The Stovebolt Site Forums The Shop Area Engine Shop Tuning with taller R&P in a 235

Hi guys.. I started a thread a while back about ring and pinion options for my 62 c10 with a 235 one barrel carburetor and a SM420 rock crusher transmission..
Anyway, I ended up bolting up the entire rear end from a 69 that had a 3.07 R&P already in it.. When I bought the truck it had a 4.10 in it. What a difference..!!
I have to say that the experiment was very fruitful.. The truck seems to be running right where it needs to be for my application.. The rpm's are staying right between 1600-2300 through all the gear changes but start pushing up past 2500 as I climb past 65mph.. I could get a taller tire and lower the rpm's even more.. The truck does not seem to be lugging..
Anyway, now that I have the new drive train I'm wondering if there are any special considerations for the vacuum advance or other items? What I'm shooting for is optimal performance and gas mileage.. I've been reading some threads and I have heard mentioned that maybe these are things I have to reconsider now that I've changed the drive train..?

There's nothing new to consider due to your gear change...the tuning should be the same. You're more likely in a useable powerband with your new gears. These old trucks were not intended for today's freeway speeds, they were meant for hauling hay around the farm. There's generally a lot of potential for tuning if you enjoy it, otherwise run it as it is.

I tune race cars on the side, and have applied the same things to my truck to some degree. It was getting 12 mpg, now I'm up to 20 and still tinkering with it. I have the same 235/ 1bbl combo you do, but I have 3.55 gears.

Devin

Devin,
Dam..!! I'd love to be getting 20 mpg outta my 235.. I don't think i'm quiet there yet. I still have to recalibrate my odometer and speedometer.. I'm going approximately 10 mph faster than what my speedo is telling me currently.. So I know the odometer is way off as well.. But near as I can tell, I'm getting between 11-13 mpg now.. Maybe that will prove different after I do the re-calibrating?
What else can I do to get up to 20 mpg with this shoebox? I am in the process of getting rid of the stock muffler on there.. It has a fold in it so I know it is restricting the exhaust big time which also has to be killing my mileage.. Was gonna throw a 1 3/4 glass pipe on there..
Any suggestions you can give me to get it like yours i'm down for experimenting.. I put the magnetic ignition and flame thrower in.. Got a new remanufactured Rochester one barrell and an entire new head as well.. Running 27" tall tires with the 3.07 R&P..

With the low compression of the 235, try turning the timming up a bit. I would keep going till I heard some pinging or it started to run bad, then back it down some. Set the idle mixture screw in a bit, it saves fuel if on the lean side, and lower the float a bit. It all adds up, but takes some time and a lot of drive time to get there. Joe

I put a taller gear in my 37 and the gas mileage got worse,I also had a weak fuel pump and was in the gas more then usual to keep it going which could of been opening the power valve causing the drop in gas mileage but I have not driven it too far since the pump replacememnt to see if mileage improved. I got 2.79 gears in it and its a totally different truck and its quick off the line but I might be straining it a little. Jeff

Richie- I'm running a 3.55 rear, but I have 30x9.50 tires on the back, so our rpms are probably similar. I've played significantly with the timing, both total and initial, as well as the curve. It's been a while since I got it set, but I want to say initial is 15 degrees and total is 41. Any more than 15 initial and it didn't want to crank, more than 41 total and it would ping. Total timing in by 3000 rpm. I am still running points, so plug gap is set at .035. I would go up to .055 or so if I had electronic ignition. I run Autolite 45 plugs. If I did more highway driving I would go to 44s, or 43s if I could find them. As for the carb, I hooled my oxygen sensor to it for a precise reading, but you can get close the old fashioned way. with it fully warmed up, set the mixture screw to the highest idle speed or vacuum, either will do, then go in about 1/4 turn. I found my carb was jetted way fat, I was at 11.4:1 air fuel ratio when on the main jet, anything above 1500 rpm or so. I measured it with a drill bit, I think it was .058", then soldered it closed and drilled it out to .041 I believe. It took several tries to get it close to 14.7:1. Carbs don't run as precise as fuel injection, so it honestly runs between 14.5 and 15.3:1. Mine stumbles a bit on acceleration because my accelerator pump isn't working, so it causes me to drive like a grandma, but I'm ok with that in an old truck. I'll fix the pump someday.

Don't take any of my settings verbatim, it's been trial and error to get here, and may not work for your truck. I have probably 20 hours of tinkering and thousands of dollars in tools to get here. Find out what your engine likes and it will reward you.

Devin

Cool stuff for sure.. I think for [censored] I'm gonna throw a new fuel pump in for starters.. Thanks Devin and all for the tips.. I want to print out this page and hand it to my mechanic.. I also think the new exhaust system will help once I get that installed.. Going to go through all of these suggestions one at a time..
Thanks, will keep you posted of my results..

Devin, thats pretty cool how you got where you are. It sounds like what I have done over the years. I use a hand held exhaust sniffer stuck in the tail pipe. My engine with three small (70 cfm each) carbs runs in the high 14.7 to 15.0 range. It stumbles a bit to, but thats just if I floor it or really step hard. Since I only have to step down a little to really get going, the pumps don't have time to do much. One of these days I will change the leverage on them so they work better with less movement. I can't tell you how many times I have had these carbs apart, I've even got some solder up and drilled out ones myself. I have to admit, this is the stuff I really like, making it run as best as I can with what I have. I hate to see stuff done half way.

