Subject: P-30/454/TH400 (no lock-up) drivetrain w/ 31" dia tires on a short, 24' coach, primarily running the East Coast flatlands lightly loaded. (i.e.: No need for a hill lugger...)

My shop just informed me of exhaust manifold problems so this might be the time to go the Thorley header route to help with the normal 454 heat dissipation issues.....seems that most people are pleased with a noticeable torque increase.

But in my case, being 24' & light on flat ground, I have had a "surplus" of power all along, even with the cast iron manifolds. (2' shorter Barth model used 350cid) Plus, it seems like engine rpm is much higher than need be at 60mph cruise....No tach yet, so don't know real numbers, but it sounds overly busy down there.

Due to unit's age & modest investment, GearVendors is not an option. But how about the rear end?.......It's currently a 4.56, same as all P-30's in all wheelbases I'm told, so this same 454/TH400/4.56 set-up is designed to routinely handle loads far exceeding mine. (12.3k gvwr)

Crunching rough numbers, (if I did it right), stepping down to a 4.10, or even lower, rear would reduce my cruise rpm's by 300-600 and still be within an acceptable torque band - I think......Ring & pinion swap-outs have been quoted in the $400-500 range, so cost is much less of an issue than a GV overdrive project.

What say ye all?....There must be tons of issues I haven't even thought of yet.........
I don't want to reinvent the wheel, but it sure would be nice to quiet-down the doghouse a little - maybe even bump-up the mpg a tad.....without too much compromise of power.

quote:

Originally posted by Lee:
But how about the rear end?.......It's currently a 4.56, same as all P-30's in all wheelbases I'm told, so this same 454/TH400/4.56 set-up is designed to routinely handle loads far exceeding mine. (12.3k gvwr)

Crunching rough numbers, (if I did it right), stepping down to a 4.10, or even lower, rear would reduce my cruise rpm's by 300-600 and still be within an acceptable torque band - I think......Ring & pinion swap-outs have been quoted in the $400-500 range, so cost is much less of an issue than a GV overdrive project.

What say ye all?....There must be tons of issues I haven't even thought of yet.........
I don't want to reinvent the wheel, but it sure would be nice to quiet-down the doghouse a little - maybe even bump-up the mpg a tad.....without too much compromise of power.

I think we would need a tach reading to make a correct decision here. My gut feeling is to go Thorleys and 4.10. Can you do rear end set up yourself? That is a significant saving.

Whaz wrong wih your cast manifolds? You can have my 454 cast manifolds for just my discounted cost of shipping. I replaced them to put on Thorleys, and they seemed not to leak, but having them surfaced would be worth it.

There are only two problems I see.

First thing is change the P-30 comment to P-32 before someone else see's it.

Second thing would be a replacement speedo drive or a speedometer cable adapter.

Other then that I see no reason why you shouldn't do it.

The motor will last longer. The engine heat should be less. The mileage should go up. The noise level will go down. Less wear and tear on alternator, water pump and anything else being driven by the engine.

No Gear Vendor and the added cost of such a unit. You seem to be on track with this.

Based upon the torque, weight, and your use the 4.10 sounds like the way to go. The 4.56 is just to much gear.

Opinion: The 4:10 rear - Yes. Headers? Maybe. With the lower-RPM cruise the headers are perhaps redundant.

Save more money and pay the freight for Bill H's manifolds. Headers, while benificial, might just be a little redundant after all. It wouldn't hurt, but there's not that much more bang for the buck.

On my P series 27 foot Rockwood I had 4.1 gears with the 4L80E trans which does have overdrive, I would run about 3000 RPM at 70 in 3rd and about 2200 in 4th (OD) Check what you have first, 4.56 sounds short for the big block application. I had Banks headers and it DID make a LOT more torque, I also made heat tunnels for the long headers to run thru so that the heat would be separted from the trans area.

