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Old 02-26-2005, 10:30 PM
musclecarlovinchick musclecarlovinchick is offline
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I have a 1979 Trans Am that I am in the process of restoring. Can anyone tell me if the Olds 403 is considered a large or small block? I thought it was a small block but am now hearing that it is a big block. I ordered more parts for it this week and got asked yet again if the 403 was a big or small block. It is frustrating to go to buy parts and have one parts store say one thing and another say something else.

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Old 02-26-2005, 10:30 PM
musclecarlovinchick musclecarlovinchick is offline
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I have a 1979 Trans Am that I am in the process of restoring. Can anyone tell me if the Olds 403 is considered a large or small block? I thought it was a small block but am now hearing that it is a big block. I ordered more parts for it this week and got asked yet again if the 403 was a big or small block. It is frustrating to go to buy parts and have one parts store say one thing and another say something else.

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Old 02-26-2005, 10:42 PM
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The Olds 403 is actually a small block. It has the shorter deck height like the 350. 455 Olds is has a taller deck. A lot of the parts will interchange however. Like heads, intake, headers etc...

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Old 03-01-2005, 08:04 PM
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Thanks for the information! Had to order more parts today so the info came in handy. Thanks again!

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Old 03-03-2005, 03:04 PM
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Hello there - just noticed that you are in Washington - I am in Spokane and have many spare parts from the 403 I swapped out of my 78 T/A - is there anything you need in particular? I even have a newly-bored 403 block and a newly-rebuilt set of Olds 350 heads with higher compression that will bolt right onto the 403 block. You can e-mail me at joebanna@yahoo.com and let me know...

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Old 03-03-2005, 06:44 PM
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I have a friend looking into maybe getting a set of olds heads for his 403. What 350 heads do you have? were they bored to fit the 1/2" head bolts of the 403? What kind of work was done to them? Im not sure if you want to ship them but if you do how much $$ are you looking for them?

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Old 03-03-2005, 09:17 PM
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The heads to use are 330 heads / 350 heads. 1967-1972. Specifically...#4, #5, #6, #7,or 7a (little capital a). All others are junk smog castings 1973 and after are boat anchors. The #4 has the smallest stock combustion chamber size w/o milling. Drill them to 17/32..stick in your 403 valves...done. Now you have 9:1 instead of 7:9:1....

olds

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Old 03-09-2005, 12:20 AM
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hey, you want A LOT more info on your 403? Talk to people who specialize in our motor on realoldspower.com unfortunately the site was recently hacked and the whole database in threads is now gone. But plenty of Olds enthusiasts are there to help answer questions. Check it out, they know how to build up 403's and make serious horsepower, even with the windowed main webs

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Old 03-14-2005, 09:59 PM
musclecarlovinchick musclecarlovinchick is offline
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Thank you! I will check it out.
Michelle

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Old 03-14-2005, 10:46 PM
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musclecarlovinchick,
I would recommend replacing the 403 with an Olds 455. Here is an article written in the Trans Am Club Newsletters several years ago. Hope you find this helpful.

Second generation T/A and Formula’s owners with the 403cid Oldsmobile motor have an abundance of factory Oldsmobile parts available to transform their cars into high performance vehicles capable of “blowing the doors off” of a Pontiac (please don’t give me a hard time for saying that…remember the 442, Hurst/Olds, W-30, W-31 cars were pretty quick). Swapping out the Olds 403 motor with an Olds 455 is the best way to go, preferably if you are fortunate enough to get your hands on some W-30 engine pieces for the Olds 455. The Olds 455 produces a lot of torque (Bore x Stroke = 4.126 x 4.250).

If you have thought about this conversion, first you will need to seek out an Olds 455 block. These engines were produced from 1968 to 1976 and can be found in Oldsmobile 98’s, Toronado’s, Custom Cruiser Wagon’s and certain 442’s and Delta 88 models. Your best probability to find a complete running Olds 455 engine is to purchase a ‘68 thru ’76 Olds 98. If you look hard enough, these cars are still running around and can be picked up for a low price.

