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Discussion Starter · #1 ·
I know this has been beaten to death here and I have read all the posts about this but I still have a couple of questions. I have a stock 318 with good compression in my 85 RC. This fall I need to be able to pull a 2 horse trailer (with horses) about 400 miles over a fairly decent range of mountains. I am on a very low budget but I have good mechanical abilities.

I currently have the stock 2 barrel carb. At the JY I found a q-jet carb for $50 and a stock cast iron 4 barrel manifold (probably from a 360) for $25. I know the ports are probably larger on the manifold than the ports on my 318 heads. I am still trying to identify which specific q-jet I have and then I'll rebuild it.

What I'd like to do is put on the q-jet with the cast iron manifold and probably put in a better cam (suggestions?) and a new/better timing chain. Later I will put on 3" single exhaust and a high flow cat and muffler.

The questions are: Is the carb & manifold worth doing without either port matching the heads or getting different heads? Will the 3" exhaust be worth doing without headers? Does a new cam require new value springs? Is there anyway to change value springs without pulling the heads?

Thanks,
d.t.
 
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I would say yes to all three questions. If you're not looking for mega horsepower, the port matching really won't matter. (Others will disagree) Check the Hughesengines.com web site for the cam. They have a great section explaining the workings of a cam. If you don't change valve springs with a new cam, you will never get the full benefit of the cam's performance. Check your cam bearings for any sign of wear before installing the new cam and always use new lifters. You can get a valve spring remover from places like Summit Racing that will let you replace springs without pulling the heads.
 
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Disagree? Me? Okay. Look. Will you see a performance improvement with the 360 intake and 4v carb? Yes, but only part of what you could have with a proper match. Even Mopar didn't swap intakes without adding the matching heads. The problem is the slower velocity in the intake will not atomize the fuel as well as a proper match would, and then you have dropout at the smaller head port and turbulence that impedes flow. This will hinder torque production. Either bite the bullet and get a standard Performer intake (or an SP2P on eBay) or add 360 heads for best performance. A good RV grind for a cam, something in the .430-.450 range, would be a great improvement. A new higher lift cam will only accelerate the wear-out of the older springs, and they may bind if lift is great enough, not to mention floating the valves at higher rpm because they'll be outmatched by the other upgrades.
 
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See. I told they would disagree :)

By using the 360 heads, you will drop your compression ratio due to the larger chambers. Which is worse than creating a mismatch between ports. If you're worried about that mismatch, then by all means, go with the Performer intake. It's designed for the 318 anyway. With the tight budget, I would go with the stock manifold. Gen is right about the mismatch, but in my opinion, it's not going to make that much difference in a truck built for hauling.
 

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PrimerGrey said:
I would say yes to all three questions. If you're not looking for mega horsepower, the port matching really won't matter. (Others will disagree) Check the Hughesengines.com web site for the cam. They have a great section explaining the workings of a cam. If you don't change valve springs with a new cam, you will never get the full benefit of the cam's performance. Check your cam bearings for any sign of wear before installing the new cam and always use new lifters. You can get a valve spring remover from places like Summit Racing that will let you replace springs without pulling the heads.
I agree with what he said. There will be an improvement with just slapping a 4 bbl manifold on it cause guys have done it and told me it helps. You would really gain more with going with an edelbrock performer that uses smaller ports that more closely match the 318 ports. If you go with 360 heads have them milled about .030" to increase compression. Factory 318 4bbl engines had about 7.5:1 actual compression ratio and still ran hard, but milling heads would make it run even harder. I use mopar performance cam with .430/.450 lift and make sure to degree it in, might even advance it 2 degrees. Use the right springs with it.
 

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chrysler300le said:
PrimerGrey said:
If you go with 360 heads have them milled about .030" to increase compression.
If one mills the 360 heads .030" will the intake still match up or will it need to be machined also? What about pushrod lengths with the somewhat shorter head?

Good advice all, can y'all reccommend a brand head gasket of the proper thickness to keep from losing compression?

Cheers

Chris
 

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im facing the same sort of delima. i have a 318 2 bbl and also have a thermoquad 4bbl with intake. also have 318 heads from a 4bbl. i was told that a 2bbl produces more torque (which is more important for offroading) than a 4bbl while a 4 bbl produces more horsies.
also was told 318 4bbl and 2bbl heads were the same.
 
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There's no such thing as 318 4bbl heads. If the 318 had a 4bbl, it had 360 heads and 360 intake. ANything that helps the 318 breathe will make more power, naturally, a 4v will make more hp.
Does anyone here see $3/gallon gas looming on the horizon? Leave the heads alone if you go 360. The lower compression will easily be handled by a recurved distributor with quick advance. If you must try a higher CR, use the thin gaskets. That'll give you an extra .020 squish and no milling...just in case. Remember that a good RV cam will build greater cylinder pressure right where your ignition is dialing in the advance. If it rattles, you either have to run higher octane, or dial the ignition timing back. A low compression engine will produce more useable power than a higher compression engine running limited advance...and "ping" kills power and mileage. You can dial in max advance and still get away with running on regular......unless you like paying at least 20 cents extra/gallon while filling up (30 gallon tank anyone?). Properly matching parts will yield the best results. It'll run all day long in the heat, on regular gas, and it won't knock. With SMOG (8:1CR) 360's capable of 335hp/400lbs torque in a totally streetable package, I wouldn't worry too much about that loss of CR.
 

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You will never get too much compression with 360 heads on a 318. Mill them .040 or .050 and it still won't ping. More compression makes more torque and uses less fuel because efficiency increases. I just use regular Fel-pro gaskets. They are probably a tad thicker then originals.
 

