I have a low mile rebuilt 403 with 4A heads, mild torque cam, stock intake, dished pistons -- pretty much a stock build. I am wanting to put it in my 64 Dynamic 88 or maybe my 63 Cad CdV so big heavy cars both with 2.94 gears and 225 75 15 tires 2.48 first gear TH400 and no OD.

Question is: if the factory CR was 8.0:1 (and some say lower) and it is now bored .030 over with a thicker head gasket than stock (felpro should be about .045) I am probably pushing more like 7.8:1 CR. This just seems unacceptable to me. All the info I find is for building HP with these engines but I just want a strong pulling off idle flat torque curve lower RPM high way cruiser. I have a set of #2 330 heads and a set of #6 350 heads I could build, both sets have the smaller valves than the 4A. Do I really need to add the bigger valves to these heads? Or a 2711 intake? Dual exhaust? Remember I rarely wind my engines above 3500 to 4000 RPM. Am I over thinking this?

 

With a 64cc chamber, pistons .025" below deck and the Felpro gaskets will put you around 9.5 to 1. A 68cc chamber will put you around 9 to 1. You need figure out how much below deck the pistons actually are. The small valve early heads flow the same as the 4A on the intake size as is and much better on the exhaust side, stock. I just had 9+ to 1 403 with #6 heads with 2.07/1.56 valves, the 204/224 cam and 2.78 open gears 28" tall 275/60R15 in my 70 Cutlass. Fun 1/4 block burnouts with a 2350 stall and very weak off the line with the factory 1650 stall. Do a 2000ish stall converter for more fun.

 

Thanks for the response. Great to hear i don't meed to install bigger valves. Sounds like a higher stall will help the engine get into its torque curve. Do you think the higher stall will affect high way cruising efficiency?

Full disclosure: I am really aware that as i get older I will never finish all my projects at the rate I am going. Throwing money at stuff is not an option right now and I highly need to build with the piles of parts I already have instead of buying more.

Now, having said that I do have a TH350C I could rebuild with shift kit and higher stall converter and then with the flick of a dash switch go into lock up and drop about 200 rpms. The other thing i am aware of is that sometimes you have to spend money to do it right the first time. What do you think of the Th350C idea.

 

Yeah, you may have a little more slippage with a higher stall, depending on the quality of the converter. Yes, the lock up converter on the TH350 will drop highway rpm 200 to 300 rpm. Just make sure there isn't a stud near the cooler lines, makes it a TH250C. What cam do you have?

 

True dual exhaust will absolutely benefit a healthy smog era engine, significantly. (16.20 to 15.80 in the 1/4 mile on a stock 79 Trans Am 403) https://www.curbsideclassic.com/blog...-trans-am-fly/

Heavy tanks like a Dynamic 88 or Cadillac Coupe Deville. Are cars best motivated with a TH400. Depending on model the Dynamic is 500-600 lbs less, so definitely the better option if going TH350. And the TH350 also eats less HP than a TH400, although dual exhaust offsets this issue.

As olds 307 and 403 mentioned with a better torque converter and gear ratio either car will perform better. It's the "smoke and mirrors" so to speak that allowed the aftermath of the smog era, Hurst/Olds and 442s to have somewhat decent performance. The fact that both cars you are considering are 2.94 is great. The Trans Am I mentioned above had a 2.41 rear for both passes.

 

As I've noted previously, the 403 flows as much air as a 400 BBO. The SBO ports and intake on the 403 is the biggest problem. Get some BBO heads, a port-matched SBO Performer RPM, and mill the heads to get the CR you want.

 

I am uncertain about exact cam specs but I do know the guy I bought this engine from (he built it) said it was a mild torque cam, nothing aggressive at all and probably close to stock but not the smogger. I have a new timing chain installed straight up.

