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Old 05-21-2007, 04:57 PM
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hi everyone just wanted to pick everyones brain that is willing to have ut picked. i just finished restoring a 1967 impala for my daughter. i installed a 60 over 350 with 305 heads. the valves are not the 195 but around the 175 range.i did run a diegrinder and smooth out the ports both intake and exaust. also took the sharp edges of the casting around the chamber i put a performer rpm intake and cam shaft in the motor with a 600 edlebrock carb. i am not sure what the compression ratio of the engine is or the fresh reman botom end was that o bought. the problem i am having it is just dead. it sounds great at an idle i have played with timing but it pings as soon as you get into it at any rpm. it stops pinging with a base of 0 and a total of 30 but with the setting there it is a total dog i bumped octain thinking it would help. it did a little but still dead and pinging. it is infront of the original 2 speed glide.i have never had a glide before and my last build was a 13 second 454 in a 1980 truck. it worked well. i think honestly the way it pulls now id been better off with a stock 4 cyl..... any sugestions? also the cam is degreed at zero. i dont want or expect it to run 10s but something would be nice. it has a hei replacment msd billet dist.. thanks and hope you can help..

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Old 05-21-2007, 06:03 PM
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Quote:
Originally Posted by billlt583
hi everyone just wanted to pick everyones brain that is willing to have ut picked. i just finished restoring a 1967 impala for my daughter. i installed a 60 over 350 with 305 heads. the valves are not the 195 but around the 175 range.i did run a diegrinder and smooth out the ports both intake and exaust. also took the sharp edges of the casting around the chamber i put a performer rpm intake and cam shaft in the motor with a 600 edlebrock carb. i am not sure what the compression ratio of the engine is or the fresh reman botom end was that o bought. the problem i am having it is just dead. it sounds great at an idle i have played with timing but it pings as soon as you get into it at any rpm. it stops pinging with a base of 0 and a total of 30 but with the setting there it is a total dog i bumped octain thinking it would help. it did a little but still dead and pinging. it is infront of the original 2 speed glide.i have never had a glide before and my last build was a 13 second 454 in a 1980 truck. it worked well. i think honestly the way it pulls now id been better off with a stock 4 cyl..... any sugestions? also the cam is degreed at zero. i dont want or expect it to run 10s but something would be nice. it has a hei replacment msd billet dist.. thanks and hope you can help..
Yeah dyno-mite, 305 heads on a 350 have shot the compression to the stars. Now that's not to say there aren't other issues, but you can count on this one.

You need to go back and look at the static compression ratio which means you need to know the thickness of the head gasket so you can compute it's volume this also applies to the clearance, if any, between the piston crown and the block's head deck. Chamber size of the heads, 305s run around 53 to 58 cc, and the volume of the piston's dish if it has one. The static compression is the sum of these divided into the sum of these plus cylinder displacement. If you're getting up over 9 to one, you've got trouble.

Your choices range from replacing the heads with something with bigger chambers to playing with head gasket thicknesses. GM gaskets can be had from steel shims at.020 or so to composition at .058 inch. With a cast iron block and head, gaskets can be stacked and composition can be mixed with steel shim to dial the thickness in. This isn't the best solution technically but it's the cheapest. The best solution would be "D" dish pistons with the dish selected for the head volume to get around 9 to one on a shim gasket.

Bogie
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Old 05-21-2007, 06:23 PM
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Yep, those small chamber small valve 305 heads are really a killer on a 350. Like was stated, the compression is now most likely way too high for pump gas. Zero timing will kill off any performance too. Any stock/modest 350 can use 10-15 initial and up to 36-40 total, not counting the vac advance.

Do you know what piston went into the build? Dish, 2 valve flat top, 4 valve flat top? Was the block decked or still at stock height? This info will help us figure where the compression ended up.

