Moparts
Are 3.91's enough gear?
Posted By: VITC_GTX
Are 3.91's enough gear? - 07/24/09 02:48 PM
My GTX performs so-so at best (for a mild 440). It has poor performance off the line and until the RPM get up there. Carb, cam, converter and gears seem to be the problem (see below). This car is 100% street and I don't care about gas mileage.
If I go to 3.91's and maybe a ~3000 converter would that wake up my combo or do I need to get more drastic?
Here are the specs:
'70 GTX
Mild 440
Stock compression forged pistons
Polished and balanced rotating assembly
Mildly ported 906 heads
284/484 MP cam
Eddy RPM Performer intake
Stock manifolds, 2.5" exhaust
FBO electronic ignition
727 w/340 convertor (guessing 2300-ish?)
3.55 Suregrip
275/60-15 rear tires (28" tall)
Posted By: Noblewk
Re: Are 3.91's enough gear? - 07/24/09 03:00 PM
I would leave the Gears alone and just change the Converter. You say its 100% Street, and the 3.91's will have you buzzing down the freeway ~3300 rpms.
Posted By: challenger70
Re: Are 3.91's enough gear? - 07/24/09 03:02 PM
are you sure you don't have any problems? Even that combo should boil the hides pretty good. I have 3.91's xterme energy cam (.492 lift I think)and a 3,400 stall and it decimates my drag radials and blows ls-2 vettes away. I would think your combo would be better than you describe.
Posted By: Dodgem
Re: Are 3.91's enough gear? - 07/24/09 03:21 PM
First problem is the TQ as that cam needs a 3000 to 3500. 3.55 to 3.91 gear change will give a little but not much.
I'll bet your cam could use degreeing and a little advance from suggested intake centerline install.
If it is the 108 lobe separation and a 106 intake install it would really respond to 103 or 102 intake install.
often when a 484 108 lobe center is lazy the cam is in at a slightly retarded position.
Posted By: VITC_GTX
Re: Are 3.91's enough gear? - 07/24/09 03:35 PM
My main reason for thinking of this was because of this thread I started on my carb. Most folks said to change the cam (not what I want to do) or add gears and a converter.
https://board.moparts.org/ubbthreads/show...rue#Post5253122
Posted By: buildanother
Re: Are 3.91's enough gear? - 07/24/09 03:42 PM
I would get the converter upgraded.
(changed)
Posted By: challenger70
Re: Are 3.91's enough gear? - 07/24/09 03:48 PM
If your sure your combo is healthy a stall should help alot. My car is 100% street and with a good converter running a 3,000+ stall should not be a problem. I was a little concerned myself about a higher stall on the street but it drives like a creampuff until you stand on it. The 3.91's with a 28 inch tire isn't terrible on the highway if you stick to 60-65, it does get buzzing pretty good over that though. My combo is just a little bigger cam, stall and gear more than yours but it sounds like worlds apart as far as performance, your sure theres nothing else wrong?
Posted By: demon440
Re: Are 3.91's enough gear? - 07/24/09 03:51 PM
I think you should finish one car before you
tear apart another.
Don't you have 2 or 3 projects going on right now?
Or you could sell me your Demon.
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Posted By: jbc426
Re: Are 3.91's enough gear? - 07/24/09 03:58 PM
What is your compression ratio? If your tune is good, the right converter and cam will do wonders with 3.54's.
What do you have the timing set at, initial and total? What do your plugs look like? You can easily change the cam and lifters with the motor in the car without removing the intake. You can always contact Dave over at Hughes Engines and talk to him about your set-up and see what he recommends.
Posted By: MNobody
Re: Are 3.91's enough gear? - 07/24/09 04:05 PM
Nobody thinks the stock exhaust manifolds might be an issue? I had a 440 in my 69 charger with 10:1 flat tops, stock heads, Crane .484 cam, Torker 2 manifold, 850 dbl pump, Cyclone headers , 2 1/4" exhaust, accel dual point mech dist and 3:23 gears...that thing would roast the tires if you wanted to and would eat 5.0 mustangs and 350 vettes for breakfast back in the day....
Posted By: mark7171
Re: Are 3.91's enough gear? - 07/24/09 05:01 PM
Make torque power. Go 3.55 gear at most with a 4 speed. Let the 3.75" crank pull you, but compensate with a timing curve. Keep a performer dual plane at all cost. Try a 800 AVS thunder, or 650DP both manually actate the secondaries. Also taylor top end with a spacer.
Posted By: ademon
Re: Are 3.91's enough gear? - 07/24/09 05:25 PM
probably low on CR maybe in the 8.5 zone, that doesn't help with that cam, the exhaust manifolds are not the problem many F.A.S.T. cars running low 11's with them. maybe advance the cam, make sure the FBO stuff is working.
