Gearhead_42
Gearhead_42 Dork
10/14/12 11:26 a.m.

So, hauling (ass) home with my new '74 EMS, I started thinking about optimizing a tow vehicle motor for racecar hauling.

Let's say certain small block Chevy Tahoe turns 2000 to 2200 RPM at typical highway towing speeds. How would I go about choosing ports/cams/fueling to try to keep it in that range? Basically, give it enough oomph to not need to downshift as often into the 3000-3200 RPM range that 3rd gear runs (and the insane fuel consumption that come from TBI at that kind of engine speed)

Thoughts? I'm looking toward doing some mild upgrades to the 350 TBI in there, already have TBI spacers, shorty headers, nice single exit exhaust...

Ranger50
Ranger50 UltraDork
10/14/12 11:57 a.m.

Convert to a 5spd.

But really, increase your low-midrange torque. And fix how that 4L60E shifts.

oldeskewltoy
oldeskewltoy Dork
10/14/12 1:15 p.m.

it really depends on what the current set-up is... you might be able to optimize the ports and make minor improvements, but until you know the current cams duration, and where the current set up makes torque much else is all based on rumor....

To keep your rpm in the low 2000s, a high cylinder pressure would go a long way... that usually means shorter duration camshafts... or at the very least a intake valve closing event nearer to BDC.

Another way of keeping the power on down low.... a supercharger... find a twinscrew that is a good fit to your engine... a supercharger kit might just be cheap enough that cams, head work, and associated parts, along with time and effort might make the S/C cost effective......

Gearheadotaku
Gearheadotaku SuperDork
10/14/12 2:29 p.m.

The down shift takes a lot of load off the 4th gear clutch pack in the trans. If you want to pull that kind of load in O/D, make sure the trans is up to it. You'll spend more in upgrades overall than you'll save in fuel unless you tow alot.

WhiteLX
WhiteLX Reader
10/14/12 2:37 p.m.

Kenne Bell

z31maniac
z31maniac PowerDork
10/14/12 2:47 p.m.

None of this sounds cheaper than buying the extra fuel when towing......

Trans_Maro
Trans_Maro SuperDork
10/14/12 2:57 p.m.

Check to see if Banks makes anything for your truck.

They do gas stuff as well as diesel and their products seem to work well for tow vehicles.

I've driven a couple Banks-equipped trucks and been happy with the results. I'm thinking of using one of their kits on the 460 in my F-250. They make a trans reprogrammer for the E4OD, I'd bet they have one for the 4L60E.

Streetwiseguy
Streetwiseguy SuperDork
10/14/12 3:31 p.m.

Change diff gears so it runs 2500-2800 rpm in 3rd gear, then use overdrive when you are not towing. Your trans will be much happier using a 1:1 ratio under load, and the engine will produce enough torque to keep you going easily.

HappyAndy
HappyAndy Dork
10/14/12 3:36 p.m.

Home brewed turbo system. Set up as light pressure system, max pressure 6 to 8psi, modest intercooler, no boost control other than the pneumatic waste gate. Do your homework to properly size the turbo so that its in its sweet spot at your target rpm. Tune ecm to compliment the turbo. Talk to someone else about what to do with the trans, I'm sure it will need something, but I haven't a clue what, other than cooling.

For the record, my advice is probably worthless. I've never actually done this, but I want to.

Carro Atrezzi
Carro Atrezzi HalfDork
10/14/12 4:00 p.m.
HappyAndy wrote: Home brewed turbo system. Set up as light pressure system, max pressure 6 to 8psi, modest intercooler, no boost control other than the pneumatic waste gate. Do your homework to properly size the turbo so that its in its sweet spot at your target rpm. Tune ecm to compliment the turbo. Talk to someone else about what to do with the trans, I'm sure it will need something, but I haven't a clue what, other than cooling.

then quit your day job and open a performance consulting firm building wicked rides on the side

dj06482
dj06482 HalfDork
10/14/12 8:31 p.m.

Streetwiseguy is right on the money, cheapest is to re-gear and run in 3rd. Given that you're running a TBI Tahoe, towing in OD was not recommended from the factory for the 4L60E (my '94 pickup had a big sticker on the door saying so), so you'll have a good chance of saving a transmission rebuild. A big cooler will also help out to lower transmission temps and extend the life of the transmission.

Sounds like you have a set of 3.73s in there, a 3.42 will likely get you in the right range, but you'll have to check the math...

And one possibly cheaper option is to run a taller tire and tow in 3rd.

81cpcamaro
81cpcamaro Reader
10/14/12 8:40 p.m.

I agree with the others, re-gear to keep it in a better rpm range. My Dakota R/T 5.9L could stay in OD most of the time, but it had 3.92 rear gears. Honestly, after towing my 28 ft enclosed trailer with a 350 SBC in my Dually, a bigger engine is needed to pull better at low rpms (it doesn't have OD, just granny gear 4-spd). Diesels of course do this best, followed by Big Blocks and V10s. The 350 pulls decently but needs to be higher in the rpm range to do the job.

HappyAndy
HappyAndy Dork
10/14/12 8:42 p.m.

In reply to Carro Atrezzi: sarcasm sarcasm?

fidelity101
fidelity101 Reader
10/15/12 7:24 a.m.
Gearhead_42 wrote: So, hauling (ass) home with my new '74 EMS, I started thinking about optimizing a tow vehicle motor for racecar hauling. Let's say certain small block Chevy Tahoe turns 2000 to 2200 RPM at typical highway towing speeds. How would I go about choosing ports/cams/fueling to try to keep it in that range? Basically, give it enough oomph to *not* need to downshift as often into the 3000-3200 RPM range that 3rd gear runs (and the insane fuel consumption that come from TBI at that kind of engine speed) Thoughts? I'm looking toward doing some mild upgrades to the 350 TBI in there, already have TBI spacers, shorty headers, nice single exit exhaust...

Thats the problem with my 3/4 ton suburban, it is manual but its a granny 4 speed and 4.10 gears so even 60mph on the 31" ish tires on it make it scream down the highway... going 60, its about 10mpg maybe less but I just did a tune up on it so I'll have to see if that changes (plugs, cap, rotor, wires)

an RV cam would help, and I would go with long tube headers rather than short tubes but if thats what you got then roll with it lol. I'll have to look up TBI spacers,

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