Mark
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Old 05-21-2007, 06:45 PM
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I agree that the biggest, but not only, problem is the heads. The LT1 in my 95 Z28 is rated at 10.5-1 with the stock 58cc chamber. So you can see there is a compression issue to deal with. There are special pistons made for a 350 to use 305 heads.
Another item you need to look at is the cam. If I read your post correctly, you are using the Performer RPM intake and cam. That is a lot of cam and intake for a heavy car with a Powerglide. You didn't mention stall speed on the converter or rear gears.
I used to have a 67 Impala conv. that had a 327. I rebuilt the engine stock with the exception of the camshaft and intake. I used a short duration, high lift cam with 108 of lobe separation and a Performer intake. The carb was the stock Q-jet. The trans was a T-350 with a 11" converter. The rear gear was a 3.08.
The engine had a nice lopey idle and would light the rear tires for quite a distance from a dead stop. Mileage was good at around 16 around town and about 19 on the highway if memory serves me correctly.
It appears to be an issue of some mis-matched components. The worst of which is the heads. Invest in some Vortec heads, a smaller cam and a stall converter. You won't believe the difference.

Barry
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Old 05-21-2007, 07:11 PM
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What is the casting number on the 305 heads? Should have gone with 1.94" valves and some chamber deshrouding. A performer rpm cam is a high rpm cam. Does not get busy until after 3000rpm. You want a 3500 stall and 4.10's or 4.56 gears for a 67 Impala. You must recurve the stock distributor to limit the mechanical advance travel. This will allow much more intial timing (20 to 24deg BTC) at idle but the same power optimum 32 to 36deg at high rpm. Try "locking out" the distributor mechanical advance ( remove the weights and springs and bind the advance mechanism) and set the base timing at 32deg BTC. Run "cooler" performance oriented heat range non projected tip Champion RV8C spark plugs plugs gapped at .035". Restrict vacuum advance to about 10-12deg at high cruise. (most stock distributors have 20deg vaccuum advance and 22 to 24deg mechanicial advance travel.( {too much mechanical travel and too much vacuum advance} Restricting the advance travel will allow much more timing at idle with much better low end response. without over advanced top end and pinging.
A Performer RPM cam needs this modified spark advance curve , very high stall converter (10" 3500stall) and high rear gear ratio (4.10 or 4.56:1) to work right. No , this is not too much.

If you do not want to change the converter and rear gearing to match the RPM cam, Then change the cam to match your stock glide converter and rear gear ratio. Something with a .050" duration of between 210 and 218 is good.
You will need the highest available octane pump premimum gas.

Some of the 305 heads have good performance potential (when properly modified) but will need large valves (1.94x 1.60" for a 350) and full porting. A few minutes spent with a die grinder is not enough. Some of them are not really worth working with for high performance. You'll never realise the power you want with the RPM cam and manifold unless you get the cylinder head flow up.
Which heads do you have? The casting number is found under the valve covers. Flat top pistons?
If your 600 Edelbrock is the mileage oriented model with the lean primary jetting and electric choke you can re-jet it richer more like the performance oriented model carb with a manual choke. This will also reduce the tendancy to ping at WOT.

Last edited by F-BIRD'88; 05-21-2007 at 07:19 PM.
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Old 05-28-2007, 10:37 PM
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wich head??

hey gang..they are flat top pistons. these are the cam specs..part num#12-246-3 int..first exaust second..adv dur:274 int 286 exh dur@ .50...230 intake 236 exaust lobe seperation 110.0 valve lift .49 .49 i am getting the idea i had a bad choice in cylinder heads. that is ok.. what i am looking for is drivability i am putting lots of miles on the car.. and long trips.. we all know what fuel costs and its more in canada at least hear. any recomendations on heads. i dont want a race car but i also cant have my chrysler parteners cuda beeting on me either... any ideas.. please help chevy guys? edelbrock? valve size? cc? any input would be greatly appriciated.. i know rite now he would crush me and he uses his for the same purpose..thanks also of course cheeper is better and i am not aposed to cast iron..

Last edited by billlt583; 05-28-2007 at 10:44 PM.
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Old 05-29-2007, 05:58 AM
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Do a compression test and let us know what kind of psi she is pumping, I really think you can make this combo work as is but we need to find out what the problem is. What spark plugs are in it now? Try some R42T AC plugs and run premium and also recurve that timing if need be. It should want about 15 degrees initial with a total of 38ish. Disconnect the vacume advance for now untill the ping is gone then add it a little at a time on a ported source-the MSD distributor should have an adjustable vacume diaphram I think.
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Old 05-29-2007, 09:19 AM
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Your combinstaio is severly mismatched. It will neither get good fuel mileage or beat anything in a race.
Your cr could be as high as 11.25:1 (53cc head) It will always ping unless you severly retard the timing or run high octane racing fuel. If the heads have the small 1.72" valves you're never going to make any power.