There are several quick ways to identify a ’68 thru ‘76 Olds big block versus a small block. First, ’68-’69 455’s were painted red, ‘70-’76 455’s were painted blue versus the Olds 350’s of the same time period were painted gold (except in ’75–’76 the 350’s were also painted blue). Through appearance, an Olds 455 looks wider than an Olds 350. Also if the cylinder head is still on the engine, all 455’s had a large letter (C,D,E, F,G, H or J) cast onto the cylinder head located by the outer exhaust port. An Old 350 will have a number cast onto the head in the same area. Below is a guide to get started in your search for the right Oldsmobile parts.

ENGINE BLOCKS
The casting number (and letter) is located on the front of the engine block, visible externally between the intake manifold and timing cover.

YEAR(S) ENGINE SIZE CASTING #
68-72 455 396021 F
72-76 455 396021 F A

CYLINDER HEADS
The casting letter is located on the corner pad next to the outer exhaust port. On the left cylinder head, the letter will be located towards the front. On the right cylinder head, the letter will be located towards the back corner.

YEAR CASTING PART APPLICATION
68-69 C 394548 All 455
68-69 D 400370 W-30, Hurst/Olds
1970 E 403686 455 except W-30
1970 F 404438 455 W-30
1971 G 409100 455 except 4-30
1971 H 409160 455 W-30
1972 GA 409100 All 455
73-76 J 411783 All 455
K Marine Applications

The most widely produced head will be the “C” casting head. Many of these heads were produced during the late ‘60’s. However, there are two versions of the “C” head. The big valve head (2.072 intake) was used on 4bbl cars and the small valve head (1.998 intake) was used on 2bbl cars. All use 1.625 exhaust. Avoid the small valve heads. “D”, “F”, “H” and “K” heads (W-30 series) feature improved port configuration for better flow. These heads were produced in low quantities, but are the most desirable.

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Old 03-14-2005, 11:37 PM
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An olds 455 is cool, but the 403 can be built well also for street applications. Especially if you are restoring a numbers matching car, not to mention the T/A shaker scoop will not fit right with the taller deck of the 455 block. A well respected olds 403 builder is Terry Fritsch at FCR Performance. He can help you build a strong 403 and tell you exactly what you need to order, he is very helpful and knowledgable with olds motors. here is his website link: http://www.fcrperformance.com/

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Everything installed, fired up and tuning has begun!
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Old 03-15-2005, 06:09 AM
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Not knocking the 455olds..but a well built 403 will give a 455 a run for its money. There are a lot of parts for the 403 that did not exist 2ys ago.

By the way. FCR did my heads on my motor and custom ground a cam for me. Take a look at the April 2005 Popular HotRodding Article on the 600HP 403. J&S engines posted part of it. Jim at J&S has some pics of several 403's.
http://www.jsmachineoldsmobile.com/

olds

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Old 03-15-2005, 07:47 PM
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and are 60+ pounds lighter...

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Old 03-15-2005, 09:19 PM
musclecarlovinchick musclecarlovinchick is offline
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Thanks for all the information. At this point, I am planning on keeping the car all original. If I dig into the car and find numbers that don't match (as the previous owner assured me they did match), the motor will be eventually swapped out. I am finding the restoration to be a huge project! Thanks again for the great information!
Michelle

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Old 10-14-2020, 10:45 PM
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Default Upgrading to 68 - 72 Olds 350 Rocket heads - need help.

I ran across this thread and decided to post here rather than start a new one and the write up that GTO4DOOR did here was fantastic - great info.

I recently purchased a 79 Trans Am with a 403 Olds that was mildly built by the previous owner - mainly cam and intake I think. He could give me no information on the engine other than that.
Shortly after purchasing, I blew the head gasket. As long as I need to have the heads checked, I want to build the compression by adding 1968 - 72 Oldsmobile 350 #5 heads or similar.
I need help in locating a set that are useable and what they should cost me.
I know I have to enlarge the head bolt holes, drill additional coolant passage holes and use the valves from my stock 4A heads in the 350 heads.

I will shelf the 4A heads as they are the originals to the original 403 engine.

The current heads (valves) look good and I also acquired 2 intake and 2 exhaust valves still in the box new.
I am a mechanical guy but I have not personally done any head work. What do I need to do to put in the larger valves?
Can I use all the same push rods and head components swapped to the different heads.
If I do the bolt hole and coolant passage modification What might it cost to have a shop do the work to just make the heads bolt on and go?

