I'm looking for some alum heads to substitute for the stock cast iron one's on my '69 L71. I want to continue to use my tri-power intake and stock exhaust manifolds. In order to use my tri-power remote heat activated choke mechanism, I need crossover heat. Is there a nice alum., rectangular port, crossover heat head availablel? In looking through Jeg/Summit catalogs, the pictures shown only indicate Edelbrock's have the crossover, but their detail info. page states no heat crossover. Also, the Edelbrock heads may require changing pistons from my stock high compression, closed cylinder head design. I don't want to change the pistons since I probably only have 5000 miles on these. Anyone using the Edelbrock's that might have info.?

PS, will also be going to a hydralic roller cam at the same time, but I hope that is all the money spenders.

Any help would be appreciated.

Ralph.

 

I'm almost certain the eddy heads will work with your pistons, being their closed chamber designs. Just order them from summit in case you need to send them back. They'll take 'em, no questions asked.

 

I have the Edelbrock catalog and have been reviewing it carefully. The E-street and Performer are both oval ports, not the rectangular I need.

Note in catalog quoted as: "Notes for all Performer and Peformer RPM big block chevy heads: Spark plug is closer to center of bore, will interfere with high dome pistons for open chamber heads. Use pistons designed for our heads. Match with Edelbrock head gasket sets on pages ..."

I have closed chamber heads, but do not know what the differences are. I will check with Edelbrock for comments before ordering, but hoped someone here had specific knowledge.

Thanks, Ralph

 

I wasn't sure what your chamber size was so I poked around a bit. Here's an article about a 427 build that may have some helpful info. http://www.corvettefever.com/techart...d/viewall.html

The most important tidbit IMO is the part about valve clearance on the intake side and how they relieved the pistons to obtain sufficient clearance. You can find this info just below the multiple pics of the heads and valvetrain. When I changed the cam/heads on my L36 (the bottom end was fresh and I'm pretty sure I have the 2300 pistons too but they had been milled to give me 9.5 to 1 comp. ratio w/ factory heads) I went through that process too because we encountered the same issue. We needed more clearance so we used a special tool to relieve the pistons while they were still in the bore but we also needed to do light cleanup work by hand around the edges of the valve pocket. Depending on your cam selection you may or may not have that issue but you will definitely want to check and be prepared for it after your cam is installed. The old clay in the chamber/with the head bolted on/while rotating the engine technique is what we used. If you need more specifics on this just let me know. My cam specs are in my sig.

 

Les, great info., I'll review article. My current heads are the stock closed chamber 106.9cc models, pistons SpeedPro TRW L2268F30, which gives me about 11.25 CR at sea level. I figure at Denver altitude, I'm running closer to an effective 9.6, which is fine with our premium gas.

My proposed cam specs would be near are slightly lower than yours.

Thanks, Ralph

 

http://www.airflowresearch.com/index.php?cPath=68_71
Check with AFR on piston clearance. The flow numbers on these are as good as many much bigger port heads. They match up well with your factory intake ports and build specs. If your going Hydraulic roller a decrease in compression will be a good thing and allow a better cam operating range. They come in a 114cc version.

 

AFR's will have a raised exhaust port which will require some exhaust fabrication and possible bracket problems. For what you're doing, you need a standard location exhaust port. Brodix Race Rites or the Edelbrocks will fit the bill.

Also, I don't know of any BB aftermarket performance heads that use the 'exhaust heat crossover'. You'll have to adjust the choke mechanism to open the choke with a cooler intake. No big deal, plus, a heated intake charge hurts HP.

Is there anyway I can talk you into some headers, big pipes, and Super Turbo mufflers? I think an exaust system would be worth 50+ HP here.

 

The oval port Edellbrock's say they have heat crossovers, but not sure of all their BB heads. The pictures show opening in the crossover spots, but not sure if internal castings allow for heat. I'm not building an all out horsepower engine, so crossover heat and headers are not an issue with me. I have chambered exhaust, but stock BB exhaust manifolds. I've been the header route before and don't want the hassle. I like Brodix specs., but lack crossover?

Does GM still make an alum. BB head?

