Want to wake up my 73 Newport Custom
- Thread starter badvs3vil
- Start date
You can... But you have some limitations.
The 8 1/4 has to be set up in the car. Not a huge deal, but the 8 3/4 is easier because you just have the center section to swap in and out. The 8 3/4 is also stronger and easier to obtain gears and parts.
From reading your posts, I think you need to take a step back... 3.23 is a great all around ratio. I used to use that ratio in my C body tow cars 40 years ago. It won't kill you at the pump, but it will "wake" the car up. 3.55 is also a good gear, but IMHO, the 3.23 is going to do what you want.
I'd advise against 3.9 gears... I've run them in street cars and they get tiresome. The car is nosier, eats more gas etc. Your engine is turning about 30% higher RPM. You also haven't talked about a sure-grip rear. Get up into that ratio and suddenly you are frying one tire if you stay with the open rear.
Again, 3.23 now gets into a good compromise. You really aren't going to be building a rocket ship here... It's a heavy car with a basically stock, low compression engine. Want to go with more gear? Look at camshaft and torque convertor too just to start.
So, find an 8 3/4 rear if you want to go all out. Find a sure grip too. It is a better rear. Want to keep it mild, I'll go against my advice and tell you to stay with the 8 1/4 and find some gears.
badvs3vil
Active Member
Thanks Big John! This gives me some ideas!
lemondana
Active Member
Post a few pictures of the left side of the carburetor with the air breather removed, and the kickdown linkage and throttle bracket. Since the 73 400 didn't come with a 4 barrel, your kickdown could possibly not be functioning correctly.
lemondana
Active Member
Very nice Newport, by the way.
The biggest thing with the 400s is their low compression. Which can need either small chamber cyl heads or aftermarket pistons to alleviate. Nothing over about 9.5 cr, though. Small chamber B/RB heads might be the easiest thing to do in that respect.
A bigger cam can be problematic. Too big and you loose the lower end performance and gain top end. Not big enough and your factory cam suddenly becomes better. Going to the 10.75" stock torque converter can help, too. Both of which can be helped by the 3.2 rear axle ratio.
Using a cam similar to the factory HP cam would work best, but the 3.2 rear axle would also help get the motor into the "power range" quicker than the 2.7 ratio does. The other side of the deal is that the factory HP cam, compared to the normal stock cams, may not be that miuch better in additional duration and lift. In one respect, you might already be closer to that power level with your exhaust system and aftermarket induction system and not know it.
Cyl heads would be an easier thing to do. Just don't get huge runners so that you keep enough port flow to maintain existing lower rpm throttle response, yet gain additional flow for a bit better higher rpm performance.
Enjoy!
CBODY67
A bigger cam can be problematic. Too big and you loose the lower end performance and gain top end. Not big enough and your factory cam suddenly becomes better. Going to the 10.75" stock torque converter can help, too. Both of which can be helped by the 3.2 rear axle ratio.
Using a cam similar to the factory HP cam would work best, but the 3.2 rear axle would also help get the motor into the "power range" quicker than the 2.7 ratio does. The other side of the deal is that the factory HP cam, compared to the normal stock cams, may not be that miuch better in additional duration and lift. In one respect, you might already be closer to that power level with your exhaust system and aftermarket induction system and not know it.
Cyl heads would be an easier thing to do. Just don't get huge runners so that you keep enough port flow to maintain existing lower rpm throttle response, yet gain additional flow for a bit better higher rpm performance.
Enjoy!
CBODY67
badvs3vil
Active Member
No issues there, I had to keep testing and adjusting till I had it shifting correct when I change out the throttle and linkage.
Ignition timing set to what the engine wants will give a good off idle acceleration.
You may have to recurve your distributor, I have some low compression engine running 20 deg initial with 36 total. then a make sure your vacuum advance is hooked up and set correctly.
In the picture at the car show, it looks like you need a front end alignment.
You may have to recurve your distributor, I have some low compression engine running 20 deg initial with 36 total. then a make sure your vacuum advance is hooked up and set correctly.
In the picture at the car show, it looks like you need a front end alignment.
USSMOPAR
Active Member
That is a very nice car. How big is your wallet?
Changing rear end ratios is not that good of an option.
You are not driving a muscle car. Even then my muscle car would have 3.23 unless it was a 5 speed and then it would be 4:10. Do the math
There is nothing wrong with the rear end ratio.
aluminum dual plane intake
HP manifolds or better yet headers
tight timing chain
dual exhaust
tune up
synthetic fluid in the rear
The torque converter is the deal breaker. Spend your money there even if you don't spend it anywhere else. Be sure to use an external trans cooler. You will be amazed and the car can run 80 nice on the interstate with goood mpg
Changing rear end ratios is not that good of an option.
You are not driving a muscle car. Even then my muscle car would have 3.23 unless it was a 5 speed and then it would be 4:10. Do the math
There is nothing wrong with the rear end ratio.
aluminum dual plane intake
HP manifolds or better yet headers
tight timing chain
dual exhaust
tune up
synthetic fluid in the rear
The torque converter is the deal breaker. Spend your money there even if you don't spend it anywhere else. Be sure to use an external trans cooler. You will be amazed and the car can run 80 nice on the interstate with goood mpg
badvs3vil
Active Member
Interesting. So I already have new short tube headers and all new dual exhaust. Already has a new tune up, I guess I could always curve the distrib as well. You think 2.71 GR is ok?
