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Old 11-24-2012, 02:08 PM
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403 SBO 4a heads

Hi, im in the progress of buying a 1979 Trans AM and have researched a lot on how to improve performance from the measly 185hp it put out. I've been told to put early heads (68-72) on it mainly 1972 #7a heads from a 350 were the best but i really cant find any anywhere i was wondering if there was there any possible way to get good performance (350-400hp) out of the #4a heads that came stock with the 403.

Thanks For any input,

Trey
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Old 11-24-2012, 03:47 PM
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Originally Posted by 1979 TA View Post
Hi, im in the progress of buying a 1979 Trans AM and have researched a lot on how to improve performance from the measly 185hp it put out. I've been told to put early heads (68-72) on it mainly 1972 #7a heads from a 350 were the best but i really cant find any anywhere i was wondering if there was there any possible way to get good performance (350-400hp) out of the #4a heads that came stock with the 403.

Thanks For any input,

Trey
The whole reason for swapping heads is to get the smaller chambers and raise the compression. The 4A heads have something like 80 cc chambers, same as a BBO. The earlier heads have 60-64 CC chambers. The problem is that the early heads also have smaller valves than your 4A heads, so you need to have them cut for the larger BBO-sized valves (Olds did this for the W-31 motors). I'm not sure where you are looking, but #4, 5, 6, 7, and 7a (not to be confused with the 7A heads on the 307s) are pretty easy to find. Cores should run in the $100/pair range.

As far as your 4A heads, the only thing you can do to increase CR is to change to flattop pistons, not an inexpensive solution. If you're looking for the best performance upgrade to a 403, get BBO heads (Cs are good, but all except Js are comparable), flattops, and a Performer RPM ported to match. The C heads worked great on a BBO 400, they'll work equally well on an SBO 403.
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Old 11-24-2012, 04:02 PM
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looks like I should go with the 1972 350 7a heads then since it seems to be the cheapest option. Were those heads only on the 1972 cutlass? and do you think a junkyard might have them. If i do use them then i wouldn't have to change the pistons?
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Old 11-24-2012, 04:21 PM
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Originally Posted by 1979 TA View Post
looks like I should go with the 1972 350 7a heads then since it seems to be the cheapest option. Were those heads only on the 1972 cutlass? and do you think a junkyard might have them. If i do use them then i wouldn't have to change the pistons?
#4 was 1967
#5 was 68-69
#6 was 70
#7 was 71
#7a was 72

The same heads were used on all SBOs (A-body and full size) in a given year, and except for the W-31s all had the same valve sizes. The 7 and 7a heads have hardened seats, but these are simply induction hardening of the parent cast iron, not separate press in seats. If you cut the seats for big valves (or even have too many valve jobs done) the hardened area is machined away. If you do elect to have hardened seats installed, be sure the machine shop uses Olds-specific seats. The common Chevy seats are too tall and the shop will hit water if they cut the heads too deep.
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Old 11-24-2012, 04:30 PM
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Thanks man that's some great information I didnt know the hardened valve seats could be machined away also didnt know you could install them either. so any of those heads should bump it up to about a 9.5 with the right gasket and spacing?
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Old 11-24-2012, 06:34 PM
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Sure you couldnt get an LT1 or LT4 for the same money. Even a good first gen sbc. The olds motor is junk and will never make big power, just suck up cash and never make you happy. A chevy motor would be very cheap and make more power than the olds for alot less money probably enough to offset the price of the swap and chevy style trans.

Any pontiac engine will bolt in without changing the trans but if it needs to be built chevy may still come in cheaper.
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Old 11-24-2012, 07:15 PM
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Sure you couldnt get an LT1 or LT4 for the same money. Even a good first gen sbc. The olds motor is junk and will never make big power, just suck up cash and never make you happy. A chevy motor would be very cheap and make more power than the olds for alot less money probably enough to offset the price of the swap and chevy style trans.

Any pontiac engine will bolt in without changing the trans but if it needs to be built chevy may still come in cheaper.
LMAO!

Obviously this guy doesn't know **** from shinola when it comes to engines. the 403 Olds or even a 350 Olds can make more than enough power to make your car a blast to drive.
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Old 11-24-2012, 07:48 PM
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LMAO!

Obviously this guy doesn't know **** from shinola when it comes to engines. the 403 Olds or even a 350 Olds can make more than enough power to make your car a blast to drive.

I know ive read enough on the 403 to know that it can be a kick ***** motor and that the windowed main webs shouldnt scare me
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Old 11-24-2012, 08:52 PM
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Yes you can get power out of any engine with careful tuning. But at some point in the cars life that olds motor is coming out of the car if you keep it long enough. Sometimes its cheaper to build something sweet all at once than to mess with something put together out of rare or old parts.

Seen the olds route run a few times most ppl dont end up happy with the cost and results. Maybe one but not both.

Rasing the compression ratio that much if it doesnt knock its going to make some power with a good cam. So olds will give you some kick dont get me wrong.
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Old 11-24-2012, 09:42 PM
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Originally Posted by hcompton View Post
The olds motor is junk and will never make big power, just suck up cash and never make you happy. A chevy motor would be very cheap and make more power than the olds for alot less money probably enough to offset the price of the swap and chevy style trans.

Any pontiac engine will bolt in without changing the trans but if it needs to be built chevy may still come in cheaper.
The MAIN thing "wrong" w/Olds power is dumbasses who:

1. do not know jack about them (same thing w/Q-jet carbs), and...
2. people who try to build them like a Chevy (same thing w/Pontiac engines).

