Olds 403 in 1988 Cutlass - 326hp to wheels

[Rob]

Hi everyone,

I have a 1988 Cutlass Supreme with a rebuilt Oldsmobile 403.

Engine:

Olds 403, stock bottom end.
9.6 to 1 compression.
#5 heads from a '68 350 rocket, fully ported.
2.07" intake and 1.71" stainless exhaust valves.
Remanufactured 1977 quadrajet.
Comp Cams XE262H camshaft, 218/224 duration and .475/.480 lift @0.050 on 110LSA degreed, installed straight up.
Comp claims rpm range of 1200 to 5600rpm.
MSD Ready to Run distributor.
2.5" true dual exhaust, but through stock 403 manifolds.

Dyno results to the wheels were 326hp at 4500rpm and 403lb tq at 3820rpm, corrected.

Transmission:

Rebuilt TH200-4R with hardened parts from Art Carr. Lockup functioning. Stock torque converter.

Rear end:
7.5" with 28 spline axles, new posi unit and 3.23 gears.


I've got 2 questions:

This is the first time I've driven a car that makes power in the mid/high rpm range. I assumed that with all the power it's making, the low end would still be decent. However, when I tramp on the gas from a dead stop, there's no launch to the car, and it won't squeal the tires. The tires are only 215/70/14s besides. Once it hits around 2500rpm, it takes off like a rocket though. I've never run at the track, but 0-60mph takes roughly 6.5 seconds. The car accelerates in 2nd gear as quickly as in 1st, but only because idle-2500rpm is weak in 1st gear.

Does the camshaft make that big a difference in low rpm performance? Or is it possible that the carb needs adjustment for more off idle fuel or something?

The carb was tuned for WOT performance, but not nearly as much effort went into tuning for idle/part throttle. I've seen people with similar setups making less top-end power, but they're able to roast the tires from a stop.

One of the oversights was that I reused the stock torque converter. Art Carr sells a 12" lockup converter for $356, with a stall speed of 2200rpm. How would this affect the launch of the car?

 

[online170]

Re: Olds 403 in 1988 Cutlass

Hi Rob;

Welcome to the forum.

No! a mid/high range cam does not mean you have zero power off idle. It should still be a monster. I have only had one very tired engine that would not spin the tires. It had very little compression, 2.56 gears, and 28" tall tires. With the 14" tires you describe it should light them up pretty good. Stock converter or not... 326hp is plenty to light them up.


It sounds like a tuning issue.

What is your timing set at? Initial, total, and any vacuum? Sounds like your mixture is off, either too rich or too lean. Im not the best Qjet tuning guy, but the couple of things I do know about them;

1) The Qjet has a little lever that prevents the secondaries from opening until the carb is warm. This lever usually gets stuck and prevents them from opening.
2) The Qjet usually does not open the secondary butterflies all the way. You can bend the tang to make it open all the way. (They should have caught this if they tuned at WOT).
3) The air flaps over the secondaries have a little spring adjuster. You can tighten or loosen it if it isn’t opening quickly/slowly enough to eliminate the bog. (Again this is part throttle or WOT stuff, which sounds like its good).

 

[Rob]

Initial timing is 18 degrees.
Total timing is 34 degrees.
Vacuum can is hooked up and is providing a little too much vacuum, something like 20 degrees. Don't see how that would affect anything but part throttle cruise efficiency though, although maybe I'm wrong.
The weights/springs in the distributor were installed to give it a fast advance curve.

The carb was a remanufactured unit from Autoline. They are reputable, but since it's a 1977 carb, I would assume that everything was set up to 1977 specs. Olds engines of that era were low compression mediocre performance, so perhaps the carb isn't optimal to my build. WOT performance doesn't seem to suffer though ... especially given those stock manifolds.

The secondaries are opening completely. They were adjusted to do so during the dyno testing. How quickly they open I'm not sure about.

The response at part throttle feels unusual ... it's like the car only REALLY goes if you put it right to the floor. Is that the only time the secondaries open? If I push the gas pedal half way down or even 3/4 of the way, it's not nearly the same response. I'm saying it's unusual because my brother had a '96 Impala SS that wouldn't get traction if you gave it any more than 1/2 throttle, and it was mostly stock engine.

 

[BuWaGone]

Just tune thru trial and error. But my suggestions would be to put medium/light spring comb in the distributor. Back down the intial timing and go back up in two degree increments until it feels good.

Not sure about the carb cause I dunno jack about Q-jets. Sounds like it could be rich but how do you tune A/F on those?

Are you sure your trans is running prefect?