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And, to change the valve springs, if you leave the heads on, bump it around till the piston on the chosen cylinder is down... stuff a bunch of clean nylon or cotton braided rope into the spark plug hole, then turn the engine with a wrench, till the piston comes up and squishes the rope tight against the head/valves,... use a simple lever compressor to replace the springs.
 
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chrysler300le said:
You will never get too much compression with 360 heads on a 318. Mill them .040 or .050 and it still won't ping. More compression makes more torque and uses less fuel because efficiency increases. I just use regular Fel-pro gaskets. They are probably a tad thicker then originals.
Never? Gee, that's funny. I did, back in 1988 with my 318-powered '69 Charger. Before I knew better, I was all worried about 1/2 point of CR, so since 360 heads were the thing to do, and any loss of CR was a "bad thing," I had the heads milled .030, and learned how wrong that was. I had to retard the timing even with premium fuel, where it'd still ping on hot summer days down south. I went back to the 318 heads, returned the timing to a more appropriate level (ear and drive tuner-no timing light back then). Torque returned, and so did that missing 1- 1 1/2 mpg. The 360 parts made more top-end power (if it wasn't too hot outside), but that was seldom the case. The cam was the CompCams 260...very similar to the RV grinds mentioned here (I mention this to recall the cylinder pressure-building characteristics of these cams, which makes conditions more conducive to pinging...particularly in the mid-range. It's a lot more than just the static compression ratio you're dealing with). Now, looking back, maybe a richer mixture might've covered the ping. Maybe a different vacuum cannister on the distributor would've helped, but not much. 180-stat didn't help much either. The fact is, even if it doesn't ping initially, it will "carbon up" within a few thousand miles, and this will up the CR anyway. Then the only alternative is to reduce timing, unless CR can be reduced with thicker gaskets. If you mill til you're close to max CR for pump gas, it won't be long before trouble starts. The first rule on an engine is to not over-cam. The second should be, easy on the compression. All I'm saying is, don't sweat the CR. If ya wanna mill it, go for it.
 

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Lol 2 horses and a 2 horse trailer, lmfao just get in and go stop with the questions it's fine the way it is, just add a tranny cooler for good measure, have fun and enjoy the trip
 

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Discussion Starter · #13 ·
ED-3, ssshhhh! Don't let me wife hear you say that! I told her I "HAVE" to do all the performance upgrades in order to pull a trailer. ;)

Seriously, I haven't ever pulled a trailer except pulling an ordinace trailer behind a duece&1/2 in the Army 20+ years ago. The RC just seems pretty wimpy even without a trailer so I thought more power would be required to pull a trailer over an 10,000 foot pass.

And I DO intend to enjoy the trip, Thanks!
 
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Gen, I agree with what you're saying, but LinuxMan lives in Colorado. We can get away with more compression here because of the thinner air. But we can't get away with less. You lose approximately 3% cylinder pressure per every 1000 foot gain in elevation. Which means a motor pulling 150 psi at sea level will only be producing 105 psi at 10,000 feet. We have mountain passes that top 14,000 feet. Your 8:1 CR figure will be more in the range of 7:1 or less (effectively) at these altitudes. The untouched 360 heads would kill performance here.
 
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gen1dak said:
Well Hell, I didn't know he lived up there. That makes a big difference. Okay. Nevermind.
No, Gen, I admire your knowledge. I always read your posts with great interest. It's just that, at this altitude, we have to be more concerned with the cylinder pressures. I envy you guys that don't have to worry as much about it.
 

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Well i can say from personal experience I've put 360 heads that were milled .030" on top of a 318. No EGR valve and timing set at 35 degrees total and it has never pinged once with 87 octane gas. I'm also at about 600 feet above sea level. Also had MP 260/268 duration cam. I've also had 318's with stock heads that I couldn't get to stop pinging untill i hooked the EGR valve back up
 

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Discussion Starter · #18 ·
Thanks all for the advice and information. BTW, I did know that I lived in Colorado but I didn't understand the impact of altitude on compression etc.. Thanks Primer!

When we talk about port matching the heads, is it just on intake ports? (I do own a die grinder :-\) How much metal are we talking about? How smooth/polished must the new surface be?

Could I use the 360 intake manifold gasket to scribe the desired size, stuff a bunch of clean rags in the intake ports and grind them without taking off the heads? Then when done vacume out the port really well before removing the rags.

In case you haven't guessed I REALLY don't want to pull the heads and deal with the rusted exhaust manifold bolts, crusty exhaust pipe bolts, smog stuff and I usually wind up dumping at least some water into at least one cylinder.
 

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LinuxMan said:
Thanks all for the advice and information. BTW, I did know that I lived in Colorado but I didn't understand the impact of altitude on compression etc.. Thanks Primer!

When we talk about port matching the heads, is it just on intake ports? (I do own a die grinder :-\) How much metal are we talking about? How smooth/polished must the new surface be?

Could I use the 360 intake manifold gasket to scribe the desired size, stuff a bunch of clean rags in the intake ports and grind them without taking off the heads? Then when done vacume out the port really well before removing the rags.

In case you haven't guessed I REALLY don't want to pull the heads and deal with the rusted exhaust manifold bolts, crusty exhaust pipe bolts, smog stuff and I usually wind up dumping at least some water into at least one cylinder.
You hang the 360 gaskets on the head like they would be when installed. You then use a marker to mark the area you want ground out. Its only something like an 1/8 inch of metal all the way around. You need an even gradual taper back into the port. For surface finnish, you want a rough surface about as rough as the orignal or just a little smoother. Polishing is only for high rpm. The rough surface helps to keep the fuel suspended. Repeat this on the intake manifold (the stock castings don't even match the gasket).

The idea of porting it while still on the engine makes me cringe. I really don't like that idea, but if your are really thorough in your cleaning....
 
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