403 build

[gold66]

I have decided to do a mild build up of the 403 in my fierbird, and could use some help choosing the right parts.... I have set of 7a heads and the edelbrock performer intake and cam kit. The build seems pretty well documented, but I have found that oldsmobile parts arent so so easy to come by. For that reason alone I have decided the 403 should come out of the closet and will sport a proper gold paint scheme when it's done! That and I thought the color looked realy cool on the donor engine I bought for the heads. Anyway the questions.....


The brand name 1.6 rockers that I was going to order are back ordered at the two major mail order companies that I use. Is there any reason I can't go with OEM rockers? I am assuming I can get them from the local GM dealer. Or what about something from NAPA or equivalent?

I wasn't sure which head gasket(s) to use and I ordered the rebuild set for a 403. The guy at NAPA said there was only one kit available so I had him get it for me. I then read about some other suppliers. Any concernes going with the stock type gasket? I think it's a fel pro.

I assume I should torqe the heads to the 403 specs not the 350 specs?

Any suggestions are apreciated.

Thanks!

[Olds64]

Welcome to the website. I think your 403 will be an awsome engine when it is done. Make sure you post some pics.

1) There is no reason you have to use aftermarket rocker arms if you are doing a stock rebuild. If you want to replace them then OEM ones would be fine. However, if you want to spend a little bit of money these ones are decent (Oldsguy used them in his 455 rebuild).

http://store.summitracing.com/partde...T&autoview=sku

2) The stock head gasket is fine.

3) Definitely torque the heads to factory specs.

[J-(Chicago)]

I'd advise that you buy some new 403 2" intake valves and have your machinist cut the seats for them to go into the 350 heads.

If you use the stock 7a 350 head and stock gasket I'd estimate your compression in the high 8s.

If you are looking for more compression, Corteco brand gaskets are a little bit thinner I believe, and could bump up the compression a bit more.

Those comp cams rockers are pretty nice as well. Good call Mr landyacht president.

[J-(Chicago)]

The head bolts are probably smaller than those on the 403 and you will have to have those machined out as well

[gold66]

I understood that the compression will be closer to 9.5 to 1, thus it's not really a stock rebuild and the reason I am worried about the stock gaskets and rocker arms.

The roller rocker kit looks really cool, thank for suggesting it.

[Olds64]

Truthfully, I have never heard of the rocker arms as a weak point on Oldsmobile engines. You might want to do some research on those heads. I seem to remember that the 5A heads are the desireable small block heads. I thought the 7A heads were the smogger heads that came stock on the 403.

[captjim]

It's kinda confusing, but the 7a (small, offset "A") heads "J" referred to are from a 72 350. Then there are 7A (large "A") heads which came off a late 307. 5A heads came off an early 307. 403s came with 4A heads. Lots of guys say the 68-69 #5 heads are the best, but the general consensus is that all the older 350 heads (#5 68-69, #6 70, #7 71, and #7a from a 72) are pretty close to each other. They have a 68 cc (or so) chamber compared to the 82 (or so) chamber of the 403.

But, here is another option. The KB pistons were introduced to give the 403 a decent streetable CR (9.5 to 1 or so) using the 4A head. That head already has the large intake valve, but the exhaust side needs a little work. So, you could use the KBs, spend a few $s on the heads, and have a nice engine. If you decide to use the stock replacements, factor in decking the block as they will probably be .040-.050 in the hole. Research and plan your build carefully. Sometimes you only end up spending a little more to get something a lot better.

[J-(Chicago)]

Good idea Jim. However, I'm not sure that he has a pair of 403 heads. I'm not totally clear on this, but I believe he is trying to make one good motor out of 2. One being a 72 350. I'd just build the 350

[gold66]

Sorry for the confusion. The heads are 1972 7a. Acording to 442.com they are 64cc. I found a motor for sale with the heads on it for what seemed reasonable so I am going for it with a little help from George Busch! I am doing my part to stimulate the economy. I want to keep the 403 because it's stock to the car, why not make it a little sleeper...

Anyway, I am not an engine builder, but I can follow chilton manual. In this case it's a mix between the 1972 350 specs and the 1979 403 specs so thats where I am unsure.

I dont know that the rocker arms are weak, just figured I would replace them since everything else from the cam up will be new. I didn't expect oldsmobile performance parts to be so rare.... Maybe everyone is going with that roller rocker set up.

Thanks again, I do apreciate all of the posts.

[78cutlass]

They're not cheap ($518.00 at Summit), but you might consider adding a set of gold Crane Olds roller rockers, 1.6 ratio. Have a reputable machine shop install them properly. Supposedly, they're worth an extra 25 HP or so.

[captjim]

There are many discrepancies on 442.com, don't take any info you read on there as Gospel. You will find those heads closer to 68-70 cc. I would keep not even bother with the 350, just use your 403 and the KB pistons,
http://kb-silvolite.com/performance....tails&P_id=354
do a little work on the heads and be done.

[88 coupe]

Originally Posted by gold66

........ Is there any reason I can't go with OEM rockers? ........

Not as long as you stay under .550" valve lift.. I've been using Pioneer, OEM replacements, with no problems.

Originally Posted by 78cutlass

........ Supposedly, they're worth an extra 25 HP or so.

Not possible. Any gain would be hard to measure accurately.

Good example of how internet myths get started.

Norm

[J-(Chicago)]

Originally Posted by Olds64

Truthfully, I have never heard of the rocker arms as a weak point on Oldsmobile engines.

Stock rockers are pretty tough little pieces. It's the bridges that are pieces of crap. I wouldn't waste my time with those. They break often.

[88 coupe]

Originally Posted by J-(Chicago)

........ They break often.

They don't just "break" by themselves, they get help. The aluminum (OEM) versions do tend to break, if they are installed/uninstalled with the cam in the wrong position.

Not a problem, if it's done when the cylinder is on its compression (both lifters on the heel of the cam) stroke.

Norm

[J-(Chicago)]

Again, Norm is correct.

I only end up breaking them on disassembly, and when I just "tear into it" instead of taking the time to rotate and be gentle.

If I know they're not going to be reused, I don't take as much care with them.

P.S.
Welcome back.

[Warhead]

Make sure to drill the head bolt holes on the 7a heads to 17/32nds, and you will most likely have to drill one of the locator pin holes to the correct size on each head. Please put a 2" valve in the 7a heads, with good oil seals.

Early rockers must be used with early pushrods, later 77 and up stuff has a larger ball end on the pushrod and cup, and their lengths will differ. Either use ALL the early pushrods, and rockers, as a set-- or ALL of the late model pushrods and rockers, as a set. Don't mix em up. They will interchange, but only as a set.

[captjim]

I don't know if it is fact, fiction, or opinion, but several guys including engine builders have told me that adding a larger valve without a little port work is a waste of time and money. That is why I suggested using the 4A heads with some work and the KBs.

[Warhead]

I don't know if it is fact, fiction, or opinion, but several guys including engine builders have told me that adding a larger valve without a little port work is a waste of time and money.

I have no problem with your suggestion of the 4A heads, but I have got a DAMNNED BIG problem with this statement, especially on a 403.

Not true.

The intake valve cutain area is very important on a 403, including the 1 inch leading to the seat. Do not make it smaller with a 1.87 IV from the 350. A lot of people have had success with a 1.87 intake on a 403, but they left an easy 20+ horse power on the table using those heads that way. FACT!

All I wanted to see was he at LEAST kept the factory 403 intake valve size. NOT a lot of work guys.
I know his budget will dictate his actions.