Stock Cylinder Head Flow Numbers Needed

Fresh Air Inspector

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Hello All,

It has been awhile since I'm been on the forum - just moved. As a result I haven't touched the '88 AHB Plymouth Caravelle (Gran Fury for you US guys), since May!!

I'm trying to calculate some camshaft specs for my engine as the Hughes item I was planning to use has an unknown delivery date. :-( Does anyone have the cfm vs. lift figures for the intake and exhaust ports on a stock, unmodified '302' head? Something captured via a proper flow bench like Superflow. I have searched all over and unable to find anything. Lots of stuff on aftermarket heads but nothing on the stock / unmodified heads.

Looking forward to the feedback.
 

Fresh Air Inspector

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Hello Duke5A,

Thanks for the quick response. The info is a step in the right direction. Although using aftermarket heads is the easy route, it is a very expensive one here in Canada. Ordering / purchasing anything out of the US ends up double to the price in Canadian dollars after the exchange rate + import duty + tax. I want to make sure I get the 'best bang for the buck'.

Looks like I have a lot more research to do.
 

AHBguru

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The heads you want are "308" heads from the '89-'92 LA360. The heads used on the squads from '83-'89 were 345 heads, which were modified 587 heads off the E58 engine. Only difference being larger coolant passages. The 308 head will give you a little higher compression and better flow than the 345.

Still, same old story - why all the work and money, when you could spend less on a good 360 Magnum.
 

Fresh Air Inspector

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Hello AHBguru,
Appreciate the feedback. Agree that the '308' and later '576' heads were the best production LA heads they can only be found on '88 - '92 LA360 truck engines. Although Mopar performance had them available until the early 2000s. Which makes them a rare item, although I am still on the look out for a set. I don't want to go the larger displacement or Magnum route - want to see what can be accomplished with the 318 roller I have in the car.

The search continues.
 

Ele115

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Still, same old story - why all the work and money, when you could spend less on a good 360 Magnum.
Work smarter, not harder. The above makes the most sense, and when it makes sense, it makes dollars and saves dollars.
 

AMC Diplomat

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I get what you're trying to do, but considering how difficult it is for you to get parts, just magnum swap it
This junkyard in Nova Scotia claims to have a 5.9l magnum
Screenshot_20240923_105853_Brave.jpg
I'm sure if you searched other years between 1992 and 2003 you could find more options for a 5.9l
Also: Magnum Swap -your source for Mopar engine swap information.
 

Mikes5thAve

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Go the 360/magnum swap. You can put a ton of time and money into the 318 and will stoll be ahead with a 360. Except in fuel mileage but if it's not a daily driver fun trumps mileage any time!
 

Ele115

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It used to be that you could just wake up an LA with high compression late 60's pistions, heads, manifolds etc. Now, those parts are pretty much gone or super expensive. I have just about run out of spare parts and on the last car I took apart I stumbled across a PRISTINE 5.9 magnum for $300 with a trans I could sell or save so it's a no brainer. Ten years ago I would reach into the pile and use the 68-70 pistons, heads and manifolds but I am down to my last set and a magnum swap would be about the same amount of work anyway so....
 

Aspen500

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5.2/5.9 Magnum's don't grow on trees anymore, considering it's been 20 or so years since the last one was made. Most of the trucks they were in are long since rotted away and gone (depending of course, where you live).
 

Duke5A

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The 5.9L is the best option, but has anyone asked what this guy wants to do? Maybe he has a low mileage motor he just wants to toss heads and a cam in?

If availability and budget is the concern then just do what the factory did with police motors and toss J heads onto your 318. Yeah, you lose a little compression, but it'll be more than made up for in flow.

And don't get caught up in the differences between casting numbers. All 340/360 heads are the same with the exception of intake valve size. Some had 2.02 and most had 1.88. You won't gain anything from the larger valve size on a 318.

Magnum head swap is always an option too. You will need a Magnum intake though.
 

kkritsilas

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There used to be the Engine Quest heads (essentially, the Magnum Heads without the head cracking issues, and improved flow characteristics) that were reasonable. I don't know what the situation is now in terms of availability and cost. I think the last I heard about them is that Hughes had started to carry them as well. Also brings up that the Magnum heads will interchange onto an LA engine, with some small issues to be looked out for.
 

AMC Diplomat

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out of curiosity... if it's an AHB, there's a chance it has police heads (might not, they came optioned all kinds of ways from the factory)
20240924_163617.jpg20240924_164253.jpg
 

Fresh Air Inspector

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Hello All,

Appreciate all the feedback, especially from Duke5A and AMC Diplomat. Unfortunately the thread went sideways which I was hoping would not happen.

For the record;

1. I'm only looking for flow numbers for the '302' head (if you have other stock flow numbers, please share), for reference purposes and to do some calculations. There is a ton of stuff out there for aftermarket heads with the type of numbers I'm looking for such as xxCFM@0.100", xxCFM@0.200" valve lift, etc. Unfortunately the info I have found for some stock heads simple says, for example; 123CFM but nothing about at what lift this takes place.

2. I have not touched my engine as yet, I started with the interior, underside and rear suspension so I have not checked the head casting number but I assume it is a '302' as the vehicle is an '88 AHB.

