Deciding on replacement intake (318, details in post)

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J1MMY

J1MMY

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Current engine/drivetrain in my valiant is as follows:

318
167 KB pistons
360 heads ported
Lopey Isky cam (exact spec unknown but it seems there’s only 2)
Solid lifters
273 rockers
HEI distributor
Tunnel ram w/dual 450 carbs
Long tube headers
4 speed
3.91 explorer rear w/locker

There may be other mods as well but these are not known to me, no idea on output but it runs healthily and pushes the car along very nicely.


It may seem mad to some but my intention is to remove the tunnel ram & 450s and replace with something I can either get under the hood or a low hood scoop.

Reading on intake choice has pickled my newbie brain - air gap, RPM, or an altogether different choice? Car is not a daily driver, weekend/sunny day fun and the odd trip down the strip.

Advice is always appreciated.
 
Edelbrock Performer RPM, it is about 3/4" shorter than the air gap and should be fine. It will clear the hood; you might need to run a drop base air cleaner. Makes nearly as much power as the Air Gap.
 
Heywodja said:
Edelbrock Performer RPM, it is about 3/4" shorter than the air gap and should be fine. It will clear the hood; you might need to run a drop base air cleaner. Makes nearly as much power as the Air Gap.
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Is that edelbrock #7176? Oddly there’s one just up for sale near me
 
Do you know what the cylinder heads flow? Mabe the tunnel ram was ported to match. The ram is going to flow more no matter how much porting you do to any single 4 barrel intake. Figure that a rpm airgap which is the popular manifold of choice, is not going to flow over 240 cfm with the best of porting. So going the single 4 barrel route you may be disappointed if your heads flow more and your new manifold is the new choking point in your combination.
 
I doubt a RPM will choke off a 318 and will still give it the upper mid range that engine needs.

With the stick and 3.91's, make sure you get a mech. secondary carb of your choice, 750ish should fill the bill.
 
I hate to flog a dying point, but the Scr of that engine with open-chamber heads, is likely not gonna exceed 8.5/1
With a lopey cam, having an Ica around say 66* the cylinder pressure might already be in the basement... like 125psi; which means the vacuum signal to the venturis is gonna be ........... um, sluggish.

If it was mine, I'd be doing a compression test ASAP.
If it really is down around 125psi, I'd be rethinking a lotta things.
 
I've run an rpm airgap and a Victor 340, both with fitech tb which is about a 1/2" taller than most carbs. I run a typical drop base cleaner and it just barely clears the stock hood with the thicker van engine mounts I'm running. Doesn't ever touch though.
 
AJ/FormS said:
I hate to flog a dying point, but the Scr of that engine with open-chamber heads, is likely not gonna exceed 8.5/1
With a lopey cam, having an Ica around say 66* the cylinder pressure might already be in the basement... like 125psi; which means the vacuum signal to the venturis is gonna be ........... um, sluggish.

If it was mine, I'd be doing a compression test ASAP.
If it really is down around 125psi, I'd be rethinking a lotta things.
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Boy you took a dump on the posters thread.

How about a positive point?
 
dowboy1970 said:
Boy you took a dump on the posters thread.

How about a positive point?
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It’s ok he makes a fair point, I’ve done some searching through the posts before asking the question. I’ve got time over the festive break to do a compression test, which I will do as it’s good to have the clarity but given how the car pulls I’m not expecting low c/r. :)
 
ch1ll said:
Do you know what the cylinder heads flow? Mabe the tunnel ram was ported to match. The ram is going to flow more no matter how much porting you do to any single 4 barrel intake. Figure that a rpm airgap which is the popular manifold of choice, is not going to flow over 240 cfm with the best of porting. So going the single 4 barrel route you may be disappointed if your heads flow more and your new manifold is the new choking point in your combination.
Click to expand...
From what I’ve been able to find out the tunnel ram was added some time afterwards by a subsequent owner. I certainly appreciate your point, the basis behind the question was with this in mind.

No idea what the heads flow.
 
318willrun said:
factory cast with a 800 cfm Thermoquad :)
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Why does it seem like everyone what's to put 360 heads on their 318's? I asked these because they drop the compression off unless you have them milled like 0.070" and that has to cause port alignment issues also wouldn't that affect the push rod length? Just asking as I don't know these things as a fact or from personal experience.
 
Dan the man said:
Why does it seem like everyone what's to put 360 heads on their 318's? I asked these because they drop the compression off unless you have them milled like 0.070" and that has to cause port alignment issues also wouldn't that affect the push rod length? Just asking as I don't know these things as a fact or from personal experience.
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I've put 360 heads on 318's more than once, and I've always gained performance. Flow over compression. I always cut them about .040
 
J1MMY said:
From what I’ve been able to find out the tunnel ram was added some time afterwards by a subsequent owner. I certainly appreciate your point, the basis behind the question was with this in mind.

No idea what the heads flow.
Click to expand...
You stated that your car runs healthy and pushes the car along nicely. I took this as such that the person that built the engine matched parts and put together a good combination. Even if someone else added the tunnel ram with dual quads later, it takes good bit of knowledge and experience to tune that setup, especially for the street. With this in mind, I believe you will decrease performance going to a single 4barrel manifold setup, unless your car does not perform as good as you think it does.

Compression does matter, the more it has, the more horsepower it will make. That doesn’t mean your car won’t be quick, but it won’t have the horsepower to mph.

