Hank

I'm running a 502 in my 1966 convertible and would like to upgrade its performance as a winter project.

My baseline is 335 rwhp at 4500 and 445 ft lbs at 2800, on a chassis dyno. The car is very responsive and torquey and revs happily to above 6,000 (but obviously pulls harder below that). The engine has a stock 502 short block, iron rectanglular port heads (3919840 -- closed (109cc) chambers, sources I have say they have 2.06/1.72 valves), GMPP hydraulic roller cam, roller rockers, single plane weiand intake, 750 dp Holley carb, factory exhaust manifolds running through side exhaust.

I would like maximum tire melting HP and torque, consistent with pump gas and midrange responsiveness. I drive the car a lot in the summer.

My upgrade plan is to switch to
1. GMPP aluminum heads (1236400), 119cc chambers, 2.25/1.88 valves
2. Crane 168741 hyd roller cam (.610/.632" lift, 236/244 duration at .050)
3. Hedman headers (1 3/4 primaries) feeding JCL baffles under sidepipe covers
4. Demon 850dp carb.

I already own the headers and carb. I would of course prefer 2" primaries on the headers but I am inclined to run what I have.

I am about to order some parts and would appreciate any suggestions or experience others have to offer. Especially regarding the GMPP heads vs. say the Edelbrock Victor Jr. CNC ported heads, which are about $1k more per set.

I am a little worried that the lower static compression, higher overlap cam, bigger carb, and bigger ports will make the combination a little soggy. What do you think?

Thanks for your input
Gerry

PS -- 3.36 rear gears, wide ratio muncie, runs 12.70/111 now.

wallyknoch

Dart heads would be a good choice as they have several styles. Instead of a hydraulic cam, I would recommend a solid lifter style as the heads work better at higher RPM`s I have a similar set up in one of my pieces and it runs low 11`s at 120 + driving it on the street. Add some compression and at least a 4.10 rear and hang on! :D

69 N.O.X. RATT

Due to the fact you have 3.36 gears, and I prefer Oval port heads in motors less than 540 inches, or 650 HP that is the first thing I would do. Do not believe Ovals can not support your motor. I made 450 HP (5900 rpms) and 470 TQ (4100) at the wheels with stock Oval Edelbrock and a solid roller (454 in motor). With your set up (3.36 gears) that motor wants a good TQ set up, it will be faster in street condictions with Ovals. Depending on how much money you want to spend is the issue. Edelbrock makes a CNC version (112 cc's) of their oval head that flows around 320 at .650 The GM ovals are 110 cc and flow very well for a stock head 310 or so at .650.

For Maximim streetable HP the cam you are looking at is maybe a little small, but then again it would be very torquey. The cam from the motor above was 242 and 248 at .050 and .646 / .653 lift. It made max power at only 5900 rpms in a 454, so in a 502 it would probably be even lower. Where the motor makes max power, rpm, wise is very dependant on the duration of the cam. You can't go to big, cause it will kill the bottom end (not good with 3.36 gears), but 245 + at .050 on intake and 250 + exhaust should be pretty safe, and make very good power.

You can mill the heads to get a little more compression. I do not know if the above heads will fit your poistons. :chevy

69ttop502

Hank, I am going through this right now as well with my crate 502. Mine is the 8.75 to 1 compression version, not sure what yours is but if you have the same JE pistons as me you are probably at 9 to 1 or so with the 109cc heads. I agree with the others above but would say don't be afraid of the rectangle port heads even though you don't need them for what you are trying to do, but I am guessing you already have your intake as well. I ended up ordering a pair of Brodix BB+2's angle machined to 100cc chambers to get me up to about 10.5 to 1 with my stock pistons. The main problem here is going to be exhaust as the exhaust ports are raised. I am going to run a solid flat tappet with .615 lift and 258 duration at .050. In talking to others and from my own experience with my motor you really can't kill the bottom end on a 502 at least in lighter cars and especially 4 speeds unless you really mismatch things. I really recommend a solid cam whether flat tappet or roller. You can get away with a little less compression with the roller all other things being equal. Hopefully some more of the experts like 427HotRod and Mountaainmotor will chime in here. Good luck, Bill.

clem zahrobsky

with headers and low restriction after market side exhaust you will see 50/100hp gain over stock exhaust manifolds and stock chevy side pipes. the stock type side pipes are big HP killers on BBC. :chevy

69ttop502

Hank, what Clem said is true about the exhaust. If you run the JCL baffles you will have the best flowing system you can get for a big block. I dyno tested these baffles and the results were remarkable. Bill.

Hank

Thanks everyone for the thoughtful replies. Clem and Bill, I am definitely going with JCLs to uncork the exhaust.

Bill, 100cc chambers with BB+2 ports should be a great combination. After you mill the head, what other changes are then needed? (eg, mill the intake, put spacer under distributor, custom length pushrods?). About how much does the machine work cost?

I have been playing a lot with different combinations and if desktop dyno is to be believed, a killer combination would be to just upgrade the -840 iron heads to bigger 2.19/1.88 valves and add the 168741 cam and the headers. That would give me (believe it or not) 574hp, up from a baseline of 388. The program is telling me that the extra flow of aftermarket aluminum heads is largely offset by the loss of compression ratio from the 118cc chambers. Bill I guess you already figured this out!

