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Old 12/27/2007, 06:50 PM   #1
Mosesatm
 
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302 4V Heads on a 289 2V

It's my understanding that the 1968 302 4V heads are identical to the 1968 289 2V heads except they have smaller combusion chambers.

A smaller combustion chamber creates higher compression and thus creates more horsepower. Pretty simple so far.

Now for the part that confuses me;
Since the higher compression should create a more powerful explosion it seems that those heads would be more efficient than the lower compression 2V heads. With that in mind would the 302 4V heads also increase MPGs? More horsepower AND better mileage!

Any thoughts or experiences with this idea?
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Old 12/27/2007, 07:42 PM   #2
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Lots of variables here Arlie. Speaking only from a hypothetical standpoint, because I've never done this head swap, if you run higher compression, you would also have to adjust your timing and run a higher grade of gasoline, both of which would effect your mileage and performance. Additionally, if you run that 4V only at partial throttle, you are using smaller venturis than the 2V, basically a smaller carb, and increasing your mileage. If you run at wide open throttle, you are putting more fuel into the engine (such as 600 cubic feet/min instead of 450-500 CFM), which increases your performance at the expense of mileage. Never discount the human factor. My right foot is heavier than my left, and I have weak ankles so my right foot tends to hold the pedal to the floorboard, making any scientific comparison impossible. Ask Joe. It runs in the family.

Steve

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Old 12/27/2007, 08:27 PM   #3
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Sorry, Steve I wasn't clear enough. Same carb, just different heads.

I agree that the question is a bit unreasonable when the human factor is added. No one is going to drive the same after they acquire added horsepower.

But let's assume super-human willpower and everything being the same except the heads. I'm thinking about making the swap one of these days but if I can get better mileage out of the deal 'one of these days' may get here a little quicker.

Whatever illness Casey and Joe have seems to be spreading!
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Old 12/27/2007, 09:08 PM   #4
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Quote:
Originally Posted by Mosesatm View Post
Whatever illness Casey and Joe have seems to be spreading!
Hey... Watch out. I resemble..er, I mean ...I resent that remark. I choose to think of it as a positive characteristic, not an illness.

Joe

HP numbers are good and all, but they're like asking someone how much they can bench. What difference does it make, if I can still kick your ass.
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Old 12/28/2007, 03:00 AM   #5
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Hey... Watch out. I resemble..er, I mean ...I resent that remark. I choose to think of it as a positive characteristic, not an illness.
I Stand behind you on that Joe!
(...damn sure as hell wouldn't stand in front of you ;-)
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Tim
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Old 12/28/2007, 08:23 AM   #6
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Hey... Watch out. I resemble..er, I mean ...I resent that remark. I choose to think of it as a positive characteristic, not an illness.
I also forgot to mention that I inherited this "positive characteristic" from my Dad.

Joe

HP numbers are good and all, but they're like asking someone how much they can bench. What difference does it make, if I can still kick your ass.
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Old 12/28/2007, 10:35 AM   #7
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Quote:
Originally Posted by rvrtrash View Post
Never discount the human factor. My right foot is heavier than my left, and I have weak ankles so my right foot tends to hold the pedal to the floorboard, making any scientific comparison impossible. Ask Joe. It runs in the family.

Steve
Steve;
I totally agree with you. I tried that very theory while in California with Tim's car and it worked very well.

Now as for my own car, Instead of swapping heads to gain more compression, I swapped the whole engine (428CJ for the 390) and found that I ran into the same problem I had with Tims car. Heavy foot and weak ankles.

Arlie; I've never seen anyone do it that way (4V heads and 2bbl carb), You'll have to let us know how it does. I've seen folks swap out their 2bbl manifold for a 4bbl manifold and 4bbl carb but, leave the 2V heads on the motor. Talk about a waste of fuel and performance. And then they wonder why their car doesn't run well.

68 GT/CS 390 "S" Code, 4 spd, 93 LX Hatchback Supercharged
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Old 12/28/2007, 10:39 AM   #8
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Steve;

Arlie; Your going in the right direction. I've seen folks swap out their 2bbl manifold for a 4bbl manifold and 4bbl carb but, leave the 2bbl heads on the motor. Talk about a waste of fuel and performance. And then they wonder why their car doesn't run well.
Also, Arlie, at a minimum, I would port match the exhaust ports before installation. Those ports are horrible from the factory.

