stock 305 heads max lift - The 1947 - Present Chevrolet & GMC Truck Message Board Network

60ratrod · 07-15-2009, 08:00 PM

i was wondering what the max lift on a stock 305 head was?? cause i have already changed out the springs, locks and retainers to the ones listed as required/recommended for the comp cams xe268h. will i need to take them in to get machined for more lift or should i be fine?

Chevypoor · 07-16-2009, 07:20 PM

You need to measure this clearance. With valve springs off (exhaust and intake on #1) install the valves. Then install the valve seals. It helps to have a valve spring micrometer as it makes this alot easier. If you are carefull you can hold the valve tight on the seat while holding the retainer and the valve locks up in their groove. Now measure with a small rule the distance from the valve seat to the bottom of the retainer. Take the retainer off the valve and measure the how far the valve lock pocket projects below the bottom of the keeper. Measure the distance from the spring pocket to the top of the valve spring seal. Now add these last two measurements and then subtract this number from the distance from the valve spring pocket to the bottom of the retainer. This is your clearance from the valve seal at zero lift. Multply your rocker ratio times the gross lobe lift on your cam card. This your max valve lift. Subtract your max valve lift from your zero clearance. If you have atleast .070 left you are good. If not then you need to have your guides turned down until you achieve .070 clearance.

purewhitemp5 · 07-16-2009, 07:51 PM

The machine shop said with stock springs the max I could do was .480 with 305 heads.

60ratrod · 07-16-2009, 08:42 PM

well if 100% stock lift is .480, then i should be sittin pretty since i have swapped out to comp 981 springs(recommended/required for the xe 268h), but since i still have yet to install the springs on the other head then i'll do the measurements just to be safe. i gotta go to the LPH anyway to get some other items so i'll see if they have a micrometer and all that. i gotta get some easy outs since i found a broken bolt in one of the end exhaust bolt holes

Chevypoor · 07-17-2009, 05:36 AM

The clearance of .070 is without the seal. With the seal I believe it is .040. Sorry about that... brain fart!

07-16-2009, 07:20 PM	#2
Chevypoor Registered User Join Date: Jul 2008 Location: Richmond, VA Posts: 56	Re: stock 305 heads max lift You need to measure this clearance. With valve springs off (exhaust and intake on #1) install the valves. Then install the valve seals. It helps to have a valve spring micrometer as it makes this alot easier. If you are carefull you can hold the valve tight on the seat while holding the retainer and the valve locks up in their groove. Now measure with a small rule the distance from the valve seat to the bottom of the retainer. Take the retainer off the valve and measure the how far the valve lock pocket projects below the bottom of the keeper. Measure the distance from the spring pocket to the top of the valve spring seal. Now add these last two measurements and then subtract this number from the distance from the valve spring pocket to the bottom of the retainer. This is your clearance from the valve seal at zero lift. Multply your rocker ratio times the gross lobe lift on your cam card. This your max valve lift. Subtract your max valve lift from your zero clearance. If you have atleast .070 left you are good. If not then you need to have your guides turned down until you achieve .070 clearance. __________________ 1990 S10 Reg. cab 2wd 2.5/ 700r4, lowered, soon to be a TBI 350/ 700r4 1993 2500 Reg. cab 4wd 6.5 turbo diesel/ 5spd, bigger turbo, Bull Moose pump, cold air intake, and a few other mods 1969 C10 Reg. cab 2wd 305/350, RHS heads, Voodoo Cam, Gilmer drive, 2400 stall, and lots of other goodies!

07-16-2009, 07:51 PM	#3
purewhitemp5 Registered User Join Date: Jun 2009 Location: Bear Delaware Posts: 72	Re: stock 305 heads max lift The machine shop said with stock springs the max I could do was .480 with 305 heads.

07-16-2009, 08:42 PM	#4
60ratrod yes, i do Join Date: Jun 2007 Location: Spokane, wa Posts: 2,734	Re: stock 305 heads max lift well if 100% stock lift is .480, then i should be sittin pretty since i have swapped out to comp 981 springs(recommended/required for the xe 268h), but since i still have yet to install the springs on the other head then i'll do the measurements just to be safe. i gotta go to the LPH anyway to get some other items so i'll see if they have a micrometer and all that. i gotta get some easy outs since i found a broken bolt in one of the end exhaust bolt holes __________________ ERROR 404....... SNAPPY COMEBACK NOT FOUND _______________________________________________________________________________________________ -60 Chevy C10, dead 350/good th350 combo, sitting on a 76 c10 blazer frame, built from 11 different vehicles "the abomination" -07 gmt900 silverado 1500 lt xcab z71, granite blue -81 suzuki gs650g "shelah"- current project -81 kz1000m1 csr "sarge" -next project (just beautification) -07 kawasaki vulcan classic vn900

07-17-2009, 05:36 AM	#5
Chevypoor Registered User Join Date: Jul 2008 Location: Richmond, VA Posts: 56	Re: stock 305 heads max lift The clearance of .070 is without the seal. With the seal I believe it is .040. Sorry about that... brain fart! __________________ 1990 S10 Reg. cab 2wd 2.5/ 700r4, lowered, soon to be a TBI 350/ 700r4 1993 2500 Reg. cab 4wd 6.5 turbo diesel/ 5spd, bigger turbo, Bull Moose pump, cold air intake, and a few other mods 1969 C10 Reg. cab 2wd 305/350, RHS heads, Voodoo Cam, Gilmer drive, 2400 stall, and lots of other goodies!

07-15-2009, 08:00 PM	#1
60ratrod yes, i do Join Date: Jun 2007 Location: Spokane, wa Posts: 2,734	stock 305 heads max lift i was wondering what the max lift on a stock 305 head was?? cause i have already changed out the springs, locks and retainers to the ones listed as required/recommended for the comp cams xe268h. will i need to take them in to get machined for more lift or should i be fine? __________________ ERROR 404....... SNAPPY COMEBACK NOT FOUND _______________________________________________________________________________________________ -60 Chevy C10, dead 350/good th350 combo, sitting on a 76 c10 blazer frame, built from 11 different vehicles "the abomination" -07 gmt900 silverado 1500 lt xcab z71, granite blue -81 suzuki gs650g "shelah"- current project -81 kz1000m1 csr "sarge" -next project (just beautification) -07 kawasaki vulcan classic vn900



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