HTH

Lee:
According to my 1983 Truck Data Book, there were
two axle ratios available with the 12,300 GVWR
chassis; a 4.10 RPO GQ1(Non-locking diff.) and
a 4.56 RPO HC4(Locking diff.). Do you have 7.50-16/D tires? I can mail copies of the Motorhome
section of my 1983 Truck Data Book, if they can
scan them into PDF form and put them in the Forum. I believe that Dave can. I need to check
Product Information at the GM Tech Center to get
copies of other years.

Jake Jacobson

I will agree somewhat with headers being of limited usefulness at cruise. I have put headers on almost all my vehicles for decades, usually Tri-Wye, and the benefit is most apparent when the pedal is down. Even more so when the revs climb. And even more so yet up hills. There is a little better throttle response with light throttle, but in a heavy vehicle, that alone is not worth the cost. If I never saw another steep hill, headers would not be worth it to me.

However, when hills must be climbed, headers are well worth it to me.

I have a friend in Colorado who is on the same page is me regarding MH performance. He has the advantage of living near a 6% half-mile hill at 7000 ft with little traffic , so he can do better testing than I. He is very knowledgeable and experienced, so I respect his results and opinions 100%. He has a 1988 32' SOB on GM PEE-something Chassis.

Here are his results with cold air and Thorley headers:

Test Conditions: Hill climb, paved road, 7000' Elevation, 6% grade, .5 miles

Test Technique: Start hill @ 50 MPH, full throttle and manually shift for best speed

Metric: Speed at top of hill

Stage1: All stock, new plugs, wires, carb adjustment etc.

Stage1 Result: 43 MPH 2nd gear, speed still falling


Stage2: Added self fabricated air scoop*, 2.5" dual exhaust w/HP mufflers, cross-over-pipe
Stage 2 Result: 48 MPH in 3rd gear, speed still falling


Stage3: Added Doug Thorley Headers

Stage3 Result: 53 MPH in 3rd gear, speed holding steady
Note: Stage3 allowed acceleration up the hill

Notice that all of this is in Third gear, so the Thorleys are of considerable benefit in the 2300-2500 rpm range, which is below normal cruise.

He did his exhaust before either one of us had investigated X pipes, and we both agree that an X pipe would be worth trying.

Our experience with other vehicles leads us both to believe that the improvement in performance would be even greater at lower elevations.

quote:

Originally posted by Lee:
primarily running the East Coast flatlands lightly loaded.(i.e.: No need for a hill lugger...)

But in my case, being 24' & light on flat ground, I have had a "surplus" of power all along, even with the cast iron manifolds.

Due to unit's age & modest investment, GearVendors is not an option. But how about the rear end

it sure would be nice to quiet-down the doghouse a little - maybe even bump-up the mpg a tad

So, it seems like we all agree. Headers (for him) would be of limited use.

He just wants to save some money and at the same time lower the RPM and fix the exhaust. I agree with the post that headers would help, but based upon what he wants to do with it, it sounds like he will spend more for having headers without the benifit of gearing.

While those mods would help performance it will make the mileage suffer if he spent a lot of money on headers and nothing on the rear. Saving money first on the rear setup while getting Bill H's exhaust manifold will buy him time and allow for a real world test on power, mileage and sound levels.

If after driving it he may realize he needs more performance he can always revist the header issue. He could add a fresh air scoop and exhaust crossovers too but he would need to check if this rear mod is "good enough" for his use. I think he should have enough power and would be fine with just a tune-up and the rear end mod. If he wants to get creative he can hand make a cold air induction for pennies on the dollar, that will save some money and increase performance too.

Yeah, especially on a shorter Barth.

Headers usually increase mileage a little, but that is often mitigated by the driver using that extra power the headers gave him. Claims by manufacturers seem to be a little optimistic, to say the least.

I should add that cold air induction can also improve fuel consumption. In my own case, towing, weight of boat or toad, not towing, hills, mountains etc make each tankful different, so I can't document it accurately

Wow!...Tons of info & insight!...Thanks to everyone who weighed in.....What a GREAT site!

Based on feedback, I'm deducing that:

1. Size/weight/terrain/available torque makes a swap-out from a 4.56 to 4.10 rear a possibility to lower rpm/noise/fuel consumption.

