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krs1r/t
09-21-2009, 01:11 AM
408 motor with 456 gears good together or no? maybe stay with 392

mtlcafan79
09-21-2009, 01:13 AM
Depends on the cam, convertor, and if you have slicks or not. Mine with 4.10's and a 3200 stall would blow them off on the street all day long. At the track I felt like it could have used some more convertor/gear with a 28" tire.

bad360rt
09-21-2009, 01:23 AM
Ideally, you shouldn't worry about traction issues when considering gear selection. Gears should be picked to match your combo and get your rpms where you need them when crossing the line.

Also have to consider if you're going to spray it or not. For my setup, 4.56's would be perfect if I were staying all motor (along with more stall), but since I'll be spraying it, I'm going with 4.10s.

SB440R/T
09-21-2009, 01:25 AM
Ideally, you shouldn't worry about traction issues when considering gear selection. Gears should be picked to match your combo and get your rpms where you need them when crossing the line.

Also have to consider if you're going to spray it or not. For my setup, 4.56's would be perfect if I were staying all motor (along with more stall), but since I'll be spraying it, I'm going with 4.10s.

How high are you reving it to not run out of gear? You taking it into overdrive? Are you still running the 46re?

krs1r/t
09-21-2009, 01:31 AM
yes 46re, havent bought the converter yet, 456 have been in for 2 years now, solid roller cam and lifters so i can rev it pretty high

krs1r/t
09-21-2009, 01:33 AM
i also have 28 inch tall hoosiers slicks

bad360rt
09-21-2009, 02:06 AM
How high are you reving it to not run out of gear? You taking it into overdrive? Are you still running the 46re?

With the 4.10s and 28" tires it should cross the line around 6k on the motor and should be able to keep it under 7k on the bottle. I'll be shifting at around 6600 and keeping the o/d off. Still on the 46RE for now, eventually I want to put a 727 in it.

SB440R/T
09-21-2009, 02:09 AM
With the 4.10s and 28" tires it should cross the line around 6k on the motor and should be able to keep it under 7k on the bottle. I'll be shifting at around 6600 and keeping the o/d off. Still on the 46RE for now, eventually I want to put a 727 in it.

Shifting past 6k would scare me, but then again I don't have an R3. :jester:

bad360rt
09-21-2009, 02:20 AM
Shifting past 6k would scare me, but then again I don't have an R3. :jester:

T&D rockers and good springs help too. Only thing holding me back now is the fact that it's still a hyd roller, but peak hp is at 63-6400, so I don't need to go much past that anyway.

dakfink
09-21-2009, 08:54 AM
Shifting past 6k would scare me, but then again I don't have an R3. :jester:

WHY???

a Magnum Motor will hold a lot more than any of us have throwed at them so far. Especially in N/A trim.

RPMs is not what kills engines if they are built right.

dakfink
09-21-2009, 09:02 AM
T&D rockers and good springs help too. Only thing holding me back now is the fact that it's still a hyd roller, but peak hp is at 63-6400, so I don't need to go much past that anyway.

Actually you don't have to go that far.

A good set of rocker arms and Valve Springs and your good to go.

The engineer that wrote the HOW TO BUILD BIG INCH SMALL BLOCK MOPARS, was also one of the ones that was in on the designing of the Magnum motor.

Here's what he had to say about Magnum engines" The 59* lifter angle isn't optimal for high rpm race motors but should hold up reliably to 7000rpms.

HI-RPMs is anything over 7000rpms.

As for the Hydraulic Roller cam? your fine. We used to run LS-1's all day long to 7000 rpms on a HydRlrCam.

dakfink
09-21-2009, 09:18 AM
408 motor with 456 gears good together or no? maybe stay with 392

To answer you! Yes and No!!!

As was stated, need more info.

Especially what your running now and anything you plan to change to in the future.

MY EXPERIENCE: several years back I was running a Supercharged 408 with 4.56s and even with 31" tire and staying in 3rd (46re with ViperConv @2400 Stall)i would run out of RPMs by 100ft short of the 1/4. That was with a 6000rpms red-line.

What I know now: I would have gotten better Valve Springs and ran it on up to 7000rpms. And probably ran a 28-29 inch tire.

