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Old 09-10-2003, 09:53 AM
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350 build

I am trying to build a Chevy 350 and got a bunch of parts from a friend that I don't know will all work together. The block is bored .040 over but with rust damage on two of the cylinders so I am thinking of taking it to .060 over. The heads are 376450 that are meant for a 305. A carter AFB 625cfm that needs rebuild. And pistons that are flat top that if I bore out that I will have to replace anyway. I am looking for a 9.0 or greater comp ratio because the engine is going into a 81 GMC Jimmy. Can anyone help?

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Old 09-10-2003, 10:20 AM
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Hi Scotty, another phx person! LOL

Sounds like a real hodgepodge of stuff. Probably the best suggestion I can make is to find a good machine shop and have them look at the block, crank, pistons and heads. Trying to give advise without seeing the parts is going to be tough.

I'm in the process of building another 350 for my '77 truck and found a great machine shop here in Sunnyslope that has kept up with all the new technology and building info. I"m building a 30 over 350, stock crank and rods, but I had a set of 882 heads that they bored out the intakes to take the 1.94 valves. I had stainless valves put in and good seals. I"m also having them set the "quince" distance on the block height so I can run 87 octane on 9.3 pistons. Plus a good Crane cam and lifters and full roller rockers. Its basically just a good torque motor that should last another 150k in the old beast. I'm on engine number 2 and have 328,000 miles on the truck. If you like, send me an email and I'll send ya my phone number and we can chat.

Mark
Jacobsenx3@aol.com
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Old 09-10-2003, 10:31 AM
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JMARK,

do you know what's involved with modifying the heads to accept bigger valves? Do they just enlarge the seats, or are the seats replaced with bigger ones?

oh yeah, and how much did that operation run you (if you don't mind sharing).
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Old 09-10-2003, 11:52 AM
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Good morning "unstable"

Changine the valve size is quite simple for a machine shop. On my heads, they were the '882 castings from '76. They had 1.72 intakes and 1.5 exhaust. The exhaust valve size I left alone and they already had good hardened seats.

I wanted to move up to the 1.94 intakes and ended up buying a new set of PEP full stainless intake and exhaust valves on eBay for under 60 bucks. ( same brand the shop uses too, at half the price, shop owner was pissed but thats a different topic i'm going to post.)

Anyway, all they do is measure the outer most machined surface of the valve, then cut the new seating surface in the head. ( Intakes don't have a replacable seat.) After the seat surface is machined, they then bore out the remainder of the head to match the newer diameter. Its pretty slick.

The labor/machining cost for the enlarging of the intakes was $80. Total price that I have in the heads is $380. They milled them .005 to get them flat, installed all new guides and also installed positive seals.

They have my block now and am waiting on the machine work so I can start assmbly. I'm using Speed Pro Hyperutectic teflon coated postons with a beginning comp ratio of 8.8 so after they deck the block to set the quinch distance, I should end up around 9.1 to 9.2. I don't want to run premium! LOL
Crane 278 cam, lifters and full roller rockers.
I'm dropping my Performer intake and AFB and going back to the stock intake, and brand new Q-jet ( $76 on eBay too! LOL), headers and hope for another 150,000 on this engine.

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Old 09-10-2003, 01:45 PM
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If you don't mind me asking Jmark, why are you going back to a stock intake and carb?
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1984 Pontiac Grand Prix
-350 4-bolt main
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Old 09-10-2003, 02:06 PM
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Well, I never noticed any difference when I put on the intake and AFB. Its now 13 years old and never been rebuilt. I"ve always liked the Q-jet and 3 machine shops here all recommend the Q-jet and stock manifold for good torque. I"ll probably clean up the AFB and dip the manifold and then bag it all up so I can try it again if I want.
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Old 09-10-2003, 07:52 PM
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I thought that intake seats could and HAVE TO BE REPLACED if you get a real old casting from like 1970 when they used leaded gas?

Thanks for all the info. Looks like you are going to have a little fun with that puppy.
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Old 09-10-2003, 10:11 PM
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Well, I too thought that the intakes had seats. But they said no, only the exhaust valves had replaceable seats. If you get somewhere before '74 heads, the exhaust seats are not hardened. But with the higher exhaust temps and no more lead, the seats on the later heads have to be hardened. The intake valves run pretty cool because they are bringing in outside are all the time.
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Old 09-11-2003, 09:09 AM
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well perhaps the intake seats aren't "removeable", but are often opened up to install hardened seats.

http://www.inlinepages.com/~inlinefe...fications.html

Quote:
4.) Installing larger intake valves.