2. Header install may (or may not) be necessary to reclaim any lost torque from the change in gear ratio.

The suggestion to swap-out gears and then wait-n-see regarding power needs is a good one. My original thinking was that headers, combined with the new gearing, would give me a strong 55mph second gear for the occasional jaunt to the mountains....a nice-to-have, but certainly not a have-to-have....

The existing manifolds are still useable....it's just that a quick-n-dirty Zyglo inspection indicated several unseen cracks radiating out from the mounting flange areas. (The previous owner's logs indicate manifold replacements at about 45k miles - makes me suspicious of possible over-torque when they were installed.) Anyway, I've got the ability to run with manifolds and the new gearing to see if additional power is indeed needed. If so, Thorleys would seem to be the next logical step. (Sidebar: My nephew built up a 454 SUV rock-climber, complete with ported & polished intake manifold...If past-is-prologue, he'll wreck it any day now, and I'll have an easier breathing intake manifold for pennies on the dollar to go along with the headers.)

Cold air induction is already a done-deal - 6" piping from just behind the grille.

NOW, here's where I get myself really confused on drivetrain theory and could use some thoughts: It seems to me that the added "rolling resistance" of the 4.10 rear translates into additional work (& heat) at the torque converter - I don't "think" a gear change can be a zero-sum game.... If so, is it enough that I should be considering additional cooling for the tranny fluid? Right now, it's got the OEM cooling lines in the main radiator, in addition to a Derale deep tranny pan with the fluted cooling tubes running through the bottom. The soon-to-be-installed tranny temp gauge will answer this questiuon, but if it's already a no-brainer I'd like to install a Hayden aux cooler while the coach is still down.

Lookin' forward to your thoughts,....again!

"...added "rolling resistance" of the 4.10 rear translates into additional work (& heat) at the torque converter - I don't "think" a gear change can be a zero-sum game....".

I am not knowledgeable but IMHO: The 4:10 is in effect an overdrive, thus runs cooler at cruise (???). Start>acceleration to cruise speed - yes, more work and heat, but it seems logical that at warp speed less heat/strain in the gears. What do our leftcoast hotrodders think?

How much is the rear end change going to cost? Have you projected savings in fuel and engine life? I had to address these issues before buying a Gear Vendors overdrive. I decided that the saving was not worth it. But I would feel more fulfilled as an individual and a fiddler if I went ahead and did it. You know, boys and their toys.

Sometimes logic and numbers are not the whole story, even if they should be.

You will definitely lose torque and throttle response in third with a higher ratio diff. The issue is really, how it will affect you. You have a big engine and a light coach, so, on flat, it is a good thing. In mountains, you will have less third gear climbing ability but will have gained the ability to use second gear at higher speeds. Trade off.

Do you tow in mountains? That is where you will be hurt the most.

Is the intake in question a Performer? They are good. I have one I am going to install some day.

Are you using synthetic trans fluid? That alone may be enough. It is not a big deal to put on a trans cooler after the other work is done. Since you have a gage, I would wait and see. My own experience is that my worst tranny heating is fighting my way into boondock parking in the mountains where a lot of maneuvering back and forth is required. That is to say, high torque requirements and low air flow. Stop and go traffic on a hot day, too. To be safe, an add on tranny cooler is always a good idea, though. As you climb a mountain and the tranny temp keeps slowly rising, there is always a temptation to chance it and keep going instead of stopping to cool it down. An added cooler would avoid that situation. Since your high gear climbing will be impaired, you will be doing more climbing in second, which is usually a little easier on the tranny.

I have a 454 truck, and tow a heavy boat with it. It has an overdrive that, I believe is 70%. It climbs pretty well in OD. Your proposed gear change is the equivalent of a 90% OD. That is not a giant difference.

Sitting here in my chair, since I do a lot of mountain driving, I would not do it, especially with a toad. If I had experience driving your coach, I might have a more informed opinion, however.