The Magnum motor is not the Lame Duck of the Mopar World than many think it is. It has it's issues in stock trim, and a few people have grenaded them in the past when Proper Tuning wasn't available.

I know KRC is make 450+ rwhp on a 100% stock motor(with Turbo on top), That's easily 500hp at the crank.

A good set of heads, the right cam, Roller Rockers and a good set of Valve Springs and I wouldn't be scared to run a a magnum motor to 7000rpms at all.

If I can ever get the wifey to let me get another Dak (that's 4-letter word at our house) I'm going to build a nasty Monster that will turn 7000rpms on a Magnum Block.

bad360rt
09-21-2009, 09:43 PM
Actually you don't have to go that far.

A good set of rocker arms and Valve Springs and your good to go.

The engineer that wrote the HOW TO BUILD BIG INCH SMALL BLOCK MOPARS, was also one of the ones that was in on the designing of the Magnum motor.

Here's what he had to say about Magnum engines" The 59* lifter angle isn't optimal for high rpm race motors but should hold up reliably to 7000rpms.

HI-RPMs is anything over 7000rpms.

As for the Hydraulic Roller cam? your fine. We used to run LS-1's all day long to 7000 rpms on a HydRlrCam.

Yup, I meant holding me back from going past 7k, I shouldn't have any issues revving it to the high 6k's. :biggthumpup:

Lederip
09-21-2009, 11:56 PM
408 motor with 456 gears good together or no? maybe stay with 392

I would go with the 456 gears and run the diameter tire that gives you the desired rpms. I trap at 6800+ rpms at 127 mph with a 30 inch tire.

slvr03dakrt
09-22-2009, 02:02 AM
I'm still on stock 3.92 gears with a 3500-3600rpm stall that flashes around 4k. It does pretty good but I would benifit with 4.10's if I was spraying it still but I took my kit off on motor 4.56's would be optimal. I really like having my od and 3.92's to freeway cruise at 70mph turning 2100rpm. If I ever re-did the rearend I would put a set of 4.10's in there I just can't justify the step up to 4.56's being that its still an everyday driver.

Intense RT
09-22-2009, 04:42 AM
I'm still on stock 3.92 gears with a 3500-3600rpm stall that flashes around 4k. It does pretty good but I would benifit with 4.10's if I was spraying it still but I took my kit off on motor 4.56's would be optimal. I really like having my od and 3.92's to freeway cruise at 70mph turning 2100rpm. If I ever re-did the rearend I would put a set of 4.10's in there I just can't justify the step up to 4.56's being that its still an everyday driver.

I'm with you on that one. I may go to 4.10's, maybe. Also, wasn't slammedr/t running 3.92's? He movin' right along. I guess he may change them now.

dakfink
09-22-2009, 05:32 AM
I guess you also need to define what is Daily Driving for you???

I used mine as a daily driver when I had 4.56's.

BUT; my daily driving was 6-8 miles to go anywhere, at the most.
Work was 2-3miles, Shopping was 3-4miles.

My biggest journey of the week was the car show on Sat and that was 13-15 miles away.

So 4.56's didn't hurt me much.

Now if your daily routine consist of 20+ miles everyday. I wouldn't do it.

slvr03dakrt
09-22-2009, 06:29 PM
Yea my drive to work is 22miles each way so around 50 miles a day. I normally drive around 300miles a week and sometimes more. I love the ability to hop in my truck and take a 100+mile cruise with no worries. I have no doubt that my motor will turn 3k rpms for miles on end but thats a good bit of extra wear on the internals and valve springs I plan on freshing the motor up around 25k miles or 1.5yrs.

krs1r/t
09-22-2009, 11:41 PM
i dont drive mine i have a slave car

Rtspeeddemon
09-23-2009, 02:53 PM
WHY???

a Magnum Motor will hold a lot more than any of us have throwed at them so far. Especially in N/A trim.



Were testing that theory in 2 weeks. Hope to hit the track Oct 10th during an upcoming event. Although of course not running in NA trim either ;-) Fingers crossed it holds the extra power and stays together. Oh and still running 3.92 gears in mine with 28" slicks.