Joe

HP numbers are good and all, but they're like asking someone how much they can bench. What difference does it make, if I can still kick your ass.
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Old 12/28/2007, 11:41 AM   #9
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Geez, I guess my writing skills still suck.

Right now I have a Holley 4V carb and an Edelbrock intake sitting on '68 289 2V heads. I am thinking of switching to '68 302 4V heads to get away from the 8.7 compression ratio the 289 heads provide.

As Don noted, the engine feels like it's being strangled but the 302 and 289 heads use the same valves so I'm not sure the engine will breathe any better with the 302 heads, unless I gasket port them as Joe mentioned.

From what I've been able to research all the 302 heads do is raise the compression due to smaller combusion chambers. I don't know if the intake chambers are the same size. That'll take some more research to find out.

Of course, to pick up compression I could just get the heads milled.

The overall goal is to maximize power with out destroying mileage and I was thinking the 302 heads may be a win/win on both ends but the more we talk about it the more doubt I have.
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Old 12/28/2007, 02:53 PM   #10
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Arlie;
I thought you still had the 2bbl on your car. Sorry. With 2V heads your dumping a lot of raw gas into your heads that isn't being burned effectively. I would think by going to 4V heads you'd burn the fuel better thus picking up some better fuel economy as well as added power. Not knowing much about the small block heads, I'm not sure if the exhaust ports are the same size on the 2V 289 heads vs the 4V 302 heads. I know there is a difference between the 390 GT heads and the 428CJ heads when it comes to the exhaust ports.

Don

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Old 12/30/2007, 12:31 AM   #11
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Well the main consideration for carb size is your cam rpm. The standard calculation for this is cubic inch divided by 2. In your case with standard bore would be 151 times the max cam RPM (stock would be 5000. Max hp of a J Code was rated 230hp at 4800 RMP) divided by 1728. So if you have a 5000 cam it would be 151 x 2.89351 = 436 CFM. The 68 Autolight 4300 was rated at 440 CFM.
You could use a 2100 but you will flat line around 4000 RPM and never reach the full potential of your cam. If you want beter perfomance and great MPG consider a 2100 tripak from Pony Carbs, its pricy, about 1900 bucks (http://cgi.ebay.com/ebaymotors/Ford-...Z250050646659). If your goal is to build a stock sleeper go with a cam that has a lower RPM range that your 2100 can handel. All 68 2100 were rated at 356 CFM except the C8AF-AK and the C8ZF-G were rated at 287 CFM. If you have a 356 CFM your Max RPM would be aprox 4000 RPM if my math is right.
SOO you need 4000 RPM cam with at least a 112 Lobe Separation AND no mor than 220 lift at exh and intake or you will lose vacume which will result in poor idel. Also consider roller rail type rockers. A cam to look at would be http://store.summitracing.com/partde...0&autoview=sku. This would go well with an auomatic with a standard stall converter.
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Old 12/30/2007, 01:35 AM   #12
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Here are the roller rockers that fit: http://store.summitracing.com/partde...6&autoview=sku

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Old 12/30/2007, 08:14 AM   #13
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Arlie, I think I know where you're going now, so let me try again. My 302 has the "F" code heads which gave 10:1 compression. When I rebuilt the engine, I used a different piston to drop the compression ratio to 9.3:1, on the advice of my engine builder. The higher compression was meant to use premium gas, which in 1968 was 98 to 101 octane and he felt a slightly lower compression was better for todays 92 octane. I'd keep the heads you have for this reason. As to the mileage part, again hypothetically, if everything else stayed the same-carb,intake,fuel quality,exhaust,etc., you might get marginally better mileage, but not enough to justify the expense of the swap. I would imagine you could do just as well with a low restriction muffler. Hope this is what you were looking for.

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Old 12/30/2007, 09:45 AM   #14
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On the 4bbl heads they also used Flattop pistons to achive the 10:1 comp.
My J code came this way. Mine runs fine on Prem. Chevron gas.
Nates68
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Old 12/30/2007, 10:26 AM   #15
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I believe all the '68 302 pistons were flat top, regardless of compression ratio, heads or 2V/4V.

Steve

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