Changing to a high flow 64cc head will get you the power and tame the cr.
Vortec heads are the cheap way to go fast.

A powerglide trans just does not have enough low gear ratio to make a heavy Impala move off the start. When combined with a stock rear gear ratio and stock stall converter off the line acceleration is pretty soft. using a large cam like the XE274 just makes it worse. The XE274 startes to get busy around 2800rpm. use a 2800stall (11" converer) and 4.10's.
Unless you are willing to change the rear gear ratio and converter stall, change the camshaft.
Comp #12-234-2 XE256-10 is a good match for a stock stall PG and stock gearing (likely 2.73 or 3.08's).
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Old 05-29-2007, 02:34 PM
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Quote:
Originally Posted by F-BIRD'88
Your combinstaio is severly mismatched. It will neither get good fuel mileage or beat anything in a race.
Your cr could be as high as 11.25:1 (53cc head) It will always ping unless you severly retard the timing or run high octane racing fuel. If the heads have the small 1.72" valves you're never going to make any power.

Changing to a high flow 64cc head will get you the power and tame the cr.
Vortec heads are the cheap way to go fast.

A powerglide trans just does not have enough low gear ratio to make a heavy Impala move off the start. When combined with a stock rear gear ratio and stock stall converter off the line acceleration is pretty soft. using a large cam like the XE274 just makes it worse. The XE274 startes to get busy around 2800rpm. use a 2800stall (11" converer) and 4.10's.
Unless you are willing to change the rear gear ratio and converter stall, change the camshaft.
Comp #12-234-2 XE256-10 is a good match for a stock stall PG and stock gearing (likely 2.73 or 3.08's).
Good advice....well said
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Old 05-30-2007, 02:03 AM
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hey gang. first off thanks for all the help. i bought a set of 400 heads from a local racer. they have 195 and 150 valves with extencive porting. they looked great. he said try them. well i bolted them on here tonight. they have a 72 cc chamber. i got to say in the shop the throttle responce is better and the power has increased but the builder said they could handle the lift. but after 3 trys and trying to get the rocker noise out i am guessing they are stacking the springs. i want to rip my hair out. i have a line on a set of ported and polished edelbrock rpm 202 150 heads. with 64cc chambers. good idea? bad idea? also a 2500 stall converter is on order. the gears are 336 weard i know but after the division thats the figure. i expect the low end lag and expected it. do you think the rpm heads are what i need? or should i just change the springs and run these ones i have?
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Old 05-31-2007, 10:52 AM
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cant win!!

hey gang back again. the top end noise that i stated is only there when the engine is up to operating temp.. i have tried several adjustments. but still there.. any ideas?
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Old 05-31-2007, 03:01 PM
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If you got those ported heads from a "racer" and they have racing springs ( intended for a race cam) they may have too much spring pressure causing the hyd lifters, internal plunger to collapse. You would notice this the most when the motor is hot and the oil pressure is lowest at idle.
A hyd lifter can only withstand about 125 to 135lbs seat pressure and about 350lbs over the nose. Anything more is way too much.
Are the rocker studs "drilled and pined" or screwin type. Could have pulled the rocker studs. Could have wrecked the cam and lifter with all the idleing if it is or was fresh and the cam is not broken in yet.
You need to remove an valve spring and check its installed height, open height, coil bind height and the spring pressure while seated and open.
You also need to check the space between the valve spring retainer bottom and the valve guide top or valve seal.
The Edelbrock RPM heads work very well. You can make good power with them. If they were ported properly they can really rock.
Why did you order a "2500stall" when the cam you have needs a 3000+ stall?
A 3.36:1 ratio is a GM ratio, Nothing weird, Your math is right. You need 4.10's or 4.56's (to beat any one in a drag race with that heavy car). The fact that you have a PG trans with a limited ratio first gear (1.76:1)makes the need for the proper rear gear (4.10) and converter stall (3000 to 3500) even more critical. A 3speed auto trans would be much better. (still needs a 10" converter and gear with that cam.
if you did in fact encounter a spring coil bind stack or the retainers crashed the guide tops, your pushrods will likely be bent. make it real difficult to adjust the valves....

Last edited by F-BIRD'88; 05-31-2007 at 03:28 PM.
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