Help choosing gears!

[35Remmy]

Hey guys, I am getting ready to regear my Dana 35 and 8.8 for 35" tires. Truck is an 88 and am almost done building a 302 that will push around 350 hp. This truck is mostly for show except for the occasional logging trail.

My main concern is this: with that amount of horsepower, would 4.88's be WAY too much gear for the strength of the driveline? I will be having much stronger driveshafts made and running stronger axles out back. But that's it. Would I be better off gearing to 4.56? With that much power I dont "think" I need 4.88s but not sure.

I will be purchasing the gears from Jim but didn't want to bother him before asking everyone here first.

 

[don4331]

35Remmy:

I was going to respond to your 7.5 to 8.8 question but as you have opened new thread I don't need to preform thread nemocracy.

From that thread 302 with 350 rwhp:

Assumptions: 302 is naturally aspirated
Engine runs on pump gas
15% driveline losses (SWAG, probably low for C4 as it doesn't have a lock up torque converter).

With above assumptions; Torque will be ~1 ft/lb per in^3. Therefore 300ft.lbs more/less for 302. hp * 5252 / torque = rpm; 350 * 1.15 * 5252 / 300 = 7,000rpm!

Given your 302 is making its 350 rwhp @ 7k rpm; torque peak will be over 5k rpm. (torque peak usually runs ~70-75% of power peak - new engines with their sophisticated controls can move this; but for Windsor, it will be ball park).

Given the above: 4.88s should be considered minimum; 5.13 would be better.

If one of my assumptions is off (HP isn't has high/racing gas + higher compression/forced induction/etc); my recommendation is not longer valid.

 

[35Remmy]

Don, that was one hell of a response and it was much appreciated!!!

I guess I am understanding this backwards? I "thought" with more horsepower/torque it took less gearing to get things moving so to speak. I was thinking that torque would be multiplied at a much higher rate with more hp and torque combined with a lower gear ratio.

Or are you looking more or less a where the usable torque will be within the powerband? Again, thanks a ton for your help. Couldn't do a lot of this stuff without you guys.

 

[bobbywalter]

350 hp 302?


what style exhaust? a good x pipe or two into one with a 3 or 3.5 single out and decent headers will help the low end a bit.


the big question is what trans?


with your 302 at 350 hp putting it at the tippy top of the mild build into hp territory and 35 inch tires, 410 gears would be ideal with a overdrive trans of manual or aod type.

and for sure no lower then 410 with a c4 or c6.


488 gears or lower will suck donkey ass for driving on the highway. unlless you have some sort of non truck ridiculous 8000 rpm cam or something.

i would assume your cam is biased to the goal of a 4x4 and 35 in tires.

 

[don4331]

35Remmy:

I am looking at where your usable power will be:

HP is all about rpm (in absence of forced induction); in order get get big HP numbers; you need lots of RPMs. To get lots of RPMs, you need big induction/exhaust/cam. (Putting a restrictive exhaust on to improve low end, kills HP numbers). Unfortunately, big cam actually pushes air out of cylinders at low rpm. So, at low rpm, torque is lousy = power lousy (as it is function of torque and rpms)= poor drive ability.

If this is going to be a show/mudder truck, no problem; daily driver - not so much fun...

My truck as delivered from Ford:

31x10.5R15; 4.10s; 5R55E trans (0.75:1 o.d.), 4.0 = 1950 rpm at 60mph; torque peak of 4.0 is 2,400rpm, so I have ~80% available at hi-way speed (~180 ftlb). It will kick down to 3rd to pass; putting me @ 3,800, very close to power peak (4,250 rpm on the 4.0) - technically, it gets to power peak as I pass 65mph.

Your proposal. (tires are a guess)

35x12.5R15; 4.10s; C4 trans (1:1) = 2450 rpm at 60mph; as you are only at <50% of peak torque; your 302 actual has less torque (~150ft lbs) than the 4.0. (The truck will feel like a dog).

You actually need the 5.14s to have more torque at 60mph... Now driving 60mph with 5.14s means the engine is running almost 3,100 rpm... Not good for gas mileage.

There's a couple individuals who put "built" Mustang engines in their trucks and were extremely disappointed (no power in od, terrible gas mileage in drive, etc).

If you instead build an engine which makes power at lower rpm (say 250 engine hp @ 5k); then 4.10s would be match. If you want 350hp add a nice blower.