An Olds engine can perform just fine. Even the 403- as long as the expectations are realistic. They'll run w/most anything w/a ~5500 rpm redline.

But the LAST thing the hotrodding world needs is another Pontiac w/a Chevy engine in it- even if the factory wimped out and did it, too (and a 305 at that).

Last edited by cobalt327; 11-24-2012 at 09:55 PM.
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Old 11-24-2012, 10:41 PM
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Originally Posted by cobalt327 View Post
The MAIN thing "wrong" w/Olds power is dumbasses who:

1. do not know jack about them (same thing w/Q-jet carbs), and...
2. people who try to build them like a Chevy (same thing w/Pontiac engines).

An Olds engine can perform just fine. Even the 403- as long as the expectations are realistic. They'll run w/most anything w/a ~5500 rpm redline.

But the LAST thing the hotrodding world needs is another Pontiac w/a Chevy engine in it- even if the factory wimped out and did it, too (and a 305 at that).
Amen to that
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Old 11-25-2012, 07:55 AM
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The MAIN thing "wrong" w/Olds power is dumbasses who:

1. do not know jack about them (same thing w/Q-jet carbs), and...
2. people who try to build them like a Chevy (same thing w/Pontiac engines).

An Olds engine can perform just fine. Even the 403- as long as the expectations are realistic. They'll run w/most anything w/a ~5500 rpm redline.

But the LAST thing the hotrodding world needs is another Pontiac w/a Chevy engine in it- even if the factory wimped out and did it, too (and a 305 at that).
You can build an Olds just like any other engine, chevy, chrysler, ford, fiat, etc it DOES NOT MATTER what brand it is. Its just a big ol chuck of iron.

Get some 7a heads, add the larger valves, and port them out (these heads can flow a LOT for stock small block heads when done right), get in the 9.5:1-10:1 compression range, a good set of headers, a cam close to this one Street Strip Solid Cam - Oldsmobile V8 276/284 - Lunati Power , an RPM intake, a 800cfm or larger carb, and if you can freshen up the short block and add new bolts and a good balance job.

An easy 450+hp combo.
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Old 11-25-2012, 08:48 AM
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Originally Posted by cobalt327 View Post
The MAIN thing "wrong" w/Olds power is dumbasses who:

1. do not know jack about them (same thing w/Q-jet carbs), and...
2. people who try to build them like a Chevy (same thing w/Pontiac engines).

An Olds engine can perform just fine. Even the 403- as long as the expectations are realistic. They'll run w/most anything w/a ~5500 rpm redline.

But the LAST thing the hotrodding world needs is another Pontiac w/a Chevy engine in it- even if the factory wimped out and did it, too (and a 305 at that).
Its a pontiac and it does not have a pontiac engine in it. Olds chevy are no different to the hotrodding world. Either way you look at it they dont belong there. Buy a 4 speed car with the poncho 400 in it.

Those engines were put into the car cause they were cheaper to build and got better milage. They never made any power. Sorry you think you are going to swap heads and go from 185 hp to 400. That is not even possible no matter how you look at it. You are suggesting that a head swap will make an olds 403 into a tq monster like the poncho or chevy 400 and you know that is not true.

Your going to swap heads cam intake carb full exhuast, ingnition and fuel upgrqdes. And when it hits the dyno it will make 240hp. You will be running 14 second 1/4 and the guy with the chevy or poncho engine will be in the 11's or 12's with less out of pocket cash spent. I have never seen anyone pop the hood on a t/a and go great its still got its original 403.

I have a friend that had a turbo trans am with the turbo engine removed and an lt4 installed with a 6 speed it got 24 mpg on the highway and pulled the front tires off the ground at the race track. And this was 15 years ago the engines and trans are way cheaper these days. He got a good deal on the engine and had been racing the car for years when he put his full on race motor into a vega and put the ta back on the road. He did change the cam and fixed all the flow issues with the intake and had a good exhuast system built. But he had the stock lt engine in the car i drove it around it moved. Even without the upgrades.

I am just trying to suggest that the 403 may end up eating cash and not giving you what you paid for. Poncho engine would atleast be fast once you put a ton of money into it. Most t/a need so much body work putting to much money into the engine can kill the project as you will spend too much and not have the cash to fix the car.

I would make the car perfect then put any new engine into it. Your car will be worth a lot more cash if the body paint and interior are in perfect condition i would try to avoid building it engine first. Best thing bout the 79 auto is it does not effect the vaule to change the engine. Most ppl will be happy to see one with a better engine. Pontiac 455 sd or ho is preferred but chevy is still a very valuable option in these cars. Becasue they are great drivers and ppl love to take them to work and cruise every weekend.
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Old 11-25-2012, 12:17 PM
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You are just too wrong in too many areas for me to waste my time on- I'd be here all day.

1979 TA- PLEASE use your best judgement. Listen to people who have actually done these things and not just read a mag or googled it.

Member joe_padavano knows as much about the Olds as anyone on this board, I would recommend you listen to him (I have only built two Olds engines from the ground up, a 350 and a 455).
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Old 11-25-2012, 12:57 PM
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AFA making power from stock, the 403 olds is no different from building a 400 sbc, except that it has windowed mains and so you need to keep the rpms below 6k if you have plans to abuse it. It has a huge bore and with the right heads (the bbo heads will put you ahead of the sbo in everything except static compression) it will make great power. He's not building an all out dragster and with careful consideration to how much he spends on his top end he could easily build an engine that will outpower anything chevy that displaces 5.7L (gen or gen II) at a similar cost. It's not hard, just takes careful thought and patience.

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