Selecting cam to work with A/C

-
G

gzig5

Well-Known Member
Joined
May 3, 2018
Messages
2,834
Reaction score
3,806
Location
Mequon, WI
What do I need to keep in mind when selecting a cam for my 340 that will see significant street, Auto-X, and road course driving, but I would like to be able to run an aftermarket Vintage Air type air conditioning unit to keep it comfortable in summer. I understand everything is a compromise. So given that I want as strong an engine as possible with good mid-range grunt for pulling out of corners and upper end power, where am I going to have to sacrifice on the cam specs? Or am I?
I currently have a quote from Mike Jones for close to max effort SFT cam (without A/C being considered) that comes up at 244/252 @.050" .365"/.364" Lobe Lift 108 LSA. Would that work with AC?
Basic outline is 3700lb car, 10.5:1 compression 340 with ProMaxx heads flowing ~250-270cfm depending on if I get them worked over. 1 3/4" headers, A833 4spd, 3.55 gear (may go to 3.91 or 4.10 later with an OD trans).
 
Take a look at the Lunatti 10200703. Long duration cams are not typically good for AC and power brake applications. 65'
 
gzig5 said:
What do I need to keep in mind when selecting a cam for my 340 that will see significant street, Auto-X, and road course driving, but I would like to be able to run an aftermarket Vintage Air type air conditioning unit to keep it comfortable in summer. I understand everything is a compromise. So given that I want as strong an engine as possible with good mid-range grunt for pulling out of corners and upper end power, where am I going to have to sacrifice on the cam specs? Or am I?
I currently have a quote from Mike Jones for close to max effort SFT cam (without A/C being considered) that comes up at 244/252 @.050" .365"/.364" Lobe Lift 108 LSA. Would that work with AC?
Basic outline is 3700lb car, 10.5:1 compression 340 with ProMaxx heads flowing ~250-270cfm depending on if I get them worked over. 1 3/4" headers, A833 4spd, 3.55 gear (may go to 3.91 or 4.10 later with an OD trans).
Click to expand...

I think it will depend largely on the idle quality of the cam you choose and what rpm you set the idle to. Mike can certainly tell you if the cam you mentioned is appropriate or if another grind might be a better choice.
 
I don't see why that cam shouldn't work. Surely you won't be running with the compressor on up to 6500 r's on a regular basis.....right :). Nudge the idle speed up a hun or so and you probably won't notice it. Easy with the 4spd.

I would make sure your cooling system is up to snuff. Hanging that condenser on there won't do you any favors.
 
I like Comp's version of the 340 cam. It's actually ground to take advantage of the .903 lifter diameter.
 
Plymouth 65 said:
Take a look at the Lunatti 10200703. Long duration cams are not typically good for AC and power brake applications. 65'
Click to expand...
This is the part that I wasn't sure of. The AC is an additional load on the engine, especially at idle or low rpm. But I don't remember the factory using a different cam if the car was equipped with AC, but most of the factory cams weren't really radical either. I'm not worried about vacuum, I'll probably be installing hydro-boost for the power brakes and steering. If I have to tweak the idle up a notch, that isn't the end of the world either. I'll definitely have the quotes updated to include AC but I was trying to get a little more background into what goes into it.
 
I would consider looking to your emission-era brethren for some tricks.
First, what ignition are you running? If it's a stock Mopar electronic ignition distributor, look at the dual-pickup models. There is the possibility that you can set the timing on the other pickup for a bit more retard at idle and a simple relay to kick it over when the AC is on at idle. This can help with idle and overheating.

A solenoid to kick the idle speed up is also an easily pirated item that can kick up your idle speed an adjustable amount when the AC is on.

A microswitch on the throttle will turn both on at idle when the AC is energized, and off when you're taking off or cruising. When the AC is off, the whole circuit will be off and it's just a normal non-air setup.

That's basically what the PCM in later Mopars do, just electronically.
 
My set-up is similar. The cam is a custom Hughes piece with 246/252 @ .050, .555"/.540" lift on a 108* LSA installed on 105* centerline. I have a 3700rpm stall lock-up converter and 4.30's with a 275/60-15 28" tall Drag radial. The ECU is supposed to take care of the A/C compressor drag, but the idle does drop about 50 rpm when its on. It's basically undetectable unless you really listed to it idle while the system cycles the pump on and off.

I'm running a factory Sanden compressor via the stock serpentine belt set-up, but I'm using the factory JTEC ecu to run EFI. So far, only an all wheel drive Nissan GTR pulled beat me out of the hole. With warm tires, the car almost dead hooks on the street. Around here the car is hard proven very hard to beat on the street. I know there are a lot of cars out there that would smoke me out of the hole and from 60+, but. I just haven't run into any of them yet.

Sometimes I forget to shut the A/C off, but I'm counting on the ECU to disconnect the A/C clutch at full throttle. Those Sanden compressors don't really take that much power to spin compared to the old school compressors.

Bcuda.JPG
 
jbc426 said:
My set-up is similar. The cam is a custom Hughes piece with 246/252 @ .050, .555"/.540" lift on a 108* LSA installed on 105* centerline. I have a 3700rpm stall lock-up converter and 4.30's with a 275/60-15 28" tall Drag radial. The ECU is supposed to take care of the A/C compressor drag, but the idle does drop about 50 rpm when its on. It's basically undetectable unless you really listed to it idle while the system cycles the pump on and off.