 

Thanks for the link to that TA build experience and the dual exhaust upgrade. I remember reading that about a year or so ago when I bought this engine and was figuring out what to do with it. Most everything on the web one finds is about improving performance at the strip. I really just want to maximize what I have as a low rpm high way cruiser that is efficient yet powerful in the the torque curve where I need it -- around 2000 to 2500 rpm. I do think some dual exhaust around 2.25" (or maybe 2.5") will help me get there. I also have, for both cars, diffs with 3.21 gears, one from my 63 Starfire parts car and could consider that potentially. I know the TAs had 2.41 gears -- always seamed strange for a "performance" application although I believe they ran smaller dia. tires and 14" wheels.

 

Thanks all: After consideration I believe the 403 needs to go in the lighter car and the Cad 500 I have goes in the Coupe dV. I thought of an Olds engine (which will fit easily) as the week of crawling around under that car with a tape measure told me 500 is not an easy install with the X frame. Exhaust to steering box issues, oil pump and K member issues, Oil pan and steering issues, fan and radiator issue... the 500 is huge. None of that is insurmountable: I have it all figured out how it will be made to fit but unfortunately lots of money is part of the solution equation. The Olds engine are way simpler to swap if unconventional for a Cad. I think the 403 TH350C goes in the Olds and I save my pennies and put the 500 TH400 in the Cad.

 

I’m guessing you mean dot to dot?

 

Yes, I mean the timing chain is not advanced or retarded. Dot to dot is a better way to describe it. Good call, that could be a problem for someone not in the know.

 

Dot to dot doesn’t mean straight up, nor does saying it’s not retarded or advanced. You don’t know that until you check it. See “brothergood/cam timing”. Great example.

 

Don't let that discourage you, I would just take what you need from the information. Strip performance specs are the absolute end result of the quest for better performance. Whether it's flipping the air cleaner lid or an all out 100% increase in power build. Stating what it does gives us definitives. Even if you never get to or care to go to a track.

Precisely what the 403 was created to do. Behave like a big block in small block clothing... Dual exhaust just allows it to be all it can be. In the case of the 403s common factory specs 185 HP @ 3600 RPM and 320 LB FT at 2200 RPM. Dual exhaust raises both stat lines while maintaining its low RPM operating status. Just adjusting the numbers to what happens to an Olds 350 when you go from single to dual exhaust. You will gain 20 and 25 on the tally respectively in each category and only go up 400 RPM on both ends. So 205 HP @ 4000 RPM and 345 LB FT at 2600 RPM. This does not account for the lack of a catalytic converter, or the fact that 403s have the extra cubes, or your better cam... And that's just about a spec match for a 1974 (pre-catalytic converter) Olds 455, 210 HP and 350 LB FT. That 455 was powering cars weighing 700 lbs more than the Dynamic, and swiftly at that.

 

One of the pillars of the dead zone known as malaise era, 1973-1983. Performance in name only !

I really want to delve into this but I do not want to take away from your thread. I may start my own on the subject.


Sounds great ! I had a 100,000 mile 1971 Eldorado with its original 500 CID, about 20 years ago. Previous owner was a mechanic. A driver, she looked ok but ran lights out. Overall the most impressive feeling car i've ever owned or been in. You really felt like you were driving something special, grandiose.

 

If you are asking whether I degreed the cam or not, then, no I did not. I concede that it is not the best nor proper way to install a cam and timing chain.

 

Thanks for the encouragement. This is why I love the Cad 500. (And 455 Buicks Pontiacs and Olds. I have a 455 in my 67 Firebird vert.) This is my first 403 to play with and it's been fun learning as I go.

 

Does this apply to the earlier #2 330 heads as well as the #6 350 heads as far as flow characteristics go?

 

Yeah, they are very similar, flow wise. Basically rebuild whichever head is in better shape and CC where you want for combustionchamber size. The one advantage of the 70 heads is the readily available 5/16" rocker arms and bridges. Pretty sure the #2 use 3/8" rocker arms bolts. Something to be aware of if you plan on using the non adjustable rocker arms.