Cam suggestions?

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HotrodColt

HotrodColt

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Yep, another topic that’s been beat to death but I can’t find much in the way of a combination using the parts that I have. I have a 318 that was pulled from a 74 motorhome, however, after running the numbers on it, it’s a 68 engine with forged crank, 340 rods. Appears to measure to a stock bore size, can still see the cross hatch in the bores and there’s no ridge. It has the closed chamber 234 heads from a 273. I want to put this engine back together with a few modifications. I’m going to run an edelbrock 340 single plane intake, but I’d like to know which cam I should pair with these heads. Most I’m going to do to the heads is port work, keeping stock valves, May upgrade the springs depending on the cam. I was looking at the Hughes whiplash but it says not to run over 8.9cr and my understanding is that these heads put it at 9.1cr. Also thought about the comp Thumpr. Keeping stock converter, gears are negotiable.
 

As far as the cam goes I would use something on 108 centerline in the 268 advertised duration range. Single plane is a mismatch even a Edelbrock performer would be a better fit. But I understand using what you have and it will work. To begin to take advantage of your suggested parts you will need at least 3.50 or plus rear end gears. Upgrading the valve springs definitely. I also believe that whiplash cam would be a good fit.
 
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205-215 intake duration, if wanting to keep mild with stock stall and gears, 215-225 if you want to step it up especially with gears (3.55-3.91+) and stall, I agree single plane isn't the right fit, especially with a 318 don't want to throw away more low end power than you have too.
 
I'd do something like a comp XE262 type of .050 duration (218@.050) with as much lift as possible max, but more like an XE256. with replacement composite head gaskets your compression ratio will likely be lower. you have to actually measure everything to calculate the compression ratio
 
Motorhome 318 with 234 heads so a quick question is in order... Does it have 18mm spark plug threads and did it have the big industrial water pump on it? Be aware that it may have a water instead of exhaust crossover on the head. That's not a huge deal if you get your exhaust crossover in the intake welded up (I've used epoxy mixed with coarse steel wool and sanded it smooth on the cheap) and use Felpro 1243 blocked crossover gaskets. Fel-Pro 1243 Fel-Pro Performance Intake Manifold Gasket Sets | Summit Racing If so, valves would be poly size 1.84 intake and 1.56 exhaust size and always set up for rotators from what I have seen. Eliminating the exhaust rotators on those is nearly impossible without changing exhaust valves.
 
Garrett Ellison said:
Motorhome 318 with 234 heads so a quick question is in order... Does it have 18mm spark plug threads and did it have the big industrial water pump on it? Be aware that it may have a water instead of exhaust crossover on the head. That's not a huge deal if you get your exhaust crossover in the intake welded up (I've used epoxy mixed with coarse steel wool and sanded it smooth on the cheap) and use Felpro 1243 blocked crossover gaskets. Fel-Pro 1243 Fel-Pro Performance Intake Manifold Gasket Sets | Summit Racing If so, valves would be poly size 1.84 intake and 1.56 exhaust size and always set up for rotators from what I have seen. Eliminating the exhaust rotators on those is nearly impossible without changing exhaust valves.
Click to expand...
It did have the water pump and I believe it does have the water crossover, however, I’m not entirely sure with it being a 68 engine that came from a 74 motorhome. Can I just weld up the holes on the heads? Are exhaust rotators an issue? Haven’t pulled the plugs from the heads yet.
 
Exhaust rotators are thick and have shorter than standard springs. It’s up for debate how much exhaust lift you can safely run with rotators, but most checks show somewhere below .440 actual valve lift. Stock rockers usually have a closer to 1.4 than a 1.5 ratio. When combined with the 58 degree lifter angle, you can sometimes get lucky and get by with having more cam lift than what is actually available at the valve, but “luck” isn’t a good game to play here (about like being lucky when playing Russian Roulette). But that’s still a lot of weight without a lot of valvespring to help control it, so you’re probably not going to see a lot of benefit from your performance cam with them.
 
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As far as plugging the ports in the heads, my late machinist told me he had drilled and tapped similar heads for recessed Allen pipe plugs, but I thought the heads looked a little thin in that area. It probably does get thicker farther from the opening. I do know that these heads with some bowl work and going with 1.88/1.60 valves with a good multi angle valve job would make a significant improvement and remedy the rotator issue as well. If the guides need redone, then going over to a pair of 11/32 stem 1.94/1.60 .100 longer Chevy valves would be a nice step forward, and even more so with some home port work.
 
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Garrett Ellison said:
As far as plugging the ports in the heads, my late machinist told me he had drilled and tapped similar heads for recessed Allen pipe plugs, but I thought the heads looked a little thin in that area. It probably does get thicker farther from the opening. I do know that these heads with some bowl work and going with 1.88/1.60 valves with a good multi angle valve job would make a significant improvement and remedy the rotator issue as well. If the guides need redone, then going over to a pair of 11/32 stem 1.94/1.60 .100 longer Chevy valves would be a nice step forward, and even more so with some port work.
Click to expand...
NAPA used to offer some self tapping screws. You screwed them and broke them off with a hammer and ground them down flat. They worked really well.
 
For what sounds like is shaping up to be a pretty basic warmed over 318 build………I’d be trying to make my life easier in the cylinder head dept and not use heads with the water crossover.
It’s not like regular 318 heads are scarce.
 
HotrodColt said:
Yep, another topic that’s been beat to death but I can’t find much in the way of a combination using the parts that I have. I have a 318 that was pulled from a 74 motorhome, however, after running the numbers on it, it’s a 68 engine with forged crank, 340 rods. Appears to measure to a stock bore size, can still see the cross hatch in the bores and there’s no ridge. It has the closed chamber 234 heads from a 273. I want to put this engine back together with a few modifications. I’m going to run an edelbrock 340 single plane intake, but I’d like to know which cam I should pair with these heads. Most I’m going to do to the heads is port work, keeping stock valves, May upgrade the springs depending on the cam. I was looking at the Hughes whiplash but it says not to run over 8.9cr and my understanding is that these heads put it at 9.1cr. Also thought about the comp Thumpr. Keeping stock converter, gears are negotiable.
Click to expand...
The 234 heads run water through the heat crossover. You're going to want to block that off at the head with a plug or a plate at each side of the intake manifold.. or use a manifold that doesn't have a heat crossover.. like a rpm air gap, vic, strip dominator etc..

Those heads are nice because the exh ports are blind 'no flow disruption' since they run coolant into the crossover instead of exhaust..


Single plane? Which, the torKERr,?
Not my favorite.

A cam with a 108 or narrower lsa is the direction id go.
 
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They also look like they’ll pretty handily open up to a 1243 gasket on the intake side, too, save for the pushrod pinch. I’d still like to see more port volume, though!
 
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