I'm running a factory Sanden compressor via the stock serpentine belt set-up, but I'm using the factory JTEC ecu to run EFI. So far, only an all wheel drive Nissan GTR pulled beat me out of the hole. With warm tires, the car almost dead hooks on the street. Around here the car is hard proven very hard to beat on the street. I know there are a lot of cars out there that would smoke me out of the hole and from 60+, but. I just haven't run into any of them yet.

Sometimes I forget to shut the A/C off, but I'm counting on the ECU to disconnect the A/C clutch at full throttle. Those Sanden compressors don't really take that much power to spin compared to the old school compressors.

View attachment 1715961428
Click to expand...

As I'm looking at using the JTEC in my car, I'm thinking more details about your car are required.
 
For comparison only;
I ran the Mopar 292/.509/108 cam for one summer on the street. I tried BOTH the Standard 2.66low A833 and the 3.09OD box, both with 3.55s. I ran it in a 367 with Alloy heads, @11.3Scr and 1.6 arms. So the cam is about the same as yours.
I didn't like either.
Forget trying to run the A833od with that combo The gears are just too far apart for a high-winding engine. The ratios are 3.09-1.67-1.00-.73od; with splits of .54-.60-.73.. that means that whatever you rev it to, on the shift the Rs will fall to those percents.
Your cam will want to be shifted at 6000, maybe a lil more with those nice heads. Therefore; on the 1-2 shift the Rs will fall to;
6000 x .54= 3240, and on the 2-3 to 3600. So then, your 340 will need some grunt down there.
Whereas the splits on the standard box are all at about .72 so;
.72 x 6000=4320 which will be close to the Torque-Peak.
You will need to gear your car pretty tight to the track.

I suggest the Commando box which has ratios of
3.09-1.92-1.40-1.00
Second gear with 3.55s and 27" tires, will get you from 53mph at 4500 to 71mph @6000.
The 3.09 first gear will help you get off the line with 3.55s, otherwise you'll be slipping the clutch quite a bit......... which is why I pulled that cam out.
Best of luck to you.
 
jos51700 said:
A solenoid to kick the idle speed up is also an easily pirated item that can kick up your idle speed an adjustable amount when the AC is on.
Click to expand...
Spot on.
This is what factory cars do, step up the idle speed to compensate for the AC.
It's simple and works..
They also have a different water pump pulley size as well to help with the low speed cooling.
 
AJ/FormS said:
For comparison only;
I ran the Mopar 292/.509/108 cam for one summer on the street. I tried BOTH the Standard 2.66low A833 and the 3.09OD box, both with 3.55s. I ran it in a 367 with Alloy heads, @11.3Scr and 1.6 arms. So the cam is about the same as yours.
I didn't like either.
Forget trying to run the A833od with that combo The gears are just too far apart for a high-winding engine. The ratios are 3.09-1.67-1.00-.73od; with splits of .54-.60-.73.. that means that whatever you rev it to, on the shift the Rs will fall to those percents.
Your cam will want to be shifted at 6000, maybe a lil more with those nice heads. Therefore; on the 1-2 shift the Rs will fall to;
6000 x .54= 3240, and on the 2-3 to 3600. So then, your 340 will need some grunt down there.
Whereas the splits on the standard box are all at about .72 so;
.72 x 6000=4320 which will be close to the Torque-Peak.
You will need to gear your car pretty tight to the track.

I suggest the Commando box which has ratios of
3.09-1.92-1.40-1.00
Second gear with 3.55s and 27" tires, will get you from 53mph at 4500 to 71mph @6000.
The 3.09 first gear will help you get off the line with 3.55s, otherwise you'll be slipping the clutch quite a bit......... which is why I pulled that cam out.
Best of luck to you.
Click to expand...
What's that got to do with the AC question?
What a pointless post..
 
AJ/FormS said:
And your post isn't?
Go back and re-read post #1, Maybe it will sink in, IDK.
Click to expand...
His main concern seems to be about compromising a cam because he wants to run AC..

gzig5 said:
I currently have a quote from Mike Jones for close to max effort SFT cam (without A/C being considered) that comes up at 244/252 @.050" .365"/.364" Lobe Lift 108 LSA. Would that work with AC?
Click to expand...
My post addresses that issue, did yours? If he runs a speed step up, he won't have to worry about compromising..
But feel free to tell us all about your gearbox with a cam he's not using..
( Which he didn't ask about)
 
The idle solenoid is a great idea and really leaves no reason to sacrifice your camshaft choice. So my recommendation taking that into consideration is to choose the camshaft you want. Remember though, most of them are not strong enough to kick the idle up unassisted on performance carburetors and throttle bodies, so you will have to tap the gas once the A/C is turned on. Some will do it though. Just food for thought.
 
gzig5 said:
What do I need to keep in mind when selecting a cam for my 340 that will see significant street, Auto-X, and road course driving, but I would like to be able to run an aftermarket Vintage Air type air conditioning unit to keep it comfortable in summer. I understand everything is a compromise. So given that I want as strong an engine as possible with good mid-range grunt for pulling out of corners and upper end power, where am I going to have to sacrifice on the cam specs? Or am I?
I currently have a quote from Mike Jones for close to max effort SFT cam (without A/C being considered) that comes up at 244/252 @.050" .365"/.364" Lobe Lift 108 LSA. Would that work with AC?
Basic outline is 3700lb car, 10.5:1 compression 340 with ProMaxx heads flowing ~250-270cfm depending on if I get them worked over. 1 3/4" headers, A833 4spd, 3.55 gear (may go to 3.91 or 4.10 later with an OD trans).
Click to expand...
Way to much cam for an a/c vehical. It will be very choppy and Lise low end torque. Kim
 
You must log in or register to reply here.
-

Back
Top