Thank, Ralph.

 

GM's aluminum BBC heads are made by Edelbrock, with all of the same good & bad points.

 

Back when I looked into Edelbrock BBC heads (some years ago, maybe something has changed) the only difference between performer and performer RPM heads was that the performer had a drilled passage from the exhaust x-over port to an exhaust port. The rest was the same. The performer heads even had the performer rpm part number cast into them. Those were roval-ports.

Maybe the same deal for the rectangular ports? If so, any machine shop should be able to drill the hole for you.

 

Ralph,

Remember that compression ratio does not change at altitude. However, what does change is overall cylinder pressure as at altitude less atmosphere is drawn into the cylinders with a naturally aspirated engine. Were your engine turbocharged, the cylinder pressure would be the same at sea level as it would be at 5,000 feet ... as the wastegate controls overall intake pressure.

Wording nuances aside ... yes, your engine will operate more like a 9.5:1 engine at 5,000+ feet altitude than an 11.5:1 engine.

 

The ports are raised .300. The head sits @ a 45 degree angle. Port is about 1/8" higher and 1/8" outboard of stock. I would think with dual exhaust there will be no issue with clearance or fitment anywhere.
Here is the big difference.
GM 990 iron head Flow @ .600 lift 292 intake, 204 exhaust
Edlebrock 454 R Flow @ 600 lift 314 intake, 228 exhaust
Brodix Race Rite Flow @ .600 lift 334 intake 217 exhaust
AFR 305 rect port Flow @ .600 lift 363 intake, 276 exhaust
With factory manifolds the difference in flow especially on the exhaust side I could see an easy 30 HP difference in power across a good portion of the operating range of the cam with the AFR vs the best of the others.

 

Actually they're 0.375" so it's about 1/4" up and out. But with factory manifolds, that won't matter.

Big ditto on everything else. The Afr will work with those pistons too.

 

All great, but can I use a factory choke?

Ralph.

 

See if AFR will machine the crossover into the head for you. They have the CNC equipment and head blueprints.

 

The Eglebrock RPM 454R does have the crossover.

 

Mako, I wondered about that. In looking at their pictures in the catalog, all their BB heads (except the racing models) have the crossover passages cast into the intake manifold mating surface. Not sure if this is just a carryover from the original GM castings, or what. The question that occurs to me is, do the casting passages continue into an exhaust heat source, or just false surface passages. It was stated above that a hole is drilled in some of the emission models to provide for choke heat. The text in only one of their catalog models (Performer & Peformer RPM 454-oval port) specifically states "Performer applications include heat crossover passages for emission related engines".

I tried to call Edelbrock, but spent too long listening to music, and finally hung up. Will try later.

Thanks, Ralph.

 

Update from Edelbrock. Their rectangular port BB heads do not contain a drilled heat crossover. They did send me their tech. drawing of where to drill hole to accomplish same. None of the other head suppliers could offer any suggestions, other than random drilling in the head (and that's what I really wanted to do, and try to not strike water).

My current question to Edelbrock is what pistons fit their heads. No answer yet. Their catalog has the helpful comment to "Use pistons designed for their heads". I understand you should check clearances upon any buildup with the clay method, or otherwise. But, surely you don't buy pistons *****-nilly, install them, and then find out domes/valves cannot be made to fit under any circumstances. Am I being unreasonable, or is there information out there?

Thanks, Ralph.

PS: my current pistons and specs are outlined above.

 

PM sent

 

I have a 70 LS5 454 and have a heat riser eliminator from Paragon (part#660). I have used this with both a Corvette Aluminum intake #3919849 (spreadbore) and 3937795 (oval port TriPower). The choke works fine IMOP. I use crossover blocked off intake gaskets. Having built so many engines over the years, the burnt/crystalized oil under the heat shield is what prompted me to do this. It builds up so thick that it eventually starts breaking off in chunks and falling into the lifter valley and oil pan. I have pictures if you need them. It's just one of those things that bugged me. I suppose it must inherently take a little longer for the mechanical choke spring to react... but... the choke seems to work fine with the passage blocked. Just another perspective to consider. Not a cult.