3. I'm not looking for huge HP or torque numbers. Target is 300HP at the engine and hopefully torque at 375 lb/ft or better. I like to see what an 'underdog' with some minor modifications will do.

4. If I wanted more HP and torque I would go with an RB engine (383 or 440), but that is not my goal. A nice cruiser with some decent horsepower mated to the A518 I have and the 3.55 Sure Grip I've already installed.

5. I want to use the original 318 as the base - it is low mileage 145K km / 90k mi (verified). Car was stored in a barn and last on the road 12 years ago. I also have some ownership history.

6. I do not want to go the 360 LA or Magnum route as I have already purchased the carb / manifold and numerous other engine bits for the 318.

Hope that brings my question back in focus.
 
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Mikes5thAve

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Check the casting numbers. If it was a 4bbl car they had different heads and even sitting for 12 years someone could have changed them before.
302s were big for a while like 20 years ago so the info was probably published at some point in a magazine. You might have better luck asking at moparts there's a lot more people there.
The plus side is anything you've bought for the 318 will work with an LA 360 if or when you do want more power and it's a basic swap.
 

Duke5A

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I found flow numbers from the Shady Dell Speed Shop on Archive.org. That place used to be THE place to get Mopar heads done and had a wealth of information on the site. Bad stuff went down and it was forced to close years ago.

When comparing flow numbers between heads it really should be done all on the same flow bench as there is variation between different ones.

302 Heads

LIFT-------AS CAST------PORTED

.100”-----51.8/N/A---------71.8/N/A
.200”-----92.5/70.7--------148.4/86.3
.300”-----130.1/104.3-----212.2/113.9
.400”-----163.9/113.2-----241.5/131.1
.450”-----169.1/115.2-----244.6/137.7
.500”-----170.4/117.3-----246.7/139.7
.550”-----172.2/119.0-----242.6/144.9
.600”-----172.5/120.4-----240.8/144.9

360 J Heads

LIFT------ASCAST---------PORTED
.100”----62.1/46.6---------62.1/51.8
.200”----112.1/99.4-------135.2/103.5
.300”----156.6/128.3-----198.7/135.2
.400”----193.2/137.3-----239.8/158.7
.450”----200.1/138.3-----253.9/169.7
.500”----200.1/139.7-----258.4/182.9
.550”----200.1/140.8-----264.9/186.3
.600”----200.8/141.5-----254.6/186.3


Like I said, Shady Dell was THE place. I would trust these numbers. Given your goals a set of freshened up 360 heads with a mild cam will get you near or at 300HP. You could reuse your factory exhaust manifolds as well up to that power level with 2.25" dual pipes. Should make for a mild mannered cruiser that can keep up with modern traffic.
 
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Fresh Air Inspector

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Hello Duke5A,

BRILLIANT!!! Exactly what I was looking for. Thanks for doing the detective work as well some additional tips.

Based on the flow numbers I would assume they were using 28 inches of water (pressure drop), to do this testing. This is the industry standard although some testers use 10 inches. SuperFlow developed a formula to convert; CFM28 = CFM10 x (28 / 10) x .5 where CFM28 = CFM at 28 inches of water.

As for exhaust manifolds I found an almost new set of cast iron 360LA truck manifolds (2.25" outlet). These should flow well although a set of 340 manifolds would be nice. I recognize that headers would be better but at ~$2K CAD (exchange, duty, tax, etc.) for a TTI set it is a bit much. Also, living beside the Atlantic Ocean takes its toll on headers unless ceramic coated.

I can't run dual exhaust as my car has the vent bubble on the top of the gas tank and it can't be moved to allow a drivers side pipe. Exiting before the rear wheels is also out as I want to keep the interior as quiet as possible. So, it will duals up to the muffler (2 in, 1 out), and then a single 3.5" tailpipe to the rear bumper.

Question - I assume you had to modify your floor tunnel to accommodate the A518 in your 5th Avenue?
 

Duke5A

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Hey, no problem.

If your manifolds are in good shape I wouldn't hesitate to reuse them. This article is what I'm basing my conclusion off of:

https://www.motortrend.com/how-to/mopp-0307-mopar-crate-engine-exhaust/
ezgif-7-24124f3c3b.jpg


318 manifolds at a 300HP level perform good. Don't spend money on new manifolds unless you have to and don't fret about flow differences between them. The differences are negligible.

You can still run duals if you want. 2.25" routes nicely over the axle and dumps right behind the rear tire. I used to have this setup and Dad has it on his coupe now only in 2.5". I always try and keep the exhaust sized where it needs to be to mitigate losses in velocity and to keep the noise down. If you want to go single then 3" would be more than enough. I know it fits as another member from years back ran a single 3" out to the bumper without having modify the tank.

Yup, needed to replace the crossover brace with a piece of flat stock that fits flush with the floor of the tunnel. Either that or you can use a piece of box tube and let it stick up through the floor of the car. With the carpet and seat in place it isn't noticeable. You'll need to make a custom trans mount too. It's honestly not that bad.
 

Mikes5thAve

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There's no problem moving the tank over its the typical 80s tank and has been done by many over the years.
 

Duke5A

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My '87 has the style tank where the vent protrudes from the tank and fits into a pocket in the trunk floor. The only option is to beat the shit out of the floor for clearance. I'm not sure when they changed to this style tank.
 
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