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I have a dumb Q



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Old 09-03-2010, 04:13 PM   #1
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I have a dumb Q

Will the heads off my 305 in my 1/2 ton fit the 350 in my 3/4 ton?

I mean bolt on and run perfect...
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Old 09-03-2010, 04:22 PM   #2
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Originally Posted by sho_shane View Post
Will the heads off my 305 in my 1/2 ton fit the 350 in my 3/4 ton?

I mean bolt on and run perfect...
No they will not. You cant just bolt them on and go. If i remember right the heads on a 305 are only 58cc chambers and depending on the year the ones on the 350 will either be 64 or 76 or even 78cc chambers.

So yes they will fit. No it will not run perfect.
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Old 09-03-2010, 04:24 PM   #3
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If you need some 350 heads i have 2 sets of them from a 78 350 that need to be reworked and checked but you can have them if you want.
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Old 09-03-2010, 04:31 PM   #4
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They should work just fine. A reduction in chamber volume equals a boost in compression ratio, all else being equal. This may mean you'll have to run a higher octane fuel, just depending on your combo (cam, etc.).

What are you trying to achieve with this swap?
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Old 09-03-2010, 04:57 PM   #5
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I have a bent valve...

blazer boy send me your number and ill come get them tommrow. And thank you
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Old 09-03-2010, 05:03 PM   #6
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Quote:
Originally Posted by sho_shane View Post
I have a bent valve...

blazer boy send me your number and ill come get them tommrow. And thank you
Sending PM.
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Old 09-03-2010, 06:00 PM   #7
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Yeah I would not use the 305s on the 350. Small ports and valves + raised compression is not the best combination.
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Be careful once you get MUD fever it costs thousands to get rid of it!! LOL
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Old 09-03-2010, 06:54 PM   #8
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Yes they will work, on a stock engine you should have no problem. On a hopped up engine it may cause issues. I did it before and the engine ran great, it was actually mildly builtup as well. 305 heads will have 1.84 intake valve and 58cc chambers while the 350 is 64-76cc and usually 1.96 intake sometime 2.02. SHould be no issue at all if stock.
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Old 09-03-2010, 07:38 PM   #9
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The only DUMB question is a question not asked.
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Old 09-03-2010, 11:13 PM   #10
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The only DUMB question is a question asked by that goat roper snick...
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Old 09-03-2010, 11:17 PM   #11
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Back on topic: Yes, you can make this work. Not work good, but work. We found out the hard way when an engine builder we had put a rebuilt 350 in place of our worn out 305 kept the 350 heads off the 'new' engine and put the 305s on it. It took us a long time to realize what they had done and why the engine wouldn't run any better than it did.
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Old 09-03-2010, 11:30 PM   #12
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yeah, you end up with a 350 with asthma..but would work if you can't afford anything else. City Motor Supply charges $80 bucks a head no matter what they need, I would get the heads offered above and have them go through them, they do all my machine work and so far so good..plus prices are cheap.
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Be careful once you get MUD fever it costs thousands to get rid of it!! LOL
"I got a fever, and the only prescription is more cowbell!"
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Old 09-05-2010, 08:39 PM   #13
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i threw some 305 heads on my 350 i had a few years back and from i can remember it just gave the exhaust a hottor note, no real performance differences
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Old 09-08-2010, 11:05 AM   #14
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Smaller valves are not always a bad thing. It depends on the purpose of the build (the reason I asked the question above).

Smaller ports/valves = higher velocity = more low-end torque (all else being equal).

This, of course, comes with the sacrifice of top-end power. If you plan for the motor to spend the majority of it's life at fairly low RPM (where big torque is more desired), then you won't see any benefit to building a high horsepower, high RPM screamer. In fact, this will sacrifice the low-end power. Low-end torque gives you more power in the lower RPM band where it's needed for some applications.

As with anything, building the right engine combo always comes with compromises. That's why it's improtant to define your goals and build a setup that works well for the intended purpose.
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Old 09-08-2010, 05:18 PM   #15
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Yeah great off idle torque but no ponies..
150 HP 350s
Motors that just run outta breath before you ever get there are disappointing to me. For climbing rocks it would maybe be ok.
Just my opinion. I come from a drag racing background so I am biased.
I have read that some 305 heads are better than other tho.. some googling shows that 416s are the way to go. What castings do you have?
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Quote:
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Be careful once you get MUD fever it costs thousands to get rid of it!! LOL
"I got a fever, and the only prescription is more cowbell!"
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Old 09-09-2010, 09:34 AM   #16
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I'm not disagreeing with you, I'm just saying that you need to pay attention where you're making your power (RPM range and shape of curve), not just the peak power at high RPM.

CFM demands increase with RPM. If you allow your engine to breathe better by opening up the ports and make gobs more power at 6000+ RPM, but you have sacrificed low-end power from idle to ~3000 (let's say), then you could be (depending on the application) shooting yourself in the foot.

If building a tow rig, would you install a cam that didn't make power until 3000 RPM? Sure it may pull all the way to 7000, but that's not really the point for the application. The same goes for choosing a carb. There's no reason to slap a 950cfm Holley DP on a small block that doesn't regularly see over 4000RPM. Use a 650 or so and gain some low-end and perhaps sacrifice ~10hp up top.

I'm not sure how poorly these 305 castings in question will flow. They may be so restrictive that nothing is gained anywhere compared to a 350 head. I was mainly just responding to the blanket statement that small ports and high compression aren't a good thing. That's just not always the case. That's the reason 4 valve heads will outperform 2 valve heads (of equal cross-sectional area) on the low-end. It's due to velocity.
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