I can get in the 17 mpg range with a 3.08 gear, 27" tire and automatic trans., but thats mostly at 70 mph. It really helps to slow down, this '37 pushes a ton of air with its flat windshield!

Joe

Thanks for the kudos guys. As I said in my first post, i do this on the side for race engines. I have taken BB cars that were getting 8 mpg up to the high teens. It can be done with any vehicle that is adjustable, just takes some time. My daily driver 63 Corvair gets 34 mpg from the same kind of work. It was getting 20-22 when I started.

Devin

One more question.. I've heard that you can actually buy different size jets for these Rochester one barrels.. I guess they supposedly use to put different jets in them accounting for where it was being sold and where it would be running.. Meaning different temperatures and altitudes in various parts of the country.. It makes sense to me but I don't know how true it actually is.. Just a had a mechanic friend of mine mention it to me..
Anyway, my question is that if i shrink the jet hole thereby decreasing the amount of gas being sucked into the intake, wouldn't that put me at risk for running the engine a bit hotter than it should be? I guess I would have to [censored] with the air/fuel mixture until it came to a amiable setting?
Also, as a matter of interest, I am currently running 225/75R15's on my wheels.. I took a tape measure and measured from the ground to the top of the tire and it read 27" in height.. I was told those tires were 25" in height.. Is that what the call it but actually is something else? Or did I just get bad information?

Richie- In regard to your jets, I was not able to fine any replacements in any size for mine, which is why I soldered them closed and drilled them out to a smaller size. I doubt that you'd find them as small as you'd need to be efficient if you did find them.

The engine will not heat up unless you run it TOO lean, above 16:1 or better.

Your tires are what they measure, regardless of specs. I have a set of those on my El Camino and they are about 27" also.

Devin

Thanks Devin.. I have and extra carb that was rebuilt.. I had it on there for a while but just went ahead and ordered a new one.. I actually got worse gas mileage when I put the new one on.. About 1-2 miles less.. Anyway, point is I have an extra jet to experiment with.. A good mechanic friend of mine that works on old cars suggested I do that long before I ever joined Stove Bolt.. Turns out I ran into him today and he's down for taking my old carb and redoing the jet..
I don't have an oxygen sensor nor does he.. But he suggested I buy one or we can try it the old fashion way? They are just over a hundred bucks.. Not sure I wanna spend the money on it if we can get away with doing it old school..
I actually looked at my spare tire closely today.. Turns out it's an old school bias ply tire. Man does it look cool.. But obviously not gonna be what I end up running on there..

Richie- I don't know what kind of oxygen sensor you found for a hundred bucks, but if it's not a wide band it's not worth buying. I got my setup from Innovate Motorsports....www.innovatemotorsports.com

It can be done the old fashioned way by constantly checking the plugs after each change. My expereince with these Rochester 1BBLs has been that they can be decreased in size to approximately 2/3 to 3/4 of original. Take it gradually though, because if you go too far you can put holes in your pistons.

Devin

Thanks Devin, I will look at that link.. Not sure what you mean by burning holes in my pistons but it sound squary..!! Or scary depending how old the person is your talking to.. Me, I'm like a 5 year old when it comes to the bolting stuff.. Learning as I go from guys like you and my mechanic friends.. So Squary applies to me..

richie- You have to understand here, as I'm a really sick individual, I work on cars for a living since i enjoy them so much. Then I come home on nights and weekends and play with them more. I have to deal with late models and fuel injection and stochiometricity on a daily basis. These old rigs were not meant to be efficient, merely to get a job done. There was lots of slop by today's standards. I improve the efficiency as much as I can, but truth is, these things are as aerodynamic as your average brick, so there comes a point where no more can be done. I hope I've been some inspiration as to what can be done, but as I said earlier, it is time consuming and expensive if you're paying somebody to do it.

Devin

Agreed Devin.. I know one thing for sure.. Something has to be done about my current fuel consumption.. I have a 3.9 liter motor with a one barrel carburetor and a 3.07 R&P and I get 10 mpg..
My friend has a 5.2 liter motor with a 4 barrel carburetor and a 3.90 R&P and he's getting 10 mpg.. So obviously something isn't right..
I am going to replace all the gas lines and connectors and the fuel pump.. (maybe they are leaking?) and re-jet the carburetor and replace the exhaust system with a glass pack..
Beyond that I don't know what else to do..

Richie,

Gas milage has alot to do with driving style. Drive easy with a light foot and keep your speed down and you will get better milage. Drive with a heavy foot and fast will not be good on the pocket book.

Thanks Lonnie Gallaher.. I drive like an old lady, no joke.. the guy that I was talking to that has that 5.2 liter with the 4 barrel carb told me he gets ten mpg wether he's got his foot to the floor all the time or wether he drives it slow.. And he's only one guy I know out of dozen that have similar set ups and are getting between 8-10 mpg..
I'm just say'n that the math doesn't add up comparatively with my set up.. I should be doing way better on gas than those guys.. But I'm doing the same or worse.. So something has to be wrong..