I found this info on the Olds heads
https://oldsjunction.classicoldsmobi...sfaq/ofhed.htm

Also below are some pics - not sure what I have here as far as stock equivalent. I am a GTO guy so I only have the experience of driving some of these TAs for possible purchase. Most of them were dogs - this one runs strong. Somebody did some nice work as it runs much stronger than stock.

Looking for advice

Thanks guys
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Old 10-15-2020, 02:32 PM
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I will offer a counter-argument - I feel the 403 is superior to the 455. The 455, being much taller, has a very compromised intake manifold design, which limits power at upper rpm. Unless a person is willing to forgo the shaker scoop, and install some sort of cowl induction hood, the 455 just is not going to fit with a decent intake manifold on it.

I've also gong through the trouble of installing older heads (off of a 330) onto a 403. The older heads have smaller valves than the 403, and (although I've need seen flow bench data) are likely to have less flow. You gain a teensy bit of compression ratio, but give up CFM - NOT a good trade IMHO. Just mill the 403 heads, or use pistons that will raise the CR. I've helped with a couple of 13 second 403 motors, and had another friend who got his 403 daily driver into the 12's with just 3.42 gears. All were very reliable performers.

There is some guy on eBay selling aluminum heads for 403's. I have not tried those, but they look to be worth considering - they will give you both better CR AND more CFM, and that will give you more power.

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  #17  
Old 10-25-2020, 03:14 PM
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Thank you Lee for your comments and your advice on the 403. I am just trying to add compression or performance by bolting on heads, as the engine is in the car and I am repairing a blown head gasket.
The short block checks out okay and I wanted to add performance as easily as possible. The car has gears that are above 3.25 but below 3.50 and performs okay with the stock 403 heads. I have been advised by adding 350 heads with bigger valves will flow better and bring up the compression by 1 - 1.5 points.

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Old 11-06-2020, 09:59 PM
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To the guy that reignited this thread and to you too, Lee, I am glad to see some folks using the 403 instead of dumping it for something else. Granted it has its limitations and will not tolerate the power levels of the Pontiac 400 but with the right combination of parts it can be a very good performer. I retained the 4A heads and went with the KB hypers to get the c.r. up to 9.4. This included zero decking the block and facing the heads but not taking off so much as to require that my RPM manifold had to be cut. Valves were opened up to 2.00/1.62. I did my own head porting with instruction from a guy who knows his stuff. Overbore is .024 and I did beef up the mains with the main cap supports that Dick Miller sells. Cam is nothing radical, an old Ultra Dyne flat tappet at 226/233. Car idles at 850 and is pretty quite through the full exhaust and Super Turbo mufflers. Car runs consistently in the 12.10 to 12.20 range and has gone 12.01 in really good air. Hope you guys can make the 403 work for you because it is a very under rated engine, and will surprise a lot of folks.

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Old 11-06-2020, 10:10 PM
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It'll handle similar power to the late 400 which is still plenty for the street. Unless you have big HP requirements or plans for boost-adders, there's no reason to go hunting for something else. What's worse is where they follow bad advice online and source another block or engine, and then only modify it to levels that weren't an issue for the original block, 400 or 403 or anything similar of the era.

My 403 has a very mild build just shy of 400hp which is still plenty when you consider the torque these produce. That's not too bad for something that appears stock, including original low intake, heads, carb and exhaust manifolds (Thorntons). That was something I wanted retained. It should make for a nice grunty, low-RPM cruiser with the 200-4R when complete. Actually, the specs are similar to above minus the RPM intake and a tweaked cam with more open valve time.


Last edited by Aus78Formula; 11-06-2020 at 10:16 PM.
  #20  
Old 11-15-2020, 02:02 AM
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Thanks for the input gentlemen,
As I said earlier, I am not familiar with the 403 upgrade options and I want to bring up the compression ratio from stock 1-1.5 points and I have found two pair of small block heads locally
1st pr is cast# 409147 7a's from 1972
2nd pr are cast#409147 7 from 1971
I believe they are both 64 CC heads.

Am I better off using the stock 4A heads or using one of the sets I found locally. Which set would be the best and what would I need to instruct the machine shop to do to the small block heads to make them a bolt on option for me?
I know the bolt holes need to be enlarged to 1/2" and I believe additional coolant passages need to be drilled. I read that the valves from the stock 4As should be used in the small block heads.
What am I missing?

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