Note: My '82 5.0 Mustang had 350hp/302 engine/4.10 gears and 25" tall tires; and the gears weren't deep enough for best performance...

 

[Dune Runner]

All depends on where this truck will be driven. All trail no street? Mostly street?

 

[35Remmy]

I appreciate everyone's time...to answer everyone at once:

Am running James Duff long tube headers.
Broader Performance 500 HP street/strip C4 transmission
Will be having a CUSTOM cam ground by Ed Curtis of Flowtech Induction, this guy is apparently the cam wizard.
35x12.5x15 BFG M/T KM2
15x10 wheels
James Duff Stage 3 suspension lift
2" blocks out back ( she was originally an STX Hi-Rider, the blocks are from that lift).
2" coil spacers up front
2" body lift
Advance Adapters C4 to BW 1350 to keep her 4wd
Warn Jeep hubs
This was my first vehicle my old man bought me back in the day. She is in nearly mint condition and this build is purely for sentimental reasons.
This truck will mostly be driven on the street/some highway 98% of the time.

 

[35Remmy]

Also,did not mention torque converter. Same guys that built the C4 will be building the converter but they want my cam numbers first.

 

[bobbywalter]

35Remmy:

I am looking at where your usable power will be:

HP is all about rpm (in absence of forced induction); in order get get big HP numbers; you need lots of RPMs. To get lots of RPMs, you need big induction/exhaust/cam. (Putting a restrictive exhaust on to improve low end, kills HP numbers). Unfortunately, big cam actually pushes air out of cylinders at low rpm. So, at low rpm, torque is lousy = power lousy (as it is function of torque and rpms)= poor drive ability.

If this is going to be a show/mudder truck, no problem; daily driver - not so much fun...

My truck as delivered from Ford:

31x10.5R15; 4.10s; 5R55E trans (0.75:1 o.d.), 4.0 = 1950 rpm at 60mph; torque peak of 4.0 is 2,400rpm, so I have ~80% available at hi-way speed (~180 ftlb). It will kick down to 3rd to pass; putting me @ 3,800, very close to power peak (4,250 rpm on the 4.0) - technically, it gets to power peak as I pass 65mph.

Your proposal. (tires are a guess)

35x12.5R15; 4.10s; C4 trans (1:1 o.d.) = 2450 rpm at 60mph; as you are only at <50% of peak torque; your 302 actual has less torque (~150ft lbs) than the 4.0. (The truck will feel like a dog).

You actually need the 5.14s to have more torque at 60mph... Now driving 60mph with 5.14s means the engine is running almost 3,100 rpm... Not good for gas mileage.

There's a couple individuals who put "built" Mustang engines in their trucks and were extremely disappointed (no power in od, terrible gas mileage in drive, etc).

If you instead build an engine which makes power at lower rpm (say 250 engine hp @ 5k); then 4.10s would be match. If you want 350hp add a nice blower.

Note: My '82 5.0 Mustang had 350hp/302 engine/4.10 gears and 25" tall tires; and the gears weren't deep enough for best performance...

hmmmmmm... you know, i totally agree and understand what your saying. its real easy to fawk up a 302/3xx stroker build. REAL EASY.

fortunately for this guy.......the cam and converter are not built yet.....when the intended use is indicated to the cam guy and the torque converter guy, that it will run the vast majority on the street, with 35 inch tires, and only 3 gears....... i cant see anything past 410 gears being ideal with long tube headers. because they are not going to run the power range at 7000 rpm.

that would be patently retarded.

your analogy of your stang with 410 gears and not seeming to be enough tells me allot though. i know i can build a 302 that will blow the tires off of a 25 inch tire car at 80 mph with 323 gears.....and an auto. if that little car needed more gear your setup was miles away. just like the guys that drop "built stang motors" in their 4x4 trucks...you have to cam it accordingly.

i cant tell you how many times guys put shit together and trying to tune it i would end up helping and tear into it and have to change the pushrods and actually degree the cam ect.....and get the 70 hp they were missing....so its real tough to help diagnose stuff on the web unless its and oem platform....and the gearing you suggest would fit that bill.


one version of one of my 302's run close to 330 hp with a custom roller cam and with 30 pound injectors made more torque at 1400 rpm then any oem 4.0 and maintained the minimum of 260 pounds from 22xx to just short of 6000 rpm....i know thats not ideal power as the peak was 3600 ish iirc....running a adjustable timing set...which i suggest strongly for anyone to use on any sbf these days really shows whats out there.