Posted By: mark7171
Re: Are 3.91's enough gear? - 07/24/09 05:37 PM
why that cam with a stack compression ?
Posted By: DaytonaTurbo
Re: Are 3.91's enough gear? - 07/24/09 05:39 PM
Torq converter cam make a world of difference. Not sure who's good now, but I know dynamic used to make a good street/strip converter that'd flash stall to 4-5k yet drive basically normally during regular driving. Something like that would be a night and day difference for your car. If you go to a high stall like that, you can leave your rear gears as-is. If you do the stall, the gears won't make much of a difference.
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the exhaust manifolds are not the problem many F.A.S.T. cars running low 11's with them.
True, but the fast guys are also going to be running ported manifolds, higher compression and often stroker cranks. But for his application HP manifolds should do the job decently.
Posted By: 540challenger
Re: Are 3.91's enough gear? - 07/24/09 05:52 PM
You could also get a shorter tire 26" a 275/50/15 They are a little wider i think about a 1 inch off the top of my head.
Posted By: challenger70
Re: Are 3.91's enough gear? - 07/24/09 06:21 PM
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You could also get a shorter tire 26" a 275/50/15 They are a little wider i think about a 1 inch off the top of my head.
it would be a real easy way to see how your car likes a higher gear and free if you could borrow a set.
Posted By: Mr.Yuck
Re: Are 3.91's enough gear? - 07/24/09 06:30 PM
284/484 MP cam <--- that be your problem... and if you have a carterbrock carb. 3.91's and more conver will help. or you can swap the cam out for something a more street friendly. I'd do the cam...much easier and cheaper.
Posted By: Mr.Yuck
Re: Are 3.91's enough gear? - 07/24/09 06:31 PM
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You could also get a shorter tire 26" a 275/50/15 They are a little wider i think about a 1 inch off the top of my head.
it would be a real easy way to see how your car likes a higher gear and free if you could borrow a set.
a 26" tire on a B-body would look silllllllly.
Posted By: GTX MATT
Re: Are 3.91's enough gear? - 07/24/09 07:43 PM
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Nobody thinks the stock exhaust manifolds might be an issue?
Posted By: Mr.Yuck
Re: Are 3.91's enough gear? - 07/24/09 08:04 PM
The mani's are NOT the issue. While tha manis are not the best for performance, that cam is what is making the car poo poo. Trust me. Swap the cam out, even with a summit 488 cam and you will be much much happier. You won't need 3.91's (although they'd help) and you won't need to change your convert. That 484 cam sucks compression and won't start workingh until 3200rpm. Which means it's DOG off the line. Plenty of cams will work w/ your set-up get one that will work and you won't need to drop the trans or pumpkin.
Posted By: Noblewk
Re: Are 3.91's enough gear? - 07/24/09 08:07 PM
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Nobody thinks the stock exhaust manifolds might be an issue?
I'm thinking since he states "It has poor performance off the line and until the RPM get up there." that the exhaust has no effect. Headers or Performance Exhaust has very little effect with low end "Grunt".
The cam has moved the Torque "LOW END Grunt" into a higher RPM Range.
A different Torque Converter that would allow the engine to "Slip into" the higher RPM Range should clear up his issues.
Posted By: Dougsmopars
Re: Are 3.91's enough gear? - 07/24/09 08:48 PM
That cam isn't that radical. I agree with previous that you should check cam timing. A good 2800-3000 stall should be plenty in a 440. Is your intake a dual plane? If not lose it and get a dual plane. Remember basically stock 440's don't make power over 5000-5500. There torque monsters down low. A bone stock 440 with 3;23's should roast the tires off.
Posted By: moper
Re: Are 3.91's enough gear? - 07/24/09 09:27 PM
Your approach is similar to repairing a hole in a dam by adding berms to direct the flooding better... The issue is the cam is wrong. The 484 sounds small, but it has big duration numbers for its size and the rest of the engine can't support it. Therefore it can't support the car. You are looking at hundreds for a gear and convertor swap, or either by itself... Why not spend a few hundred on the right cam? If it's too much for you to handle, find a reputable shop to do it for you. You'll be much happier. It's a dog down low. It's still a dog when you rev because of the manifolds and the lack of compression. So instead of making it a dog you're going to try to minimize the dogginess? So what's the real reason your fear changing the cam? Is it an engine warranty issue or something? The package is perfect for what you do except for the cam. $300 in parts, maybe $400 in labor to pay a shop, and it's fixed permanently. $700 is a little more than buying a used chuck and installing it yourself, and a lot less than buying a convertor with that rear and installing both or having them installed.