This is a fairly inexpensive modification that youre machinist can perform when you take the head back in for a 3 angle valve job and any valve guide work that you might need to have done.

The 1966-1977 heads all have a 1.64" intake valve and a 1.49" exhaust valve and a non hardened valve seats (for leaded gas) while the 1977-1983 heads had 1.75" intake valves and 1.49" exhaust valves and a hardened valve seats for unleaded gas.

So what you want to do is to have your machinist cut the seats open larger and install the later model 1.75" intake valves in the earlier heads.
Obviously if you have the 78-83 head you can skip right over this part of the page.

not trying to be argumentative. just trying to get the facts straight for myself...and learn as much as possible

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Old 09-11-2003, 09:34 AM
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Thanks for the post Jmark, however I do have another question. The Jimmy has a straight 6 and a 3 speed tranny, will the 350 bolt up or will I need to go with a sm465 4 speed? If so, any good wrecking yards in Phoenix area that might have a sm465 mated to a np205?
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Old 09-11-2003, 10:08 AM
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Unstable..

That quote you posted was from a 6 cyl article. I don't know much about the 6, but the V8s must be different. The smallest V8 intake valve that I"ve ever seen is the 1.76, then the 1.94 and lastly is the 2.02. I"ve seen some larger aftermarket intake valves, but I don't know how they fit them in without hitting the exhaust valve. They came in either a 1.5 or 1.6.

As far as "intake seats", from what the machine shop says, the intakes on the V8 don't have replacable seats, unless you specifically machine for them and install em. All they do is machine the valve seating surface right into the head. The cast iron is fine for the intakes, doesn't get that hot.
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Old 09-11-2003, 04:05 PM
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Scotty, You can`t use your 305 heads on your 350. Well you can but your compression ratio will be toooo high , probably 11.0 or so. There would be more involved. The 305 heads are either 55 or 58 cc`s. Your 350 probably came with 76 cc heads. I`m running 64 cc heads and have a 9:7.1 compression ratio. Your head gaskets and pistons will play with your compression also. I would for performance go with a after market head, it`s worth 100 HP. or for the street get rebuilt heads for about $250 and trade the 305 in. Good Luck.
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Old 09-11-2003, 04:34 PM
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Keith makes a good point, but in your case those heads have a 76cc chamber. They should have a 1.72 intake and 1.5 exhaust, pretty standard head. They were used from '75 to 81 on the 262/267/305. ( did chevy actually make a 262 or a 267? LOL)

With a valve change, if you want to, they should make a good stock head.

If you want something really good and affordable, ck out the Top Proline "torker" heads on Ebay. A pair complete with stainless valves and positive seals and pioneer high lift compatable springs are going for under $600. I spent almost $400 on my last set of fairly stock heads, wish I'd seen the torker heads first.

Mark
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Old 09-11-2003, 05:00 PM
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Just to add my two cent's worth,i've gone the 305 route before and for what it's worth,the 305 head's are not worth the money because in stock form they only flow 150cc to 160cc on the intake side.Plus the combustion chamber's are for a 3 3/4 in. bore,and the older 305 head's had 58cc chamber's and the latter one's had 60cc chamber's,witch had i beleive 172 or 174 intake valve's plus the 150 exh valve.I had a set of 305 head's with 60cc chamber's,and had 194 intake valve's installed and placed the intake valve to close to the chamber wall witch shrouded the valve and would mess up the intake flow. (just my two cent's)

Just to add my two cent's worth,i've gone the 305 route before and for what it's worth,the 305 head's are not worth the money because in stock form they only flow 150cc to 160cc on the intake side.Plus the combustion chamber's are for a 3 3/4 in. bore,and the older 305 head's had 58cc chamber's and the latter one's had 60cc chamber's,witch had i beleive 172 or 174 intake valve's plus the 150 exh valve.I had a set of 305 head's with 60cc chamber's,and had 194 intake valve's installed and placed the intake valve to close to the chamber wall witch shrouded the valve and would mess up the intake flow. (just my two cent's)

Last edited by bowtieorbust; 09-11-2003 at 05:00 PM.
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Old 09-11-2003, 05:28 PM
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I have never seen factory removable valve seats in anything but aluminum head. Most hardened exhaust valve seats in cast iron heads are flamed hardened and yes the intakes run cool engine that it does not require them. When hardened exhaust valve seats are installed the cast iron seat it cut out and a hardened one put in. If not done well it can wreak havoc with the flow of the head and there is some question as to weather it even is necessary anyway.
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