proper sized exhaust and camshaft are uber critical with this motor. 2 degrees on the same cam can make all the difference from a streetable setup verse a slug....all things being equal. from there compression ratio to the cam specifics also holds some keys that are big. but these little guys are easy to work on and fun to play with to some ends....


but this finicky nature with decent low end and the 302, leaves me to suggest starting with a 351 or ls engine these days when running 35 in tires....and the ls will like the 456 gears. but he is not starting with a wheezer pos f-150 or t-bird or crown vic 302....he is starting with a decent build and heads where the cam can be dialed in to suit this requirement.

i personally have been disappointed by the 302 in reg and ext cab 4x4 35 in tire trucks....with a stockish gt40 base it needed 456 gears....with the addition of a truck cam it would lug down almost to 1000 rpm before it would buck overdrive which was cool but useless on the road and to make it worse it fell on its face before 5 grand..hell compared to that i liked the alphabet cams better....you know trying to stay within the stock efi limitations to avoid tuning costs...its what we did thru the 90's..but then tweecer came along.

..with a properly selected cam it ran much better and was able to use 410 gears as well. this made cruising 80 mph a joyful activity. it also allowed 33 in tires for certain long range situations...due to the miles driven its a more cost effective tire. but my truck was always laden during that period as well....i guess if it was just a toy or used empty for basic transportation i could have gone a different route.


513 is too far....456 is tolerable....but with 3 gears i still am on the 4.1 line....i mean at 60 mph your looking at 2400 rpm which should be perfect and you will wish you had gone with a built aod if you will spend time at 70-80 mph. 5.13 gears.....thats like 3 grand at 60 and 3500 at 70......


3 grand at 60 sux...3 grand at 80 dont bug me at all.

but thats me.

 

[don4331]

What compression?

Transmission guys want your cam numbers so the can match the torque converter stall to the rpm range of engine - they should be wanting vehicle weight,gearing/tires and driving style too.

Back in the day B&M recommended the stall speed should be rated at about 500-750 RPM under your engine's peak torque RPM; and to keep it less than 3k for street. I'll be interested in what Broader Performance recommends.

Make sure you have a good cooler as high stall converters generate a lot of extra heat.

 

[35Remmy]

You guys offer more information than I could ever hope for heh. Bobby that's why I know I can't just stick an alphabet cam in there and cross my fingers and hope for the best. For 100$ more I can have a cam ground exactly for what I'm running.

It's also refreshing to hear I may be able to run 4.10's as my rear is already 4.10 and I would just have to change the front which is currently 3.73. That would save cash for elsewhere in the project. I also don't want to be running 3G at 60 mph. That would just be ridiculous.

I didn't know my choice would be so difficult until now and after talking to you guys. Honestly, I still have machine work to get done before I can call Ed and have him work his magic. My cylinder heads are AFF 165s that I purchased off of Corral.net and they had some work done to them and I don't know what they flow or what type of springs they're running or if they've had valve work done to them etc etc. Bought them on a whim for a great price. That being said I also don't know what my compression ratio will end up being.

So I guess from here I need to get this stuff checked out before the cam can be ground and before the converter can be built. I will keep everyone posted and I can't emphasize how much of a help everyone on this site consistently is. Just want to make sure I take this step by step and make sure the right choices are made the first time around.

Can you guys recommend a spot to mount the trans cooler? I just bought an all aluminum V8 ranger conversion radiator for an auto tranny but also wanted to add an external cooler for added insurance. Things will already be super tight up front. I'm not even sure if I'll be able to run a mechanical fan yet.

 

[don4331]

35Remmy:

I run the stock external cooler in its OEM location in front of the rad; and a twin sister right beside it on my '98.

Just to illustrate how little change makes big difference; going from flat-top (-4ccs after valve notch) to small dome (8ccs) changes CR from 9.65:1 to 11.27:1 (assuming 58cc heads per Probe's catalog)

p.s. 'Best' performance in my Stang was defined as lowest 1/4 mile et. And it was done in '86 with medieval parts like a flat tappet cam and 351C 2V heads

 

[35Remmy]

Don it's almost not even believable the difference it can make. I know these AFRs are 60cc based on the part number 1472. But that's it.

Emailed Broader this morning to explain my dilemma and see what they say as far as their recommendation with their c4 and converter. We'll see. I need to just get this damn engine back to the machine shop. I bet I'll have 12k easy into this truck before all is said and done! Damn.