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L31 350 Vortec swap/rebuild Hey TGO! I started my L31 350 Vortec rebuild and swap for my 85' firebird. This is my first engine swap and rebuild, I will be posting lots of pics and info as i go along, I will probably have some questions along the way as well. For this build I wanted to try to get to 350hp with the OEM vortec heads (12558062) and a new cam and valve train. I am prepared to do a complete rebuild, however, if I can save some $$ without machining and keeping as many parts as I can from the stock engine, that would be preferred. I basically copied similar vortec builds that claim to make 350-380hp. LT4 Hot cam 218/228 .492/.492 lift, edelbrock performer RPM intake, would like to be in the 650 cfm range for a carb, not sure if holley or edelbrock is better. Im running a q-jet on the stock 5.0L and alot of people say they are finicky but I had no troubles tuning it, probably wont keep it because I want to sell the 5.0L complete and running. I have done research on this build and apparently you DO NOT need to machine the heads to run 1.6 roller rockers (to maximize the LT4 hot cam performance) if you use 26915 or 26918 comp beehive's, comp 787 retainers and 648 keepers. This package including the cam should be about 550$ new parts. Does anyone have experience running this combo without machining? pics coming up.. |
Re: L31 350 Vortec swap/rebuild |
Re: L31 350 Vortec swap/rebuild https://cimg3.ibsrv.net/gimg/www.thi...3228af6f48.jpg I guess the last owner thought he could fix his broken spark plug wire with tuck tape.... :doh: hopefully that was the only thing he touched under the hood haha yikes! |
Re: L31 350 Vortec swap/rebuild Disassembled and ready for cleaning and analysis at the machinist. I sure hope i dont have a dud from the junk yard, although i knew it was a gamble from the junk yard and still alot cheaper than a new crate. https://cimg0.ibsrv.net/gimg/www.thi...22e55409c1.jpg One thing i was thinking of, was taking that stock vortec roller cam, lifters and springs ( with new seals and locks and probably rods to be safe ) and putting it into the original 5.0L LG4. From what i have researched they are interchangeable and should give a little more power to it. It would help me sell it and maybe for a little more $ too. can i use the springs from the original vortec heads on the 5.0 heads, or better yet keep the springs on the 5.0 and just do the cam/lifter swap?? |
Re: L31 350 Vortec swap/rebuild Oh i forgot to write where i got the engine, the engine is from a junk yard 98' GMC 2500. I also have to run an electric fuel pump for this swap, is an in-tank pump the way to go for cooling and longevity? and do i have to alter/replace my tank for the pump to work? |
Re: L31 350 Vortec swap/rebuild It's an '85 305 LG4? If so the roller cam wont fit/work. Chevy didn't go to roller cams until 1987, so your '85 block will not have the lifter bosses machined for the roller lifter "dog bones" (retainers), nor will the cam tunnel be drilled and tapped for the "spider" to bolt down.. Also the front of block will not be machined or tapped for the cam retainer plate. |
Re: L31 350 Vortec swap/rebuild I see, that would be what they call a "roller block" right? I watched that video of your camaro, that thing is mean! How did you get such high compression? If i have to deck the block or even resurface the heads at the machinist, i will lose distance from the top of the piston to the head chamber which would compress the air/fuel into a smaller space, thus adding compression, from what my searches have told me. Another way to increase compression is to go with flat top pistons right? are those the main factors in gaining compression? |
Re: L31 350 Vortec swap/rebuild Correct.. That would be what's known as a Roller block. 1987 up chevy V8. Thanks man. I need to get a new video up of my car. That's with the small exhaust and carb. Since then I have upgraded to 3" dual pipes, X pipe, dynomax ultra flo mufflers, holley 750 DP carb. Compression on mine comes from 2 valve pocket 5cc flat top pistons, 64cc heads, and 4.100" x .015" thick head gaskets. Yes you are correct.. Decking/milling block or heads will reduce the volume of the combustion space, there for giving you more compression. Larger cylinder bore size will increase compression Longer stroke length will increase compression Smaller head combustion chamber volume will increase compression Smaller head gasket bore and thinner head gasket will increase compression Smaller piston volume (flat tops rather than dished, or domes rather than flat tops) will increase compression. With my engine, I have a 355 which is a 350 that's bored .030" over. So my bore is 4.030" Stroke is 3.48 Pistons sits .025" below the deck Flat top 5cc pistons 64cc heads 4.100 x .015 head gaskets Milling/resurfacing heads... Rule of thumb .008" cut = 1cc |
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