360 fuel consumption - considering reverting to stock cam?

[David Womby]

As I have posted in previous threads, I get pretty poor fuel consumption and a Muscle Car sounding idle. The idle would be great on the right car but not really suited to mine. My Bristol 408 had its engine replaced with one rebuilt in 1991 that I have the following info. for. I know it used .030" oversize pistons so it must now have slightly more than 360 Cu In. The transmission is a 1962 push-button 727 and the final drive is 3.31:1.

1978 Monaco 360 engine.
Mopar Performance Cam 4452761.
Mopar Performance Intake Manifold P4529116.
Piston rings 4.030"
Pistons unknown
Springs 998?​

I am attaching a pic the specs I can find comparing the cam that is fitted and the stock 1978 Monaco 360 cam.

I think swapping my cam for a stock one is just about within my abilities but, before I try it, I expect a stock cam would reduce the idle noise and loping but would it also help fuel consumption to any significant degree?

I also wonder if any other type of carburetor (it has a relatively new Summit Racing Carb SUM-M08600VS. 600cfm) would help? Any advice or opinions would be appreciated.

David

 

[wagonman]

Get an AFR setup and see where the fuel is going.

 

[Photon440]

I would guess that yes, you'll have a smoother idle with the stock cam and save some gas, also with your 3.31 gears unless you're running a high stall converter, a stock cam will also have quicker off-the-line acceleration - especially if you still have the original compression.

 

[David Womby]

I would guess that yes, you'll have a smoother idle with the stock cam and save some gas, also with your 3.31 gears unless you're running a high stall converter, a stock cam will also have quicker off-the-line acceleration - especially if you still have the original compression.

Thanks. I can't tell from the faded old receipts that I have whether there was anything done to the heads or crank or whatever to affect compression.

David

 

[Don Frelier]

If Muscle Motors put it together it should be a well built engine.
You might want something like shown below.
I wouldn't expect a huge economy increase maybe 3-4 mpg.
Do have a working vacuum advance?

I just searched for a 70 charger 318 from RockAuto: 1970 DODGE CHARGER 5.2L 318cid V8 Engine Parts | RockAuto

 

[Don67Satellite]

Get an AFR setup and see where the fuel is going.

I do agree with this. I recently had my buddy slap an AFR setup to my 440 and we ran her around & gave her a good tune up. Since I do not race and am only mildly over stock, I had also added a vacuum advance distributor, which combined, has seemingly increased my fuel mileage to some degree. This is determined by purely observing my fuel gauge heading for the big "E" less rapidly than before.

However, we both have V8 engines of similar vintage, so if we are being honest, what would be considered "good fuel mileage" is really out of the question. IMHO, I am not sure the savings will be worth the hassle of swapping the cam.

 

[David Womby]

I do agree with this. I recently had my buddy slap an AFR setup to my 440 and we ran her around & gave her a good tune up. Since I do not race and am only mildly over stock, I had also added a vacuum advance distributor, which combined, has seemingly increased my fuel mileage to some degree. This is determined by purely observing my fuel gauge heading for the big "E" less rapidly than before.

However, we both have V8 engines of similar vintage, so if we are being honest, what would be considered "good fuel mileage" is really out of the question. IMHO, I am not sure the savings will be worth the hassle of swapping the cam.

Pardon my ignorance but how is that done. A quick internet search seems to show an oxygen sensor stuck into the tailpipe and an analyzer attached. Is that it?

Yes, the vacuum advance is working.

Thanks, everyone, for the suggestions/advice. Much appreciated.

I am beginning to think maybe I need to take the car to somebody who has the equipment and knowledge to tune it. Anybody able to recommend anywhere preferably on the North/West side of Orlando?

David

David

 

[Curiousyellow71]

Is the vacuum advance working? How much timing.

 

[bobsgtx]

I don't know your abilities but this is what I would start with before changing any parts. Verify TDC on dampener. Take a compression test. Check plugs when they are out. Check timing at idle and full mechanical advance and rpm with vacuum advance disconnected and plugged. Check vacuum advance with vacuum pump and how much. Check engine manifold vacuum at idle. Write results down to figure out what you have and what to change. Make sure engine comes up to temperature. Just my opinion.

 

[Don67Satellite]

Pardon my ignorance but how is that done. A quick internet search seems to show an oxygen sensor stuck into the tailpipe and an analyzer attached. Is that it?

That's exactly how it is done. I was fortunate to have a O2 bung in my exhaust from the EFI setup that I removed. I just have a threaded plug in it now.

 

[1967coronet]

When it comes to carb choice a well tuned thermoquad will get your mpg. up as long as you keep your foot out of the secondaries.

