surprise at the machine shop - The 1947 - Present Chevrolet & GMC Truck Message Board Network

NYC-10 · 12-22-2008, 04:55 PM

sent my heads to the machine shop and it turns out they are 307 heads.My block is a 350.Was it common practice to put smaller heads on a 350?Turns out my friend has a set of 350 heads so I will use them instead.

dwcsr · 12-22-2008, 04:59 PM

it depends. Some have a smaller chamber increasing the compression. 305's on a 350 is a common swap.

**special-K** · 12-22-2008, 05:33 PM

What size valves and what cc were they?

72armyswbtruck · 12-22-2008, 09:37 PM

Not super uncommon for their to be 307 heads on a 350, look at the harmonic balancer. You might be suprised there as well.
But they have definitely been swapped out at sometime.

NYC-10 · 12-22-2008, 09:40 PM

Quote:

Originally Posted by 72armyswbtruck

Not super uncommon for their to be 307 heads on a 350, look at the harmonic balancer. You might be suprised there as well.
But they have definitely been swapped out at sometime.

you think they would swap that as well?I'll have to look tomorrow

jholley · 12-22-2008, 09:51 PM

Depending on what casting your 350 heads are you may be better off with the 307 heads. The combustion chambers are most certainly smaller boosting your compression ratio a bit.

NYC-10 · 12-22-2008, 10:01 PM

the casting on the 350 heads are 387 3487

66skylarkpost · 12-22-2008, 10:04 PM

the draw back to putting on smaller cid heads are that they typically have smaller valves to clear the cylinder walls and thus smaller ports to maintain velocity

NYC-10 · 12-22-2008, 10:30 PM

block is a 350 I checked the numbers and measured the pistons-It has flat top pistons with a valve relief

chevybuldr · 12-22-2008, 10:03 PM

Are your pistons flat or dished? If they are dished I would stay with the 307 heads. Keep the compression up there. Are you sure that the motor is a 350? Check the casting number in the back while the heads are off.

1966gmc · 12-22-2008, 11:12 PM

Put some 350 heads on it and you will love yourself.

12-22-2008, 04:55 PM	#1
NYC-10 screamin eagle Join Date: Oct 2007 Location: westbury ny Posts: 237	surprise at the machine shop sent my heads to the machine shop and it turns out they are 307 heads.My block is a 350.Was it common practice to put smaller heads on a 350?Turns out my friend has a set of 350 heads so I will use them instead. __________________ SCREAMIN EAGLE

12-22-2008, 04:59 PM	#2
dwcsr Hollister Road Co. Join Date: Apr 2005 Location: Houston Posts: 6,134	Re: surprise at the machine shop it depends. Some have a smaller chamber increasing the compression. 305's on a 350 is a common swap.

12-22-2008, 05:33 PM	#3
special-K Special Order Join Date: Nov 2004 Location: Mt Airy, MD Posts: 85,861	Re: surprise at the machine shop What size valves and what cc were they? __________________ "BUILDING A BETTER WAY TO SERVE THE USA"......67/72......"The New Breed" GMC '67 C1500 Wideside Super Custom SWB: 327/M22/3.42 posi.........."The '67" (project) GMC '72 K2500 Wideside Sierra Custom Camper: 350/TH350/4.10 Power-Lok..."The '72" (rolling) Tim "Don't call me a redneck. I'm a rough cut country gentleman" R.I.P. ~ East Side Low Life ~ El Jay ~ 72BLUZ ~ Fasteddie69 ~ Ron586 ~ 67ChevyRedneck ~ Grumpy Old Man ~

12-22-2008, 09:37 PM	#4
72armyswbtruck Registered User Join Date: Feb 2004 Location: Idaho Posts: 4,034	Re: surprise at the machine shop Not super uncommon for their to be 307 heads on a 350, look at the harmonic balancer. You might be suprised there as well. But they have definitely been swapped out at sometime. __________________ "Remember, They can Kill You, but they can't eat You, That's against the law!!!!!!!!!"

12-22-2008, 09:51 PM	#6
jholley Registered User Join Date: Jul 2008 Location: TX Posts: 737	Re: surprise at the machine shop Depending on what casting your 350 heads are you may be better off with the 307 heads. The combustion chambers are most certainly smaller boosting your compression ratio a bit. __________________ ------------------------------------------------- Jim Garage fillers... 85 Chevy C10 Silverado LWB 07 Nissan Altima 2006 Mini Cooper S

12-22-2008, 10:01 PM	#7
NYC-10 screamin eagle Join Date: Oct 2007 Location: westbury ny Posts: 237	Re: surprise at the machine shop the casting on the 350 heads are 387 3487 __________________ SCREAMIN EAGLE

12-22-2008, 10:04 PM	#8
66skylarkpost Registered User Join Date: Mar 2006 Location: kearney,nebraska Posts: 443	Re: surprise at the machine shop the draw back to putting on smaller cid heads are that they typically have smaller valves to clear the cylinder walls and thus smaller ports to maintain velocity __________________ '70 k-10 longbox- mid 70's drivetrain 350/350 487x heads 10.1:1 flowmasters ,35's 3.73's auburn posi ,rear shackle flip. '72 short stepside U.S. forestry truck, '73 455 buick,400 turbo,dropped 2"-4 1/4" ,3.07 posi,:'89 silverado 1500 ,OK truck ,5.7 holley tbi ,trick 700r4 3.07 auburn posi ,and my '66 skylark ,'73 centurion and my '84 monte carlo imca stock car

12-22-2008, 10:30 PM	#9
NYC-10 screamin eagle Join Date: Oct 2007 Location: westbury ny Posts: 237	Re: surprise at the machine shop block is a 350 I checked the numbers and measured the pistons-It has flat top pistons with a valve relief __________________ SCREAMIN EAGLE

12-22-2008, 10:03 PM	#10
chevybuldr Registered User Join Date: Oct 2008 Location: Livermore ca Posts: 699	Re: surprise at the machine shop Are your pistons flat or dished? If they are dished I would stay with the 307 heads. Keep the compression up there. Are you sure that the motor is a 350? Check the casting number in the back while the heads are off.

12-22-2008, 11:12 PM	#11
1966gmc Why does it taste purple? Join Date: Sep 2007 Location: Cambridge Md Posts: 621	Re: surprise at the machine shop Put some 350 heads on it and you will love yourself.



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