Sorry guys – I’m leaning towards rebuilding my 305 on my ’84 trans-am. The pro’s of a 350 don’t necessarily outweigh the cons for me.
https://www.thirdgen.org/forums/engi...rformance.html


I’m going to keep my stock carburetor. The intake manifold depends on the heads. So, from this board and from performance magazines (hate me build), I see these configurations for the heads and cam:


-Vortec heads from a late model 305 and Comp XE268H flat-tappet hydraulic cam.

-Trick Flow Super 23 heads with 56cc combustion and Comp XM270HR hydraulic roller tappet cam.

-World Products 305 S/R Torquer heads with Comp XE262H-10 flat-tappet hydraulic cam.

-Vortec Heads with 26918 compcam valve springs and Comp XR264HR-12 hydraulic roller tappet cam.

-L98 350 aluminum corvette heads


Those that know, what combination do you suggest? I’m 2 months away from addressing the engine. I’m working on the suspension now. Drivability and smooth idle are important to me.

 

I have an '87 roller cam 305 at the machine shop right now. It's getting Speed Pro H534CP flat tops and I'm using the XR264HR-10 cam with '062 L31 Vortec heads. It will be a .030" overbore and my target quench distance is .042". I'm having the heads milled .020", screw in studs installed, guides cut down for .500" lift and LS-6 beehive springs installed with Comp Cams retainers which will get me another .050" or so lift clearance. Intake will be a Performer with an M4ME QuadraJet and Doug Thorley 1-1/2" Tri-Y headers. It was a toss up between the L30 and L31 heads as I had both but I already had the new flat tops from an old project and the L30's put my SCR at about 9.9 to 1. I want to be able to run 87 or 89 Octane, the milled L31's will put me at about 9.4. Doesn't seem to be a big difference but it may be just enough. If it were not for already having the pistons I would have used the L30 heads with KB D-cup pistons as the L30 make a little more low and mid range TQ and the chambers wouldn't extend past the bore like the L31 chanbers will. It works but it bugs me.

This build is for my '88 C1500 to replace a very tired LO3, the truck already has a built 700R4 and 3.73 posi and I'll be switching to a 2600 stall converter. I could have just as easily built a roller 350, I have all the parts but I've been wanting to do a street roller cam 305 with Vortec heads for a long time just to see what I could get out of it. The truck was my perfect opportunity. I don't tow with it, only do light hauling, it's not my DD and I'm limited on rear tire size as it has a 4/6 static drop so so there was no need for anything bigger.

 

Im looking into the same kind of build for my L69 305 next year, please, please, please.. tell me how it turns out. My main concern is addressing the issue of heat buildup due to increase in HP and Torque. (The engine already runs hot and has potential fuel boiling issues) Any and all info you can provide will be of great use. Good luck and enjoy!

Chuck

 

My signature has a link to my 305 build. Might be a thing or 2 in there that would be a good read for ya.

 

If you are referring to my post I'm afraid I have bad news. Shortly after I posted the machine shop called and told me my 305 block was cracked through the lifter valley. Cheap roller cam 305's are hard to find around here since most people send them straight to the scrap pile or ask 350 prices for them so I had to dig my 350 roller cam block core out from the dark recesses of the garage and go with a 355 shortblock instead.

After talking with a friend who works for a local fuel distributor I decided to go the other way on compression. He told me to expect to see 85 Octane replacing 87 in our area as "Regular" and anything higher than 89 start becoming harder to find in rural areas and believe me I'm in a RURAL area. This is for my parts chaser and I may find myself needing fuel in the middle of "who knows where" so I decided to give up a few ponies in favor of being able to run on cat pee if need be, it should still have enough HP and TQ to make it a fun ride. I compared it with a 383 I built back in '83 in DD2000 and "on paper" it outperforms that 383 by a considerable margin in every aspect due to the cam and Vortec heads. That old 383 impressed a lot of people 30 years ago but with all the advances in engine technology since then it wouldn't even get a second look today. What I'm building now would have been hot stuff back then but today it's just another "RV" engine. I can live with that. I'm running KB-118 +.030" 22cc D-cup pistons, my block did not require decking so they will be .024" down the hole. My Vortec heads were NIB but the machinist said they usually need a little skimmed off to make them truly flat but not enough to make any appreciable difference in my SCR. I'll be using FelPro .015" rubber coated steel shim head gaskets making my quench distance .039" and final SCR about 8.73 to 1. I was hoping to get a call by now that everything was done so I could start assembling this weekend but nothing yet.

The 305 currently in the truck is not the original and I can't find the engine code for it anywhere on any lists so I'm hoping it might be a roller block but it probably isn't, for now it's still running good enough to haul it's replacement back and forth to the machne shop. Either way I'll save it for a rainy day, I'd still like to build a "hot" 305 someday to drop in something light with some steep gears just for the Hell of it. I still have the pistons and L30 heads.....

 

2nd the last engine I had in my bird was a l30 with a hot cam. stock components except for the cam. for that much cam in a small package it idled well and had plenty of power. my friend gave me a set of old craigers with some 50 series goodyears mounted. I had no problem catching them on fire. fuel economy under normal conditions was not the best. that engine died due to all things no baffles in the valve cover and the junk rubber wannabe baffled grommets that do not work. if I had another engine like this and I needed to I would build it again.


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Hold on, back up. I have a couple of questions.....

1. Budget? Any time I hear about swapping heads on a 305 I always wonder if that's money better spent than building a 350. Plus, there are precious few performance-oriented 305 heads on the market. Stock, stock replacement, L31 Vortec (the 350 version, not the crappy 305 variants) and TrickFlow 305 heads are what's out there right now for the 305.

2. Emissions-compliant build (not necessarily emissions-legal, but good enough to pass a visual underhood inspection)? Original computer controlled Qjet, EGR, cat converter, etc.??