Case in point. I have a 68 dart that had a teener in it with a stock x head top end on it with the exception of a holley 650. It had a wild crower hydraulic cam and 4.55 suregrip. It ran 14 flat in the quarter mile, matter of fact I had it into the 13’s with a looser converter but it kept busting transmission tail pieces cause the frame/unibody was not stiff enough. But the car hit the eighth mile mark at 100 mph and would not go any faster cause it didn’t have enough compression. Low static and when you added in the cam overlap, the dynamic compression dived.
 
ch1ll said:
You stated that your car runs healthy and pushes the car along nicely. I took this as such that the person that built the engine matched parts and put together a good combination. Even if someone else added the tunnel ram with dual quads later, it takes good bit of knowledge and experience to tune that setup, especially for the street. With this in mind, I believe you will decrease performance going to a single 4barrel manifold setup, unless your car does not perform as good as you think it does.

Compression does matter, the more it has, the more horsepower it will make. That doesn’t mean your car won’t be quick, but it won’t have the horsepower to mph.

Case in point. I have a 68 dart that had a teener in it with a stock x head top end on it with the exception of a holley 650. It had a wild crower hydraulic cam and 4.55 suregrip. It ran 14 flat in the quarter mile, matter of fact I had it into the 13’s with a looser converter but it kept busting transmission tail pieces cause the frame/unibody was not stiff enough. But the car hit the eighth mile mark at 100 mph and would not go any faster cause it didn’t have enough compression. Low static and when you added in the cam overlap, the dynamic compression dived.
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Food for thought.

Expanding on the conversation then, I will get compression readings over Xmas. I cannot comment on the state of tune of the tunnel and carbs as do not know how well it is set up, a dyno run would give that info and tbh I hadn’t considered it. How well would a cross ram intake (if they’re available) weigh up?

And yes, agreed - performance without figures is a subjective thing.
 
Dan the man said:
Why does it seem like everyone what's to put 360 heads on their 318's? I asked these because they drop the compression off unless you have them milled like 0.070" and that has to cause port alignment issues also wouldn't that affect the push rod length? Just asking as I don't know these things as a fact or from personal experience.
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You are all wrong. As stated in post #17, a .040 cut and you have about 65cc chambers in comparison with 68cc 318 chambers. If you also mill the intake side of the head .038 the ports line up perfectly. You go from 170 cfm to 190 cfm or better. Since he is running 273 solid lifter rocker gear, the adjustment will take up and pushrod difference, and probably be closer to ideal. My two cents would be a Holley Strip Dominator intake and Thermo-Quad. Or whatever carb you are most comfortable with. As a side note, those pistons should give about 9.5:1 compression with 65cc chambers and about 9:1 with 72cc chambers. What compression does anyone think can you run on pump gas?
 
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AJ/FormS said:
I hate to flog a dying point, but the Scr of that engine with open-chamber heads, is likely not gonna exceed 8.5/1
With a lopey cam, having an Ica around say 66* the cylinder pressure might already be in the basement... like 125psi; which means the vacuum signal to the venturis is gonna be ........... um, sluggish.

If it was mine, I'd be doing a compression test ASAP.
If it really is down around 125psi, I'd be rethinking a lotta things.
Click to expand...
At least he's got the KB167's. Starting out at zero deck (or .001 below) is a good start. All the charts say 65-73cc for the 360 heads. How much compression with a .027 or a .040 head gasket? And yes, the op should do a compression test to make sure. There are a lot of unknown's here.
 
318willrun said:
I've put 360 heads on 318's more than once, and I've always gained performance. Flow over compression. I always cut them about .040
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Do you use the 5.9 heads or non magnum heads? I understand about flow but how much does the compression loss cost in performance
 
Dan the man said:
Do you use the 5.9 heads or non magnum heads? I understand about flow but how much does the compression loss cost in performance
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thay talking j heads the magnum head was used on both 5.9 and 5.2s with a 59ish cc chamber, probably closer to 62ish!! after a .040 cut the j's come in around 65ish depending on how far off factory was to there own specs! what lil compression is lost is not noticeable, better cylinder filling by better heads might not lose a .01 of compression at rpm!
Dan the man said:
Why does it seem like everyone what's to put 360 heads on their 318's? I asked these because they drop the compression off unless you have them milled like 0.070" and that has to cause port alignment issues also wouldn't that affect the push rod length? Just asking as I don't know these things as a fact or from personal experience.
Click to expand...
cause it works!!! any alignment of the ports can be fixed with gasket matching! .040 off the heads ant much, and with adjustable rockers is a non issue, with hydraulic lifters it ant nuff to worry over ether! better flowing heads will always make better power!
 
dirty white boy said:
thay talking j heads the magnum head was used on both 5.9 and 5.2s with a 59ish cc chamber, probably closer to 62ish!! after a .040 cut the j's come in around 65ish depending on how far off factory was to there own specs! what lil compression is lost is not noticeable, better cylinder filling by better heads might not lose a .01 of compression at rpm!

cause it works!!! any alignment of the ports can be fixed with gasket matching! .040 off the heads ant much, and with adjustable rockers is a non issue, with hydraulic lifters it ant nuff to worry over ether! better flowing heads will always make better power!
Click to expand...
Thanks for the info
 
J1MMY said:
Food for thought.

Expanding on the conversation then, I will get compression readings over Xmas. I cannot comment on the state of tune of the tunnel and carbs as do not know how well it is set up, a dyno run would give that info and tbh I hadn’t considered it. How well would a cross ram intake (if they’re available) weigh up?

And yes, agreed - performance without figures is a subjective thing.
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Probably the next best thing to a tunnel ram but, the tunnel ram will beat it by a large margin. Then you are starting from square one tuning 2carbs on a way different manifold and unported at that. You need to have a new manifold ported to match the port job on your heads. Is it all that important to get everything under the hood? I would leave it as it is and work on improving the setup as is if you want to increase performance.
 
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