2bbl head on 4bbl engine question

68GEETEE · Dec 20, 2003

last year I had the heads rebuilt on my '68 302 4bbl. The engine block is the original and it is a J code (4bbl). While the heads were off I took notice of the numbers and found out the the heads are actually off of a '70 motor. Is this ok, since the 70 302 was strictly a 2bbl engine that year? Is it hurting anything, performace, etc? I have had engine pinging problems and am running 93 octane chevron gas, have set the dwell, adjusted the timing, new plugs cap rotor wires, I am wondering if the 2 bbl heads are causing a problem?

P.S. I recently got a pair of '68 4V heads numbers matching for my engine. I just wasnt in a rush to put them on, but I will if they are gonna make a huge difference.

65fastback2+2 · Dec 20, 2003

yes, its a performance problem. I only know this from reading loads of posts on the vw site i run, many people try to throw 16v heads on a 8v block. This severly lowers compression. If you take a 8v vw block and put 16v heads on it you get like 7:1 compression. You would do good to get those matching heads on and get everything breathing at the same rate. Right now your block wants to breath at a 4v rate, and the heads are keeping it back to breathing at a 2v rate, less airflow means less power and could be the prob to your pinging, inadequate airflow would cause improper combustion and thus pinging.

golf4283 · Dec 20, 2003

Can someone explain the difference between 2v heads and 4v heads on mustang blocks?? I thought that there was no difference. I thought 2v and 4v referred to the 2 barrell and 4 barrell carbs. you guys make it sound like they had 4 valve heads, which they didnt. I just want to be clear on the subject. Thanks

dodgestang · Dec 20, 2003

golf4283 said:
Can someone explain the difference between 2v heads and 4v heads on mustang blocks?? I thought that there was no difference. I thought 2v and 4v referred to the 2 barrell and 4 barrell carbs. you guys make it sound like they had 4 valve heads, which they didnt. I just want to be clear on the subject. Thanks

On older 289/302 mustangs there is really no differece between 2v and 4v heads to my knowledge.

On 351c engines there is a HUGE difference though, the ports are very different and the valves are much larger.

D.Hearne · Dec 21, 2003

65fastback2+2 said:
yes, its a performance problem. I only know this from reading loads of posts on the vw site i run, many people try to throw 16v heads on a 8v block. This severly lowers compression. If you take a 8v vw block and put 16v heads on it you get like 7:1 compression. You would do good to get those matching heads on and get everything breathing at the same rate. Right now your block wants to breath at a 4v rate, and the heads are keeping it back to breathing at a 2v rate, less airflow means less power and could be the prob to your pinging, inadequate airflow would cause improper combustion and thus pinging.

What in the wild wild world of sports does comparing VW heads to Ford small block 2 vs 4 bbl heads have to do with the price of eggs? The only difference that the "J" code head had from the 2 bbl head was the size of the combustion chamber. The "J" code head was just a new casting numbered, older 289 head with 53.5 cc chambers. The "2" bbl 302 head had a slightly larger 58 cc chamber. Both had the same ports and valves and any difference in the breathing capabilities was the result of minor casting or machining imperfections.

D.Hearne · Dec 21, 2003

68GEETEE said:
last year I had the heads rebuilt on my '68 302 4bbl. The engine block is the original and it is a J code (4bbl). While the heads were off I took notice of the numbers and found out the the heads are actually off of a '70 motor. Is this ok, since the 70 302 was strictly a 2bbl engine that year? Is it hurting anything, performace, etc? I have had engine pinging problems and am running 93 octane chevron gas, have set the dwell, adjusted the timing, new plugs cap rotor wires, I am wondering if the 2 bbl heads are causing a problem?

P.S. I recently got a pair of '68 4V heads numbers matching for my engine. I just wasnt in a rush to put them on, but I will if they are gonna make a huge difference.

If you have pinging problems, i'd suggest a cam swap , if your motor has a stock cam.What are you setting the initial timing at? putting those "numbers matching" 68 head back on will raise the compression more than what you have now. Are your pistons flattops, dished or domed? I would also ditch the points for a Pertronix unit or any other comparable electronic conversion.Also try running a colder plug.

68GEETEE · Dec 21, 2003

it has a slightly hotter than stock cam, not sure as to the numbers as it was in there when i bought the car two years ago. The car backfired when it had electronic, no doubt poorly installed, I swapped back to points and the backfiring disappeared. The pinging has subsided now that I backed off on the timing, but I still dont think its right.

The timing in itself is a question since she doesnt run good at the factory setting of 6btdc. This is a guess, but I think she is currently around 12btdc. I didnt use a light last time, just backed her up enough to stop the pinging, but she has lost some spunk.

Pistons are flat top.

She does run well overall, its just that darn pinging that bothers me every once in a while. I have Autolite plugs, whatever heat range the book says to use is whats in there now. How does a colder plug help?

D.Hearne · Dec 21, 2003

68GEETEE said:
it has a slightly hotter than stock cam, not sure as to the numbers as it was in there when i bought the car two years ago. The car backfired when it had electronic, no doubt poorly installed, I swapped back to points and the backfiring disappeared. The pinging has subsided now that I backed off on the timing, but I still dont think its right.

The timing in itself is a question since she doesnt run good at the factory setting of 6btdc. This is a guess, but I think she is currently around 12btdc. I didnt use a light last time, just backed her up enough to stop the pinging, but she has lost some spunk.

Pistons are flat top.

She does run well overall, its just that darn pinging that bothers me every once in a while. I have Autolite plugs, whatever heat range the book says to use is whats in there now. How does a colder plug help?

Sometimes a bigger cam profile will allow the motor to run on pump gas , my 68 Mercs 390 is one example, I had another GT390 in a 70 F100 that was the same. Both will run on 87 octane with 10.5 to 1 compression. Very few Fords run good at 6 degrees, all mine are set at 12-14 degrees, makes a huge difference in performance.A colder heat range will also work sometimes in preventing detonation cause the plug tip stays cooler. Check your timing with a light, just guessing isn't a good way to diagnose problems when it comes to engine specs.

68GEETEE · Dec 21, 2003

ok, lets say she runs good at 12 degrees, but she pings, ,then what? Do i then change the plugs to a colder range? How about the thermostat, it has a 190, would a cooler temp like 180 make a difference? Thanks,

Dave

302 coupe · Dec 21, 2003

going to a cooler t-stat will help, see how that does then try cooler plugs.

68GEETEE · Dec 21, 2003

after adjusting the timing this afternoon, i noticed she has a miss at idle. I took some carb cleaner and sprayed around the edge of the manifold, and it almost stalled the engine when i sprayed in one spot. So now I am thinking the manifold wasnt installed right by the guy that did the heads as it seems to have a leak. That would explain the miss, what about the pinging? Can I loosen the manifold bolts and torque them down in the correct order, or do i have to remove it completely?

D.Hearne · Dec 21, 2003

you can try retorqueing the bolts, you got nothing to lose by trying. The colder T-stat may also help in the pinging reduction.

2bbl head on 4bbl engine question

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