Olds 455 build

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scarborough

Master Mechanic
Sep 30, 2016
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any opinions on how much hp a Olds 455 build can make using stock exhaust manifold and duals 2 inch pipe
 

69hurstolds

Geezer
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Jan 2, 2006
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Not as much as the same exact engine would be with a good set of headers and a 2.5" or 3" exhaust. With any build, it should be a complimentary parts thing, not a dump it out of the box and bolt it on affair without considering how it will help you achieve your goal. Everything you do must be going toward whatever goal it is you're setting. JMO, I think you're putting the cart before the horse if you're starting out with this question. Your first question should be asked to the guy you see when standing in front of the mirror- What's the end goal/dream for this car/engine? If you want to keep it low-buck, you still need a goal to work toward. Since most 455's come in at around 300-ish HP stock already, depending on application, it's not unreasonable to think you could push 350 HP, or even a bit more, real easy out the stock exhaust system.

Always consider this when building an engine for HP- Breathe in, breathe out. If you can't breathe out (exhaust) very well, you certainly aren't going to breathe in (intake) worth a flip either. So if you're going to stay with stock exhaust, you're wasting time and $$ building it to breathe in better with big heads/big cam/tall intake, etc., as you're engine is only as good as the air it can pump through itself. AKA Volumetric Efficiency.

Imagine the idea of the potato in the tailpipe prank. If you restrict the exhaust enough, your engine won't make much power let alone continue to run being constipated no matter how much power it made on the dyno.

If you're contemplating a 455 in a G-body, a stock or mild build with the "stock exhaust" is perfectly fine for the street and occasional drag racing. Do some street bowl work on some stock C (preferred), E, or G big valve heads (even J heads would work if that's all you got, but not preferred), 10.5 compression if possible, dual-plane intake and a performance-tuned quadrajet will make the car completely streetable with some tire-shredding torque on tap to have as much fun as you like. Ensure to use a strong enough transmission with a good stall converter (2500 should be fine behind a 455 as it would act more like a 3000 stall) and driveline to take that extra torque, like an 8.5 from a GN/442. A 7.5" rear would work, but 8.5 would be better. Maybe some new, stronger axles in either can't hurt. You can find out driveline limitations real fast with a torquey 455.

If you buy a 600 CFM E-brock AFB carb for this, I'll disown you. I could see even a Holley spreadbore- maybe, but for one, most of those cheaper AFBs aren't large enough CFM (they do have 750 and 800s that would be better, but their list price is close to $600- likely more than a good Q-jet rebuild will run you), and two, will usually end up running like crap overall on your 455.

These are just some ideas of what ~I~ might do if I were going to build a street 455 with stock exhaust for a G-body. I personally would want to make it look like it came stock that way as much as possible. With 800 cfm VIN 9 CCC carbs, I'm sure I'd even be able to work the ECM into the equation if I got the primary carb modifications figured out for a 455. The secondaries are almost good to go for a 455 as they are.

At any rate, you can find a million opinions on how others would spend your money for you.
 
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Reactions: 1 user
Oct 14, 2008
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Melville,Saskatchewan
Yeah, 2" is small for a 455. The factory was 2.25" head pipes and 2" tail pipes. Even that added 20 HP and similar torque over Olds single crossover POS setup. Also use the BBO specific manifolds as the regular log manifolds suck, they certainly don't blow. A 800 cfm Qjet custom tuned is a good choice, without a doubt.
 
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scarborough

Master Mechanic
Sep 30, 2016
311
66
28
Not as much as the same exact engine would be with a good set of headers and a 2.5" or 3" exhaust. With any build, it should be a complimentary parts thing, not a dump it out of the box and bolt it on affair without considering how it will help you achieve your goal. Everything you do must be going toward whatever goal it is you're setting. JMO, I think you're putting the cart before the horse if you're starting out with this question. Your first question should be asked to the guy you see when standing in front of the mirror- What's the end goal/dream for this car/engine? If you want to keep it low-buck, you still need a goal to work toward. Since most 455's come in at around 300-ish HP stock already, depending on application, it's not unreasonable to think you could push 350 HP, or even a bit more, real easy out the stock exhaust system.

Always consider this when building an engine for HP- Breathe in, breathe out. If you can't breathe out (exhaust) very well, you certainly aren't going to breathe in (intake) worth a flip either. So if you're going to stay with stock exhaust, you're wasting time and $$ building it to breathe in better with big heads/big cam/tall intake, etc., as you're engine is only as good as the air it can pump through itself. AKA Volumetric Efficiency.

Imagine the idea of the potato in the tailpipe prank. If you restrict the exhaust enough, your engine won't make much power let alone continue to run being constipated no matter how much power it made on the dyno.

If you're contemplating a 455 in a G-body, a stock or mild build with the "stock exhaust" is perfectly fine for the street and occasional drag racing. Do some street bowl work on some stock C (preferred), E, or G big valve heads (even J heads would work if that's all you got, but not preferred), 10.5 compression if possible, dual-plane intake and a performance-tuned quadrajet will make the car completely streetable with some tire-shredding torque on tap to have as much fun as you like. Ensure to use a strong enough transmission with a good stall converter (2500 should be fine behind a 455 as it would act more like a 3000 stall) and driveline to take that extra torque, like an 8.5 from a GN/442. A 7.5" rear would work, but 8.5 would be better. Maybe some new, stronger axles in either can't hurt. You can find out driveline limitations real fast with a torquey 455.

If you buy a 600 CFM E-brock AFB carb for this, I'll disown you. I could see even a Holley spreadbore- maybe, but for one, most of those cheaper AFBs aren't large enough CFM (they do have 750 and 800s that would be better, but their list price is close to $600- likely more than a good Q-jet rebuild will run you), and two, will usually end up running like crap overall on your 455.

These are just some ideas of what ~I~ might do if I were going to build a street 455 with stock exhaust for a G-body. I personally would want to make it look like it came stock that way as much as possible. With 800 cfm VIN 9 CCC carbs, I'm sure I'd even be able to work the ECM into the equation if I got the primary carb modifications figured out for a 455. The secondaries are almost good to go for a 455 as they are.

At any rate, you can find a million opinions on how others would spend your money for you.
Thanks for the feed back. the car is a daily driver no track time. its in a 87 Olds cutlass, the engine has been rebuilt 30 over e heads 3 angle valve job new stock piston Edelbrock hyd cam,750 carb. for now I'm thinking of installing a set of Thorton w/z exhaust manifold, an in the future maybe up grading to a set of Edelbrock alum heads.
A set of header for this car is really expensive, and i don't like the style that rap around the frame. its just a nice budget build. like you stated the upgrades you make have to make sense.
 

MrSony

Geezer
Nov 15, 2014
6,862
6,824
113
Des Moines, Iowa
The thorton manifolds look very nice. 2.5 dual exhaust is worth the money by far especially for a big block.
 
Oct 14, 2008
8,846
7,818
113
Melville,Saskatchewan
I assume you mean the early, small dish pistons, not the later soup bowl pistons? The W/Z have 2.25" outlets, unless modified. I see Thornton is currently out of stock. Even the Pypes down pipes go from 2.25" at the manifold to 2.5". I had 2.5" exhaust from my Sanderson shorties to under the passenger side, front to back on my 88. It is possible, even without a dual hump crossmember.
 
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