As far as a Torque Converter, that seems like something I could and probably should to be honest as my rear main seal is leaking. I could fix that while I am in there. Any ideas on what I would look for in a Torque Converter for this thing? I also currently do not have an external trans cooler, so that's something else I could do.
Side note, even though this is a 73 the 400BB engine is from 77 according to the casting on the block. Not sure how much that matters when dealing with the TC.
6PKRTSE
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I have a little ole 175 shot of nitrous on mine. Fun to take out the Mustang, Camaro and some corvettes.
twostick
Senior Member
Are you sure that's an 8.25 diff? My 73 had a 9.25 and that is all I have ever seen under a late Cbody.
To finish waking up your 400, get the distributor recurved if you haven't already. This is assuming it's the stock one. You will need to limit the advance travel by having the slots in the fly weights welded up. You want total advance to be 34 degrees all in by 2500 rpm or less with as much initial as it will take without kicking back on the starter when it's hot. 15 to 18 deg BTDC is probably where you will wind up for initial and then you can file the slots to get you 16 to 19 for your 34 degree total. Get an advance spring kit and play with different spring combos to get your curve dialed in.
If you are still running the stock cam, get a performance timing chain and gear kit with multiple keyways so you can advance the valve timing 4 degrees. Contrary to what the service manual says, the compression ratio is actually in the low to mid 7:1 range. Advancing the cam will pick up bottom end torque noticeably especially when combined with the distributor recurve.
These 2 modifications cost very little and if the timing chain is original, it needs to be changed anyway because the nylon gear teeth are probably cracked or broken.
Take it for a drive and see if that puts a little more swagger in its attitude.
After you get bored with that performance increase, get a 3.21 gear, preferably with a Sure Grip and enjoy the transformation.
Kevin
To finish waking up your 400, get the distributor recurved if you haven't already. This is assuming it's the stock one. You will need to limit the advance travel by having the slots in the fly weights welded up. You want total advance to be 34 degrees all in by 2500 rpm or less with as much initial as it will take without kicking back on the starter when it's hot. 15 to 18 deg BTDC is probably where you will wind up for initial and then you can file the slots to get you 16 to 19 for your 34 degree total. Get an advance spring kit and play with different spring combos to get your curve dialed in.
If you are still running the stock cam, get a performance timing chain and gear kit with multiple keyways so you can advance the valve timing 4 degrees. Contrary to what the service manual says, the compression ratio is actually in the low to mid 7:1 range. Advancing the cam will pick up bottom end torque noticeably especially when combined with the distributor recurve.
These 2 modifications cost very little and if the timing chain is original, it needs to be changed anyway because the nylon gear teeth are probably cracked or broken.
Take it for a drive and see if that puts a little more swagger in its attitude.
After you get bored with that performance increase, get a 3.21 gear, preferably with a Sure Grip and enjoy the transformation.
Kevin
commando1
Old Man with a Hat
While I'm still recommending 3.23 ratio, if you want to go to 3.55 and stay with the 8 1/4, here's a deal on some used gears. [FOR SALE] - Chrysler 8.25 3.55 Ring and Pinion
Used gears can sometimes be noisy and that needs to be remembered, but then again, they may not be. Might even be better than some of the new stuff out there. If in good shape, that price can't be beat.
badvs3vil
Active Member
man people bought those so fast. I didn't even have a chance! LOL
badvs3vil
Active Member
Well, how about this? - 1973 CHRYSLER NEWPORT Motive Gear C8.25-321 Motive Gear Ring and Pinion Sets | Summit Racing
3.21 @ 8.25?
I haven't bought anything like that in years, so I'm not one to comment if that brand is good or bad.
I see that Motive Gear and Richmond Gear are owned by the same company.
USSMOPAR
Active Member
Timing chain, tune up Yes! The advice on 3.23's is poor at best even with 27 inch tall tires. It is very expensive to change ratios and not recommended.
The torque converter needs to be chosen by the cruising rpm of the car - you want the converter past the stall speed at the chosen rpm. External trans cooler is a must. I have owned large barges and towed a car trailer with them without problems even up and down steep hills using 3.23 gears and a good converter.
Engine torque and hp actually determine where it will really stall. The advice i have always been given - you can never have enough converter...The last customer car was a mild 360 T Quad with 340 exhaust in a R body with the lock up converter. 2.94's with a 3500 rpm rated lock up converter. What a beast! And MPG to boot 22 mp highway at 75 mph
spark plug wires...don't be cheap like many on here.
Firecore or say home
The torque converter needs to be chosen by the cruising rpm of the car - you want the converter past the stall speed at the chosen rpm. External trans cooler is a must. I have owned large barges and towed a car trailer with them without problems even up and down steep hills using 3.23 gears and a good converter.
Engine torque and hp actually determine where it will really stall. The advice i have always been given - you can never have enough converter...The last customer car was a mild 360 T Quad with 340 exhaust in a R body with the lock up converter. 2.94's with a 3500 rpm rated lock up converter. What a beast! And MPG to boot 22 mp highway at 75 mph
spark plug wires...don't be cheap like many on here.
Firecore or say home
To much info here but a 8.25 is good up to about 500 HP. Find a jeep and grab a 3.55 track lock drops righ in. Drawback the ring gear has a different pattern than mopar but that is only if you want to change the ratio.
The 8 1/4 thread | For A Bodies Only Mopar Forum
Also check your curve in the distributor. Best bang for the buck if it right like two stick mentioned. Most aftermarket ones have a cure that come in way to fast so figure out what you need first.
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