Posted By: Mr.Yuck
Re: Are 3.91's enough gear? - 07/24/09 09:55 PM
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That cam isn't that radical. I agree with previous that you should check cam timing. A good 2800-3000 stall should be plenty in a 440. Is your intake a dual plane? If not lose it and get a dual plane. Remember basically stock 440's don't make power over 5000-5500. There torque monsters down low. A bone stock 440 with 3;23's should roast the tires off.
The cam is ALL wrong. He'd be better off w/ a stock 440 cam than that 484. It is a bracket racing cam. It needs 10:1+ 3000+ stall 3.91's or better, intake, headers and the rest to work. Trust me a stockish 440 w/ 3.55's and that cam will net you a slow, non tire spinning B-body.
Posted By: buildanother
Re: Are 3.91's enough gear? - 07/24/09 11:45 PM
Until you put a 10" converter in it.
Posted By: forphorty
Re: Are 3.91's enough gear? - 07/24/09 11:53 PM
I dont know a thing about the 484 cam, but i think 383man ran it in his sons dart with almost stock 383 and ran 12.30s. Big cams in low compression 440s can run well. Throw a 3500 stall in it and it will feel like a different car. Then if you are still unsatisfied with the performance you might consider a cam change.Even if you choose to put a smaller cam in it, the convertor will be a big boost.Should be an easy 13 sec car with street tires,12s with slicks. BUT, before you spend any real money, make sure what you have now is tuned properly.
Posted By: VITC_GTX
Re: Are 3.91's enough gear? - 07/25/09 02:11 AM
Quote:
I think you should finish one car before you
tear apart another.
Don't you have 2 or 3 projects going on right now?
Or you could sell me your Demon.
Oh, that hurt 
Yeah, I have two in bare metal and one in primer... 
Posted By: VITC_GTX
Re: Are 3.91's enough gear? - 07/25/09 02:15 AM
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What is your compression ratio? If your tune is good, the right converter and cam will do wonders with 3.54's.
What do you have the timing set at, initial and total? What do your plugs look like? You can easily change the cam and lifters with the motor in the car without removing the intake. You can always contact Dave over at Hughes Engines and talk to him about your set-up and see what he recommends.
Compression is stock (advertised 10.0:1) with the heads shaved .030". Not sure what actual would be...
I think timing is ~18 initial 35 total (or close to it) on FBO advise.
Posted By: VITC_GTX
Re: Are 3.91's enough gear? - 07/25/09 02:20 AM
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284/484 MP cam <--- that be your problem... and if you have a carterbrock carb. 3.91's and more conver will help. or you can swap the cam out for something a more street friendly. I'd do the cam...much easier and cheaper.
I guess everyone's different but I would rather change a converter and rear end than a cam.
I hate cracking the motor open (nicely painted, etc) and I love the lope of the cam. The sound is the best part of the car.
Posted By: VITC_GTX
Re: Are 3.91's enough gear? - 07/25/09 02:21 AM
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You could also get a shorter tire 26" a 275/50/15 They are a little wider i think about a 1 inch off the top of my head.
it would be a real easy way to see how your car likes a higher gear and free if you could borrow a set.
a 26" tire on a B-body would look silllllllly.
But it would be a good way to see how it would run with lower gears.
Posted By: RUNCHARGER
Re: Are 3.91's enough gear? - 07/25/09 03:00 AM
I think a convertor would be the best fix. Lower gears aren't necessary and that cam would like more stall. That's assuming the tuneup is right.
Sheldon
Posted By: B5 Bee
Re: Are 3.91's enough gear? - 07/25/09 03:14 AM
The 484 cam is bigger than most think, you need more compression. If you want more low end power, cut the heads and install the cam at 106*.
Fix the motor first, then tune the converter and gear to it if needed.
Posted By: MNobody
Re: Are 3.91's enough gear? - 07/25/09 03:26 AM
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You could also get a shorter tire 26" a 275/50/15 They are a little wider i think about a 1 inch off the top of my head.
it would be a real easy way to see how your car likes a higher gear and free if you could borrow a set.
a 26" tire on a B-body would look silllllllly.
But it would be a good way to see how it would run with lower gears.
I had l-60-14's on my 69 Charger, it didn't look bad 
Posted By: RTSrunner
Re: Are 3.91's enough gear? - 07/25/09 04:08 AM
We rebuilt a '69 GTX 440 to stock specs,except used a 484 Mopar cam.Stock Carter AVS carb,iron intake and exhaust manifolds,906 heads unported-stock valves,only a .030 overbore.2-1/2 exhaust through Dynomax turbo mufflers.Auto 727 with a custom converter,mild stall.Initially it ran the stock 3.23 gear,then 4.10 gear.The GTX ran a 13.9 with the 4.10 gear,in drive shifts at 6200 RPM,never ran it with the 3.23.Tires are BFG 295/50/15's on 10" Weld wheels.The car has A/C and a choppy idle,but ok with the air on.It runs good with the 4.10's,but I always wanted to try it with a 3.55,the 3.23 gave it awesome top end and highway passing power though.I have tuned many stock or near stock 440's and think a 3.55 gear is perfect for an all around driver.The cam as installed may be your low end problem,you could try to advance the cam timing by 4*.BTW the 484 cam in the GTX will shred the tires!(I may have the gears backwards for the dragstip time,it may have been with the 3.23's)I'll check,it is a friends car,and the times were in the early '90's.
