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Northstar Camaro Club Forum » Technical » Engine Tech » 403 Olds
Does anyone in here have any experience with the Oldsmobile 403 small block? I’m wondering how they respond to mods and what type of work it would take to get about 350-400 hp to the wheels (through a TH400, if it makes any difference).
Also, if you bore the 403 to a 411, what power output differences would you see with the larger displacement? I've never seen any dyno sheets or anything of a "before and after" from boring, so I am curious as to how much of a difference it makes; not only with 403s, but any engine at that.
Can't address the first question. I don't know if there is much out there for performance parts.
Just increasing the displacement that little with all other factors the same; piston configuration and compression, same cam, fuel, exhaust, the power increase would be negligible. Maybe 1-2 hp per cylinder...
Well the vehicle is a 79 Trans Am. There would be no forced induction in the future; just bolt ons. The vehicle is my uncles, and he has owned for a good 20 years or so. The motor has been fully rebuilt (not sure of the specs, but I'm pretty sure its not a stock rebuild) and the trans is a fresh TH400, so it would more than likely keep the 403. He believes the motor puts out between 350-375 hp, but it has never been on a dyno. I guess the logical thing to do would be ask him what is done to the motor, and then come back with the information to see what else could be done. I know there are larger headers, true custom duals, Holley double pumper, etc...but let me check on the motor specs and then I'll post them up in here.
Thank you for the input though.
Pushing it for a 403 if he has a cam and heads supporting 375hp. If it is important to keep the numbers matching, I would pull the engine and store it. Then I would seriously think about switching over to another pontiac, or even a full chevrolet driveline for playing and store the original hardware on the chance that 79's become high in demand. Not trying to be harsh here, but the 403 is absolutley not a performance block. I wouldn't put much work into it if I didn't have to. If you want something hot, look into another BOP platform. Most will drop right in. Which heads, what was done, cam specs and the pistons used will help everyone figure out whats what, but if you want 400hp, there are cheaper and easier ways to get there. Have you thought about a olds 350 or 455?
I am not too worried about keeping it numbers matching. My main reasoning on keeping the driveline the way it is, is simply because the motor has only a few thousand miles on it, and the tranny less than a hundred. Mechanically, everything is fine; the only issue that would resort to a swap is that its not pushing out the numbers I would like it to. I have been reading up on 455 swaps, as they seem to be pretty popular from what I'm understanding. We are not looking to make it into a drag queen however, so that brings us right back to the "Dyno it, get your numbers, and be happy with it" approach.
I'm looking for big numbers for bragging rights (I mean, come on, who doesn't like to say their car puts 400 to the ground? lol), but as I stated before, it would not see a drag strip too often, and would not be raced on the streets. Straight line performance would be the priority however. Sounds is good (true aftermarket duals) and idle is good. The overall goal would be a reliable, safe, and sharp looking vehicle, that when taken to the track on rare occasions wouldn't be put to shame by, say, a stock LT1/LS1/4.6L/5.0/etc. Definately not looking to run head to head with vipers, but enough to hold its own against others within the 300-400 range at the track.
I talked to my uncle briefly today as well. The heads are 403 olds heads with "some work" done to them, and it has a "big cam-not stock at all." I'll have to find out what the specifics are when he has more time to sit down and talk.
Where are some places with dynos in the Eastern MN/Western WI area? The only one I know of is where Dyno Days was held...
There are a number of others such as Wheeler in Blaine and TPIS in the Shakopee area but St.Paul Automotive is one of the closest to you.
Alright, I was thinking I would take it there anyways, because of how good they were during Dyno Days. Gotta support the ones who support the club:)
Well, turns out I bought the trans am. So its now legally mine. Which brings up some further curiosity and ideas of what I should do with it. What I know so far is that it's a 403 bored to a 411, with roughly 5k on it. Aftermarket intake, headers, carb, exhaust, and AC delete. Fresh TH400 with less than 100 miles. Not sure of mileage on body, but if I remember correctly it was around 50-60k. I plan on taking it out of storage as soon as the streets clear up here, probably in about a month or so, depending on the weather. The first thing I will do it get it on a dyno. If I'm lucky, hopefully Ill have 300+ HP and 400+ tq. But I suppose it could be as low as 230hp and 350 tq. I'm really not sure. Because of the low-mileage drive train, I won't be replacing any of that anytime soon, if at all. I've been reading up some more on the Olds 403s, and I have came across both good and bad things. Does anyone in here have anything good they know about the 403? Cause it seems like the bad things are outweighing the good right now. Especially overheating issues and low compression. I will probably have to address the overheating with a good radiator, low thermostat, and just keep an eye on the engine temp. The reworked heads on the 411 will hopefully help the compression a little, but I'm not too tech-oriented to know much about that.
I'll keep you all updated when I learn more specifics.
Also, I'll add, a large deciding factor in whether or not to buy it was the price. With a fresh drive train, rust free body, decent paint, and no mechanical issues, I picked it up for $4,000 (less than what he would have sold it to a non-family member for). I looked up the value online, and although it may not be 100% accurate, I believe low retail was around 9k, average retail was about 15k, and high retail was upper 20s? Seems kinda high to me...but it makes me feel like I got it for a steal.
You did fantastic on the price for a rust free car with a fresh drivetrain. You have the right idea.....just drive it until it has an issue. No sense pulling out a good running engine. Hopefully the pistons were spec'd for more compression when the engine was rebuilt. The club has a sponsored dyno day at St. Paul Automotive in May and that would be a good time to get it on for a VERY reasonable cost. I'm hoping to have mine on the dyno this year too and check out the new mill.... It would be really cool to have a posi in it by them too but I don't foresee that happening. 300+ hp on one tire might create a lot of squeeling on the rollers....
I went to the Dyno Days last year, and it was awesome. I was hoping I might be able to get the T/A on the rollers this year, but I believe Camaros have priority. If there are any open spots after everyone who wants to run has signed up, then I would love to get her on there.
Just sign up when the time comes. Craig ran his land yacht Buick last year. As long as you are a paid member and that's the car you have, bring it on ...
Ha, land yacht...Yeah, I remember that. He wasn't too impressed with how it performed either, if I remember correctly. Looks like I'll have to sign up then when we get closer to it.
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