 

[rumblefish360]

As I have posted in previous threads, I get pretty poor fuel consumption and a Muscle Car sounding idle. The idle would be great on the right car but not really suited to mine. My Bristol 408 had its engine replaced with one rebuilt in 1991 that I have the following info. for. I know it used .030" oversize pistons so it must now have slightly more than 360 Cu In. The transmission is a 1962 push-button 727 and the final drive is 3.31:1.

Your engine now displaces 365 cubic inches.
A 3.31 gear ratio on what size tire?
This is not a gear ratio known for mileage but the begging of mild street performance gears the factory offered.

1978 Monaco 360 engine.​

Mopar Performance Cam 4452761.​

Mopar Performance Intake Manifold P4529116.​

Piston rings 4.030"​

Pistons unknown​

Springs 998?​

The cam is what they called back in the day, the upgraded 340 cam because of the similar lift. The reality is, IIRC, it’s duration @.050 is 228*’s. This is a street performance cam.
It should be used with headers and a dual 2-1/2 exhaust. Roughly performing in the 1800-600 rpm area. It seems you have the valve springs to match the cam. The intake manifold is an aluminum copy of the earlier 340.

I am attaching a pic the specs I can find comparing the cam that is fitted and the stock 1978 Monaco 360 cam.

I think swapping my cam for a stock one is just about within my abilities but, before I try it, I expect a stock cam would reduce the idle noise and loping but would it also help fuel consumption to any significant degree?

I don’t understand the “Idle noise” because the cam does t have anything to do with noise being it is also a Hyd lifter cam. At the tail pipe, the cam, depending on a few factors of the cam, will introduce a rhythm to the exhaust. Like what you said earlier, that muscle car sound. If the engine itself is loud, this could be another issue.

I also wonder if any other type of carburetor (it has a relatively new Summit Racing Carb SUM-M08600VS. 600cfm) would help? Any advice or opinions would be appreciated.

I’m using the 750 vacuum secondary model on the same size engine. They are actually a very good carb that Holley used to make that resembles a old Ford carb. This carb uses all the Holley tricks and parts.

IF you go back to the stock cam, a 600 cfm would be a good size.
IF you stay with the current cam, I myself would use the 750.
Ether carb is a win. Nether carb will consume more fuel while driving normally. Just jet and tune the carb and your distributor and mileage and power will be there.

Been there and done that with those two exact carbs on stock engines and hot rodded engines.

David

View attachment 1358088

View attachment 1358089

That’s one cool car David.

The stock cam should net better mileage over the performance cam for several reasons.
1, simply being smaller, opening the valves less for less air and fuel.
2, If the bigger cam isn’t well complimented with the proper performance parts, it becomes inefficient and will waste gas, perform badly.

As said earlier, an 02 sensor for tuning the carb is an easy and quick way to get the carb tuned fairly well for sure. Nest would be the ignition. Huh powered is a plus but the distributor should be attended to for maximum return even with a stock ignition.

I have gotten 20 mpg w/a 360, BUT, my gear ratio was a 2.76 on 26-1/2 inch tires. The car was a ‘79 Dodge Magnum @ 4K lbs. with me in it.

 

[David Womby]

Your engine now displaces 365 cubic inches.
A 3.31 gear ratio on what size tire?

185R16 - 27.75" diameter

This is not a gear ratio known for mileage but the begging of mild street performance gears the factory offered.

The cam is what they called back in the day, the upgraded 340 cam because of the similar lift. The reality is, IIRC, it’s duration @.050 is 228*’s. This is a street performance cam.
It should be used with headers and a dual 2-1/2 exhaust.

Mine has stock cast iron manifolds then dual 2.25" pipes - no crossovers, one muffler per side.

Roughly performing in the 1800-600 rpm area. It seems you have the valve springs to match the cam. The intake manifold is an aluminum copy of the earlier 340.

I don’t understand the “Idle noise” because the cam does t have anything to do with noise being it is also a Hyd lifter cam.

My sloppy wording. By 'idle noise' I was referring to the loping and loudness at the tailpipes.

At the tail pipe, the cam, depending on a few factors of the cam, will introduce a rhythm to the exhaust. Like what you said earlier, that muscle car sound. If the engine itself is loud, this could be another issue.

I’m using the 750 vacuum secondary model on the same size engine. They are actually a very good carb that Holley used to make that resembles a old Ford carb. This carb uses all the Holley tricks and parts.

IF you go back to the stock cam, a 600 cfm would be a good size.

Current carb is 600cfm Summit SUM-M08600VS.

IF you stay with the current cam, I myself would use the 750.
Ether carb is a win. Nether carb will consume more fuel while driving normally. Just jet and tune the carb and your distributor and mileage and power will be there.

Been there and done that with those two exact carbs on stock engines and hot rodded engines.


That’s one cool car David.

