Ashtray77

Engine gurus, recommend me some parts!

I have some ideas on what I'd like to accomplish with a future engine build for my TA, but not sure which parts would work best together. I have a '79 Pontiac Trans Am with factory Oldsmobile 403. I originally thought about swapping in a Pontiac engine, either a 400 or 455, but I thought, why not do something with the engine that's in it?

Current specs of car:

Stock 403 at around 185 horsepower (assumed, although I just had true dual exhaust with "X" put on it 2.5" diameter so it might be more), stock exhaust manifolds with crossover hole blocked off (don't want to mess with headers), TH350 transmission which I'll probably keep, and 2.41 geared rear that will be switched out for either a GM 10 bolt, or Ford 9 inch, something in the 3.08 to 3.23 range. Subframe connectors are getting installed in a couple of weeks. Haven't decided if I'm keeping the stock wheels, and thus brake size.

Here are my hopes:

1. Dependable. I fully expect to use a main girdle from J&S and all new bolts.
2. It has to fit back in the car without modifying the shaker hood scoop. Stock intake height needed. Edelbrock 3711?
3. Fun, but not "too" fun. It's a street build. Decent mileage (for a muscle car) and street manners but, 400 horsepower sounds nice, and 1/4 mile times in the low to mid 13's on radial tires would be fantastic.
4. Run on pump gas. Would prefer to use 87 octane, but could use 91. That is about as high as is available around my neighborhood.
5. Somewhat frugal. I don't have a set budget that would limit me to reuse parts or cut corners that might cause concern (see #1), but it's nice to save money if you can.

Well, that's all I can think of right now. Let me know what you all think.

Thanks in advance!

-Aaron

Olds64

Aaron, why do you want to install a girdle when you rebuild the engine? Even with the windowed mains an Olds 403 isn't going to have bottom end trouble with a mild street/strip build.

I suggest you install good pistons when you rebuild the engine and swap to better small block heads. It's good that you plan on changing the rear gears, but why swap to a Ford 9" when there are aftermarket gears and kits for the differential you already have? Also, consider doing a mild upgrade to your transmission. A stall converter and a shift kit can work wonders. Good luck!

olds 307 and 403

Problem is only cheap cast pistons work with early heads. Use KB hyper 6cc hyper pistons or Arias forged to bump your compression. You could use #8 heads, which are a better start and still have a 77-78cc chamber for those pistons. Your 4A aren't bad on the intake side, open the bowl and add a 2.07" intake valve. The exhaust needs a 1.625" valve with the bowl opened up and a ton of port work, pretty awful. The Performer is lighter and similar in height to your stock iron intake. Cutlassefi could do a custom cam to help with your 4A heads.

Ashtray77

I've read everywhere that the windowed mains were a big weakness of this engine. J&S Machine's stage 1 girdle is listed for up to 325 horsepower, and since I want more than that, I assumed that I would need at least a stage 2.

From what I've read, the 2.41 gears that I currently have use a different carrier than the gears that I want. I've seen that there are kits that require the use of a spacer that would allow 3.08-3.23 gears in this rear, but from what I remember researching this from over a year ago, it is the prevailing opinion on internet forums that I'd be better off swapping the whole rear to a 10 bolt that already has that carrier. As far as the Ford 9" goes, they are supposed to be bulletproof, and there is a fairly well respected shop in my area that does conversions. This particular shop's opinion is that after going through a 10 bolt, making it good to go, it wouldn't be much cheaper than going with the 9".

Ashtray77

I was leaning towards KB hyper pistons. My only concern is that bumping up the compression too much with iron heads would not allow me to use 87-91 octane pump gas. I don't know where the compression limit lies for this. From what I understand, aluminum heads are a little more forgiving.

Thanks for the input!

joe_padavano

People loose way more sleep over this than they should, and speaking as an aerospace engineer specializing in structural design, I can tell you that most girdles on the market are worthless. Unless the girdle is tightly fitted with press-fit pins, it isn't doing squat. The main caps are much stiffer than any girdle I've seen, with the result that the slop in the fastener holes doesn't allow the girdle to carry any significant load. Like TSA, girdles provide the appearance of security.

Richmond sells thick gear sets for your 2-series carrier that don't require spacers.

Ashtray77

Interesting points on the girdle, this is the first I've read this. Also, I wasn't aware of the 2-series specific gear kits. How much power can a 7.5" rear handle though?

In my opinion, I'd rather be over, rather than under-engineered.

Thanks for the info!

joe_padavano

7.5? I thought your car has an 8.5 axle.

Olds64

Oh! Nuh-uh he didn't!

Really though, you mentioned you wanted a "street build." We're here to tell you that there is no reason to run a girdle on a 403 for a "street build."

joe_padavano

This probably means I'll get pulled out for the "special" screening next time I fly...

Ashtray77

To be honest, I'm not exactly sure what it is. I should probably verify that before I make myself look stupider. I admit, all I know about this stuff is what I've gathered online. All the places I've looked, I haven't seen any gear sets that are for 2-series carrier for a 8.5" rear.

Thanks,

Aaron

joe_padavano

My apologies. Despite typing "8.5" into Google, it sent me a link for thick gears for a 7.5 axle, and I didn't notice that at first. Richmond does not list thick gears for an 8.5. Frankly, 8.5 differentials aren't that expensive.

Fun71

I agree, an 8.5" posi carrier plus a new gear set would not be anywhere near the cost of a Ford 9" set up for a Trans Am.

Ashtray77

O.k., I think I'm starting to understand. from what I'm gathering, I most likely have a 8.5", not a 7.5", and I would need to change out the carrier along with the gears.

So, now that we have that settled, any more thoughts or tips on the engine?

Fun71

Just reread your first post and for #2 maybe consider the 2711 intake manifold if you are not going to retain the EGR system.

That's all I have.

Ashtray77

That is something I hadn't considered. From what I'm reading, it seems that it would be a benefit to keep EGR.

Olds64

EGR is an emissions control device. If you get rid of it you may have to be wary if your state requires safety/emissions inspections. Deleting it in certain states would surely make a car fail inspection.

If you remove it you might get a marginal boost in HP. Non-detectable by the butt dyno for sure. If you delete it you should also re-curve your distributor since "smog" era distributors are curved for emissions.

VC455

Engines with EGR recirculate exhaust into the intake to lower the flame temperature and produce lower NOx.

The flame temperature is lower because there is not as much oxygen in the combustion chamber--exhaust gas displaces oxygen. Oxygen is what burns gas and makes power. The more oxygen you have, the more gas you can burn, the more power you can make.

Its the same principle behind turbos and superchargers--they cram more oxygen into the cylinder.

The only advantage I can think of in keeping EGR is that you will likely not need to rejet your carburetor. If you eliminate EGR you will need to have your carb reworked by an expert to get maximum power. That's not a big expense in terms of your total budget and is essential to reaching your HP goals without resorting to an overly big cam.

joe_padavano

This is correct, but EGR should only be functional at part throttle cruise under light loads. Unless the EGR valve is stuck open, there is no impact to W.O.T. performance.

Ashtray77

Good info guys. Iowa doesn't have emissions testing requirements, so I don't have to worry about that. That said, if I find a deal on the 3711, it looks like I can delete the EGR with a block off plate.