Still sitting in my chair, if I did mostly flat driving, I would probably do it. Even if you tow, you will be OK on the flat.

Something else-since you will be "lugging" the engine a bit more, you might need premium fuel or a timing readjustment, depending how it is set now. Retarding the spark may cause the engine to run hotter. You might need to shut off the dash air before climbing to reduce the cooling load both on the engine and trans.

quote:

Originally posted by Gunner:
What do our leftcoast hotrodders think?

= Really confused?

quote:

Originally posted by Lee:
Wow!...Tons of info & insight!...Thanks to everyone who weighed in.....What a GREAT site!

NOW, here's where I get myself really confused on drivetrain theory and could use some thoughts: It seems to me that the added "rolling resistance" of the 4.10 rear translates into additional work (& heat) at the torque converter - I don't "think" a gear change can be a zero-sum game.... If so, is it enough that I should be considering additional cooling for the tranny fluid? Right now, it's got the OEM cooling lines in the main radiator, in addition to a Derale deep tranny pan with the fluted cooling tubes running through the bottom. The soon-to-be-installed tranny temp gauge will answer this questiuon, but if it's already a no-brainer I'd like to install a Hayden aux cooler while the coach is still down.

While the addition of better highway cruising gears will in fact cause a very slight increase in temp and just a little more work at the torque converter. Only at start up, heavy city driving, a long nasty hill and a brutal headwind. The temp aspect is really not a factor. It really is, as you say, a no-brainer.

Any transmission will benefit from better lines and larger coolers. You should consider this a cost saving addition to the overall life of your transmission.

When I say that the temp really isn't a factor we are still going by your variables that were first posted. Now if you had some type of rock climber and you were always off road or are driving this in a city all of the time, then this issue would be of a some (little) concern.

You own a motorhome and the thought of a rear end gear swap out causing any "real problems" is just your mind telling you that there's something more. Can it really be that simple?

Yes it can. You should go to sleep tonight telling yourself that you came up with a great idea and without the cost of the gear vendor!

Now, if you decide to gut the interior, load freezers onto it and sell hotdogs out of it to the city folks then leave the rear alone.

As you pointed out: If this coach was 2' shorter it would have a 350 in it should tell you all you need to know. You will have plenty of power with only marginal loss of hill climbing ability. You won't win off of the line at a stop light but your not racing 1/4 mile either.

Looking forward to your post after you do your mods. Can't wait, as real world will tell you more and make you a very "happy camper."

---

The approximate life expectancy at various temperatures is as follows:

175°F - 100,000 miles optimum street temps
195°F - 50,000 miles max street temps
212°F - 25,000 miles fluid fatigue
235°F - 12,000 miles varnish forms
255°F - 6,250 miles seals start to harden
275°F - 3,000 miles
295°F - 1,500 miles plates start to slip
315°F - 750 miles seals and clutches burn out. Oil forms carbon
335°F - 325 miles
355°F - 160 miles
375°F - 80 miles
390°F - 40 miles
415°F - Less than 30 minutes

Above 295°F, the metals inside the transmission will warp and distort. This is why rocking in snow, mud, sand etc. should not exceed a few minutes.

On the subject of cast manifolds........ Are the cracks on just the right side or both?

Cut a slot between each cylinder with a hacksaw or cutting wheel. Have a machine shop surface grind the manifold. Drill the bolt holes oversize and spot face the washer surfaces, use new Chevrolet bolts and Unbrako washers. Use red silicone rubber as a gasket. Torque to 40 ft lbs in 10 lb increments from the inside out. Use an anti seize on the threads. Retorque on a hot engine after one trip. Chevrolet does not use a gasket, however many experienced mechanics have varying opinions on the gasket issue.

After all that, it will warp again, but not too soon. Install a right side splash shield to improve right side cooling. Avoid heat soak by idling for a little while before shut down after a hot run. Or better yet, have a thermostat controlled electric puller fan that runs for 5 or ten minutes after shut down. The fan will also avoid heat soak damage to wiring and the starter solenoid