The stock cam should net better mileage over the performance cam for several reasons.
1, simply being smaller, opening the valves less for less air and fuel.
2, If the bigger cam isn’t well complimented with the proper performance parts, it becomes inefficient and will waste gas, perform badly.

As said earlier, an 02 sensor for tuning the carb is an easy and quick way to get the carb tuned fairly well for sure. Nest would be the ignition. Huh powered is a plus but the distributor should be attended to for maximum return even with a stock ignition.

Fitted with
Distributor Pertronix PNX-D141701
Coil Pertronix PNX-45001

I have gotten 20 mpg w/a 360, BUT, my gear ratio was a 2.76 on 26-1/2 inch tires. The car was a ‘79 Dodge Magnum @ 4K lbs. with me in it.

I'd be happy to get 12mpg (btw, I run only non-ethanol gas)

David

 

[David Womby]

Is the vacuum advance working? How much timing.

I don't know your abilities but this is what I would start with before changing any parts. Verify TDC on dampener. Take a compression test. Check plugs when they are out. Check timing at idle and full mechanical advance and rpm with vacuum advance disconnected and plugged. Check vacuum advance with vacuum pump and how much. Check engine manifold vacuum at idle. Write results down to figure out what you have and what to change. Make sure engine comes up to temperature. Just my opinion.

I went through tuning/timing in the spring. Here's my notes from then

With vac plugged the car idles well in neutral at 900rpm with20BTDC timing and at about 750rpm in drive. The limiters are set to 14degrees. The mechanical advance starts at about 1100rpm and reaches 34 (the limiters hold it there, of course) at just before 3000rpm.

David

 

[toolmanmike]

You may be able to pick up a mile or two with a smaller cam. 360's were never a economy engine. A 3.31 ratio isn't optimal. A ratio in the 2.70's would be better.

 

[BSB67]

The MP 0.050" cam specs for all of their cams are BS. This cam would probably measure 218/221 @ 0.050" based on other MP cams that I have mesured. It only has 50 degrees overlap. I would characterize this as a nice upgrade from the factory cam but still relatively mild.

I don't think the OP ever told us his gas milage, and what he would like it to be. The OP should be getting 13 to 15 mpg under normal driving with that cam if everything else is right. Might get a few more with the factory cam

 

[David Womby]

The MP 0.050" cam specs for all of their cams are BS. This cam would probably measure 218/221 @ 0.050" based on other MP cams that I have mesured. It only has 50 degrees overlap. I would characterize this as a nice upgrade from the factory cam but still relatively mild.

I don't think the OP ever told us what his gas milage is, and what he would like it to be. The OP should be getting 13 to 15 mpg under normal driving with that cam if everything else is right. Might get a few more with the factory cam

Usually around 8mpg. Never above 10mpg. I'd like 15 but 12 would be OK.

David

 

[old guys rule]

As I have posted in previous threads, I get pretty poor fuel consumption and a Muscle Car sounding idle. The idle would be great on the right car but not really suited to mine. My Bristol 408 had its engine replaced with one rebuilt in 1991 that I have the following info. for. I know it used .030" oversize pistons so it must now have slightly more than 360 Cu In. The transmission is a 1962 push-button 727 and the final drive is 3.31:1.

1978 Monaco 360 engine.​

Mopar Performance Cam 4452761.​

Mopar Performance Intake Manifold P4529116.​

Piston rings 4.030"​

Pistons unknown​

Springs 998?​

I am attaching a pic the specs I can find comparing the cam that is fitted and the stock 1978 Monaco 360 cam.

I think swapping my cam for a stock one is just about within my abilities but, before I try it, I expect a stock cam would reduce the idle noise and loping but would it also help fuel consumption to any significant degree?

I also wonder if any other type of carburetor (it has a relatively new Summit Racing Carb SUM-M08600VS. 600cfm) would help? Any advice or opinions would be appreciated.

David

View attachment 1358088

View attachment 1358089

 

[old guys rule]

Take a look around the Mopar si.te for an old Edelbrock sp2p intake manifold and a holly 4175 650 CFM spread bore which will be much easier to tune for you then a quadrajet. Thermal quad parts are really difficult to find and are about as hard to tune as a quantity. The sp2p and 41 75 will give you about as much and increase in mileage as you can expect from any bolt on I really don't think swapping cams would be worth all the effort. Put your time and effort into your top end . Much easier and a very noticeable mileage increase.

 

[Runcharger]

Yeah, it seems off. I would be scared to change cams with parts available today. Lots and lots of lifter problems we keep hearing about. Myself I wouldn't downgrade to that 2bbl, stock cam anyway. 360's aren't natural gashogs IMO, I think something is wrong, vacuum leak or something. A 3.31 with a 27 inch tire should work quite well with your combination IMO.
I've gotten better than 8MPG with a street Hemi.