That cam in a 403 shouldn't need a stall convertor, it's a fairly mild cam with all those cubic inches.

 

[olds307 and 403]

My stock converter flashes around 18-1900 rpm, 2200 would be more ideal. My low compression 7.9 to 350 will burn one tire good. My 8 to 1 403 hit both hard with the locker. You could try 2-4 degrees more timing and rejet the carb. My stock 403 carb had 73 primary and 43K primary rods. The Holley reman had the same rods but 71 jets.

 

[L92 OLDS]

WOT performance doesn't seem to suffer though ... especially given those stock manifolds.

The secondaries are opening completely. They were adjusted to do so during the dyno testing. How quickly they open I'm not sure about.

The response at part throttle feels unusual ... it's like the car only REALLY goes if you put it right to the floor. Is that the only time the secondaries open? If I push the gas pedal half way down or even 3/4 of the way, it's not nearly the same response. I'm saying it's unusual because my brother had a '96 Impala SS that wouldn't get traction if you gave it any more than 1/2 throttle, and it was mostly stock engine.

Your build is similar to mine but has little less compression and cam. Q jets are great carbs for a street car and you should be able to tune it yourself for optimal performance. I experimented with mine and am very pleased with the results.

During WOT, a Qjet operates primarily on the secondary rods and air door so most anything you do on the primary side will have little effect. The secondary rods can be changed with the carb on the engine. Sounds like your problem lies with the primary circuit and rods though. I've heard that removing primary metering rods can also be done with the carb on the engine but I prefer to remove the carb and work on the bench. You should check your local library for a book on tuning Q jets...There are also some good ones at Barnes and Noble. Once you are familiar with Q jet operation it will be easy for you to modify and tune. Many people over the years have mistakenly removed their Q jet in favor of a gas sucking Holley because they weren't willing to learn the Q jets. Both are excellent carbs and each have their application.

 

[Rob]

I have Cliff Ruggle's book on tuning quadrajets. I've read through it but I've never had the courage to start adjusting anything. I also didn't know whether or not this is normal ... again, I thought the larger camshaft and its higher power band was to blame for the supposed lack of off-idle response. And just to confirm, this behavior is NOT normal for an engine of this potential, correct??

Cliff's book discourages the use of remanufactured carbs, since the companies usually assemble a "one size fits all" carb instead of tailoring it to the specific engine era. That's why I thought that my carb might be to blame.

Where does one find/order these new jets/rods? Are there any adjustments I should try before getting into the internals of the carb?

Besides the lack of tire squealing, are there any other "behaviors" that may indicate a problem? For example, the car occassionally stalls when I put it in gear and it's still cold, but then fires right back up and no issue the 2nd time. But it also has stalled when warm and I put it into reverse to back in the driveway. Idle is at 900rpm in park (warm) and 700rpm in gear, and 1400rpm when on the fast idle. Choke is functioning but almost seems like it's letting off too soon. Could this be related somehow?

Almost sounds like a fuel delivery issue for anything other than wide open throttle.

 

[FE3X CLONE]

The 403 in my '81 is very similar to your build. Cam has a little more duration but the original Crane Cams cam I had in it was close to what you have and with a 2200 stall converter that thing would go all over the place spinning the tires at will on the street. However at the track with the 215 series tires it managed to hit sub 2.0 second sixties. It does have a 3.73 gear though.

326HP and 403lb/ft with very little to no tire spin equals a fun bracket racer. 😉

 

[Rob]

Where do I go about getting these primary rods you speak of? And based on my engine specs, what would you recommend?

 

[techg8]

For Quadrajet Parts I would recommend http://www.quadrajetparts.com as the go-to source. They have about everything you would ever need for a Qjet.

Rods and jets are a part of the equation, but tuning the carb needs the whole shebang.

Idle tubes need enlarged and channel restrictor too.
idle mix screw holes to .081 or .092
Jet size needs to be relative to your air bleed size. Simply sticking in larger jets may cause over rich. Ruggles book covers this sizing well.
If you dont want to mess with the air bleeds I would just go up a size or two from the stock jets and go with K series rods about .030 smaller than the jets.
Check the open rate of the primary pulloff, it should open in about 1.5-2 seconds for your application. Too fast and youll bog. too slow and youll load up on fuel
air flap spring should be set about 1/2 turn tension
Also check the open distance of the air flaps, as was mentioned previously.
Put something along the lines of an AU secondary rod in there.

Make sure the secondary lockout is not keeping the secondary plates shut. Remove it if I were U.
Make sure the secondary throttle plates open full 90degrees at WOT. Adjust links as needed to achieve it.

thats what I think

Good luck