10.5 to 1, 70 moter, the 70 pistons have a 25 cc dish and the 73 i think are about 43 cc, so i would guess at least 60 H/P difference, but a huge drop in torque, i would say 100 ft lbs. also the 800 carb only helps if your turning over 5500 rpm, just my 2 cents
1 point of compression is worth about 3-4% in power. An 8.5 to 1 and a 10.5 to 1 motor have about 8% difference in HP. So a 455 rated at 365 HP with 10.5 to 1 will at 335 HP with 8.5 to 1. Now, how the engines were rated and tested by the manufacturer is another story....... :laugh:
Kelly, I thought the standard valve 70 motor was 10:1 and the Stage 1 valved heads saw a little bit of an increase due to the valves taking up more of the chamber space, and they were closer to 10.5:1? o No:
Steve, Years ago, someone actually cc'ed a stock motor. The compression was actually closer to 9.8:1 Buick fibbed a little. o No:
what ever it is, isnt the real issue is loss of low and mid range torque. thats most impotant for a good street moter running a little more cam then stock, commpression = torque. to me tourque is more important then h/p in these moters. there are cars running deep in the 12's, and shifting below 5000 rpm
The whole compression thing is something I think about quite a bit! If I ever build the 455 I have, I want it to be pump gas for sure but don't want it to be a pig if you know what I mean!! I have been reading all about DCR and SCR and think I have a handle on what I can get away with as far as compression and intake closing etc. but keep thinking about something else. I have a friend with a bone stock 72GS 455 and it is a heavily optioned car that FLAT OUT ROCKS! Just makes me wonder if sometimes the compression benefit isn't a little over hyped at times?? On the other hand, the car could be a little down on low end torque and actually hook up better? I.m not talking about a race car here but for a nice street driven car, his 8.5-1 seems to scoot just fine! :3gears: Ken
Just because you have more torque than you need doesn't mean you have to use it. The best rpm for 'stock' Stage 1 cars was I beleive 2200 rpm in 1970. Idle in gear is ~600 rpm. So you aren't making max torque right away anyhow. 2200 rpm is pretty low in the powerband (some might call it 'subterranean' compared to many other muscle cars), but just because you can smoke the tires doesn't mean you have to. A little wheelspin is desireable, I'm told PS- "bone stock" and "heavily optioned" are mutually exclusive. You can't have have a heavily optioned bone stock car :TU:
I have about 11 to 1 comp. and with .373 gears i can get my car to go side ways on street tires at 30 mph, now thats fun!!!
Sure you can! Bone stock- as it came from the factory- doesn't mean less options- just unmolested. It could be a heavily optioned car that is completely unmodified. ________ THE VOLCANO VAPORIZER REVIEWS
Ken, My 71 GS455 was a stock shortblock car, with a reground cam and fresh, stock non-Stage heads. With just headers, Performer, and 3.42 posi, it ran consistent mid 13's. Although I put higher octane fuel in it, it could have ran on 87 octane. The Custom I have now is also low compression. I'm curious to see how it will do on low octane. Hopefully I'll get the gears/posi in this coming year to find out. I'd love to be in the 12's on 87 octane, if possible. Once I know something I'll post it, of course.
YEAH! What he said! Stock as in nothing in the drivtrain has been changed from the way it left the factory and heavily optioned as in ........well, not a stripped down model? Ken
So... since I started this thread... IF you could get a '73 455 delivered to your door, or a '70 455 600 miles away, for the same price, and you know nothing about either motor... What would you do? o No:
Well I would say that all depends on what you want, and what you plan on doing to the motor when you get it! If it's for a daily driver that you want to have run good but not looking for the best ET, then I would look into the local 1973. If you plan to build it up then the 70 would have better heads if you were going to use iron heads. If you are really going to build it up with aluminum heads then the 73 block had better oiling and a bigger pick-up tube but the 70 block could be drilled and a bigger pick-up installed. If you are hoping to just drop it in as-is and don't want to buy good fuel, then the 73. The 70 would need 93-94 octane and the timing may need backed off to keep it from pinging. You have a tough choice here for sure! Are both motors complete, or does one have more bolt-ons with it? Ken
A few more thoughts, 600 miles is a long way away and unless you can get some kind of deal, freight might be high on that one. The 70 engine would look a lot closer to what would be in the 68 because the 73 has the big tubes for the air pump in the intake manifold. If you want to fool someone into thinking it's stock, you'd have a hard time doing it with that 73 intake! Ken
Ken (or anyone else), I have an after market Edelbrock intake and carb that fits my '68 400. Will this intake and carb fit on the '73 455? Do I need to use the air pump? Gil
The '73 heads have holes for the air passages that mate up with the stock intake. The holes will need to be tapped and plugged to use your intake. I just used the stocker on my last 455('74 vintage).