RT
Posted By: R70RUNNER
Re: Are 3.91's enough gear? - 07/25/09 05:00 AM
It's the cam, or you need more compression.. which do you want to fix? The 440 can handle the .484 but needs real 10:1 not Morpar magic wanna be factory maybe 9:1 that you have... I'd swap the cam
Posted By: forphorty
Re: Are 3.91's enough gear? - 07/25/09 05:16 AM
Posted By: 11secondC
Re: Are 3.91's enough gear? - 07/25/09 06:25 AM
1967 VIP 4400 lbs w/driver =
14.17@97, 2.08 60', worn out stock bottem end '62 413, 484 cam, 452's, 750 Carter + RPM, 1.75" headers, 2400 stall, 3.55's, 26" BFG's and it would boil those anywhere in first gear...
Posted By: Mr.Yuck
Re: Are 3.91's enough gear? - 07/25/09 12:53 PM
rather do a convert and rear than a cam??? come on over you can pull my trans and put n a 3k convert for me and I'll do your cam...lol
Really the 484 while some claim in runs well in a low comprssion non-geared car would be suprised how uch better their car would run w/ the right cam in it. Just because you can do a burn out doesn't mean the car is running it's best. If you are careful and clean as you go the engine won't get all nasty. A cam swap is probably your cheapest and best way to go. If you want to keep the 484 you'll need a 3k convert, 3.91's, headers, at least 2.5 exhaust, and probably nothing smaller than a 750DP carb. Also try advancing your timing to 38* @ 2200. Un-hook the vac advance.
Posted By: Mr.Yuck
Re: Are 3.91's enough gear? - 07/25/09 12:58 PM
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We rebuilt a '69 GTX 440 to stock specs,except used a 484 Mopar cam.Stock Carter AVS carb,iron intake and exhaust manifolds,906 heads unported-stock valves,only a .030 overbore.2-1/2 exhaust through Dynomax turbo mufflers.Auto 727 with a custom converter,mild stall.Initially it ran the stock 3.23 gear,then 4.10 gear.The GTX ran a 13.9 with the 4.10 gear,in drive shifts at 6200 RPM,never ran it with the 3.23.Tires are BFG 295/50/15's on 10" Weld wheels.The car has A/C and a choppy idle,but ok with the air on.It runs good with the 4.10's,but I always wanted to try it with a 3.55,the 3.23 gave it awesome top end and highway passing power though.I have tuned many stock or near stock 440's and think a 3.55 gear is perfect for an all around driver.The cam as installed may be your low end problem,you could try to advance the cam timing by 4*.BTW the 484 cam in the GTX will shred the tires!(I may have the gears backwards for the dragstip time,it may have been with the 3.23's)I'll check,it is a friends car,and the times were in the early '90's.
RT
I ran the sumit 488 cam in a 67 coronet w/ a basic cast piston (maybe 9:1) 440. stock 906 heads, headers, RPM intake 750DP, 175K convert (2800) car ran consistant 12.90 @ 104. It had the 484 in it when I got it and 3.55's. what a dog. it could barley run 14.0's IMO for a 440 powered B-body that's too slow.
Posted By: forphorty
Re: Are 3.91's enough gear? - 07/25/09 09:24 PM
with 10in 3500 convertor ,12s with 3.55s isnt hard to do . 99.9 percent of performance engines want more convertor than what you have now. Keep in mind that a STOCK 440 magnum has a torque peak that occurs at 3200 rpm. I feel that the biggest thing holding you back enginewise may be the manifolds. A set of small headers(1 3/4 primary) will boost the power from the bottom to the top. I forgot what carb you have, but a 750dp works great on mild 440s.
Posted By: VITC_GTX
Re: Are 3.91's enough gear? - 07/25/09 10:24 PM
I'm going to keep the manifolds for the stock look. I may just call Kenny at PTC and give him my combo and see what he thinks about a converter swap.
I do have a Holley 750 DP on it.
Posted By: Mr.Yuck
Re: Are 3.91's enough gear? - 07/26/09 01:44 PM
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I'm going to keep the manifolds for the stock look. I may just call Kenny at PTC and give him my combo and see what he thinks about a converter swap.
I do have a Holley 750 DP on it.
Dude do yourself a huge favor from somebody who's been down your road. Change the cam and be done. It will run better, sound better and be much more driveable, not to mention FASTER.