I've decided to "kick it up a notch" and plan to have some performance upgrades done to my 69 350/300 before the spring season. Thought I would start with new heads and if I'm doing the heads, a new cam. At this point, I'm thinking I'll change the carburetor and possibly the intake manifold. I'm thinking fulie heads and a very streetable cam. Carb to match (600 - 650 CFM). Recomendations/advice please?? As always, thanks for making the time to answer.

 

And your budget is?

 

Mine or my wife's? LOL!!
Actully budget around $2,500 each spring for various projects.

 

As said many times, no carb swap will be an 'upgrade' and going down 100CFM to a 650 is going backwards.

 

What do you mean by new heads, aluminum or cast iron double hump? Your 300hp engine has "small" valves, you'll want to get heads with 2.02/1.60 valves. A properly set up quadrajet will be more than enough for your car.

If you do the heads, you'll also want to do the cam/lifters, intake manifold and possibly headers. With a stock hood you will be somewhat limited with intake manifold choices. The stock iron intake manifold doesn't flow that well and realistically can only handle up to about 350hp (gross).

What is your final goal? You can get into a situation where you're spending a bunch of money and only gaining 50hp.

 

In 1969, the base engine had 10.25:1 compression. Both base and L46 were equipped with the camel hump '186' casting cylinder heads. If your heads are 'stock', they likely have the smaller 1.94/1.50 valves. L46 had 2.02/1.60.

With this difference and if you want to keep it all stock-appearing, I would find the better but very scarce L46 186 heads with a good refresh and 3-angle valve cut.

if you want to go aftermarket, I'd go with either the DART 180-195cc intake runner heads or a good pair of World or RHS heads with the large valves 2.02/1.60. Most come with 5-angle valve cut, closed chamber and much better intake/exhaust flow capacities.

I would also get a good aftermarket cam kit (cam, lifters and springs). Something with no more than 230 duration at .050 to keep it streetable with .470-.480 lift in a flat tappet cam. If you wanted to go with a retro-roller kit with greater lift yet great street manners (see my signature), you could spend close to your $2,500 budget including refresh of the cylinder heads. Be sure you get good set of pushrod guideplates (if not installed). I am also assuming the heads have screw in rocker studs. If you went with a retro roller kit, you would get a very comprehensive top end refresh kit.

This would really waken up your base engine while keeping all outward appearances unchanged. If you already have a performance exhaust, it will be even more noticeable.

 

Guys - thanks again for your input and advice.
Mike - I don't want to "under carb" the engine - I just want to make sure I don't "over carb it.
Revi - definitely cast iron double hump with the larger valves. I would like to move away from the stock manifold but have no desire to change the hood. Swapping the carburetor out because its "tired" - I suppose it could be completely rebuilt but not sure if that's the way to go (plus, while the engine is original, the existing carb is not). With respect to your question about my final goal, I would say an increase of roughly 75 hp is where I would like to be.
TedH - stock - appearing is important to me and definitely will not consider aftermarket (for the heads). I'll most likely look towards Crane for the cam - performance minded but very streetable. I currently have Flowmasters installed and am not considering headers (would love to find an original set of side pipes and will sooner or later).

 

What you've already got is just right.

 

Your carb can be rebuilt and tuned for increased performance. Lars rebuilds and tunes quadrajets and Holley carbs as well as the OEM Delco points-style distributors. He could lay down a major update to both carb and distributor to get the most out of your engine; taking into account your planned cam/lifters. My Crane Energizer cam/lifters was a bit dated but it sure woke up my L48 and has the same lift but shorter duration than the L46/L82 cam. With your higher 10.25 compression from the 64cc chambers, you would see more benefit from a cam with lift in the .470/.480 range. You may get 75hp (gross) from this total update. Your stock cast iron dual plane intake is practically identical to the Edelbrock Performer. You may see some improvement adding a Performer intake. I am not aware of the max lift that stock style springs will support. If you consider anything over .460 lift, be sure you have sufficient valve to piston clearance and do not experience valve spring coil bind. Fresh valve springs are a must with any new cam/lifters.

You could have your 186 casting heads reworked and the larger valves added if so desired. Being heavy, closed chamber heads, they will also tolerate porting and bowl blending by a reputable machinist. That way, they are the original heads; just updated. An option would be to find a freshened pair with the larger valves.

Be sure to share what you decide and post updates as your project progresses. Always good to 'listen in' on others' builds.

 

a elderbrock performer will fit under the hood and make more power .I second the roller cam if the budget allows ,but the newer hydraulic grinds will add power over the original GM grinds.you can find new after market iron heads for $600 at competition product ,or on E-bay.

 

Why not build an L-46? You've already got a start on it and won't need any aftermarket parts.

 

I thought all camel hump heads contained 202 valves, didn't know they varied.

 

Yeah, I had to dig into my small block chevy cylinder head book to get the details. 186 castings came with both small and large valves. 300hp had small, L46 had large from the info I found. L46/LT1 essentially shared the same cylinder head. The base 300hp engine was same engine across several models of Chevrolets (Camaro, Impala, Corvette, Chevelle).

I found this from a forum post from 2009:

http://forums.corvetteforum.com/c3-g...g-numbers.html

"Jan 16, 1969 Casting date 186 heads NCRS CORRECT! if your Vette's build date is later than January. Good heads but don't have hardened exhaust seats for unleaded gasoline, run a TEL additive from Jack Podell or other source. Same heads as 350HP and 370HP high performance 350's without bigger valves, if you seats are bad they can be opened up to 2.02/1.60 valve sizes but, make sure the machinist opens up the combustion chamber wall for larger intake valve or it won't flow and better that the smaller valve sizes. Find a shop with a Sunnen VGS type of cylinder head machine for re-building them whan you get around to it."

 

My build date is 27 June 1970. I believe the previous owner had some mechining work performed on the heads but I don't know to what extent. The car runs great with whatever size valves are installed so I won't be doing anything to the heads for a long time (I Hope).

 

If you go with a new cam/lifters, I recommend matched valve springs and new valve seals at minimum on your cylinder heads. Figure the valve springs are 43 years old and tired. Add new long slot rockers and anti-gal pivot ***** (assuming you go stamped steel rockers). Good insurance.