Anyone have closed chamber, rectangular port, thoroughly ported BB heads for sale?

69ttop502

Hank, having the Brodix angle machined cost 250 and they also mill the intake side so the manifold will be fine I hope. right now my engine is out to be freshened even though it only has 7500 miles on it I want to do this once and not again for a long time. That is my dilemma, the pistons look like new so I don't want to change them but they only have a 1cc dome so to have any compression at all I needed the 100cc chambered head. The other problem I have found is that my pistons are .017 in the hole so my 8.75 crate motor was really 8 to 1 or even less. It originally had the open chambered version of your head on it with the 325cc rect. ports and even with that head and the low compression with a mild hydraulic flat tappet the car had alot of bottom end. I have gone round and round on the head thing and the consensus was that the raised exhaust port could be worth as much as 50 horsepower so for that I will make the headers work somehow. As of now I haven't done or even priced any of the machine work yet but I will soon and will let you know. I think you sound like you are on a good track. What is the cam that you posted, is that a solid flat tappet? Bill.

69ttop502

Hank, sorry just saw from the previous post that the cam is the Crane Hydraulic roller. Scoggin Dickey use a cam almost identical to that in their 602 horse 502 so I definitely believe your Desktop dyno numbers. Should be a killer. How much does a 66 Ragtop weigh?

Hank

I haven't used the crane 168741 cam yet but desktop dyno loves it and I also noticed that Salee Chevrolet offers a 630hp 502 that uses this cam. And I saw a shark for sale on ebay with this cam, emailed the owner, and he replied that he loved the cam (ides at 850, runs like stink).

I think my car weighs about 3400lbs. Not sure. Glass spring, no spare.

On the header problem, I've been researching too. I bought a set of new Hedmans made for BB side exhaust but now I'm thinking that their 1 3/4 primaries are really toooo small. And it's the OD that's 1 3/4 on these things. It sounds like a detail, but when I measure the ID of the primary at the gasket face it's smaller than the exhaust port by 1/4" at the edges and 1/3" at the corners (square port, round tube). Also though 1.75 vs 2" may sound trivial, a 1 3/4 primary has 24% less cross section than a 2" primary, and GM and others who dyno these engines (in 500-600hp trim) use 2" primaries.

A long winded way to say I'm looking at header options. Most interesting at this point is Stainless Works, who offers a BB vette stainless steel header for $800. Not sure how hard it would be to adapt to side exhaust, they claim it's possible, I will call them tomorrow. Since they're stainless you avoid a ceramic coating cost layer, which makes $800 look almost reasonable. Stahl 215s look pretty cool but at $905 painted that's kind of steep, and Sanderson BB1s are super-short block huggers that honestly don't look so much better than manifolds in terms of flow.

I love planning this stuff! Can't wait to get it all together and fired up.

Hank

One other thing -- compression. I have the stock 502 JE pistons (nearly flat tops) and with the closed chamber heads, they should have developed about 9.5:1 static CR. When I ran a compression test this summer, the numbers were a consistent 200 PSI. Seems pretty high for a 9.5 engine? I know the cam and cranking speed have some impact also.

c5thriler

Hank,Thought you may be interested in my combo.When I bought my ZZ502 back in 2000 to start my restomod project I changed the cam to a Crane 598/610 lift hydraulic roller with duration 230/236 @ 50 with lobe separation of 110.Crane told me that that cam would give me 40 hp more than the std cam.I still use the 1.70 ratio rockers.(This is not a drag car as with 8"wide knock off wheels it will never truely "hook up").

I had the stock alum heads pocket ported and am using the stock Holley 850 carb (dual feed single pumper)with 74/78 jets.( plug color looks perfect).After installing a Tremec TKO600 5 speed with a 2:84 first gear & a 3:70 rear gear I basically had no first gear as I would be at redline in what seemed 20 feet so I changed the rear gear to 3:36 which gives me a usable 1st gear and more time to shift from 1st to 2nd w/o bouncing off the rev limiter.

I have stainless steel custom headers by the Stainless Works here in town.It has 2" primaries into a 3" collector which in turn dumps into 3 1/2" side pipes using Spiral Turbo Flow mufflers.Timing is set at 39 degrees total.(initial timing is 21 degrees with the balance of 18 degrees in the MSD distributor.

On the dyno last week this combo made 361rwhp & 419 tq.With no air cleaner in place it made 367rwhp & 434 tq.I am using a std L88 drop down air cleaner base with a std 427 air filter element & it barely clears the std 427 hood bulge w/o hitting.The dyno guy said the air cleaner was very restrictive and did not let a lot of air into the carb and he recommended a K&N filter element which permits air flow from the top of the air cleaner as well as around the sides.He said with that in place I should be easily be able to closely approach the dyno figures with the air cleaner assembly and filter off.(The engine currently has about 18K miles on it)

I would like to know if there is a formula to figure what the gross hp & tq would be on a non rear wheel dyno?? Can anyone help with that question? Brock

396375

Hello Brock.
That's about 422 HP at the flywheel.

uxojerry

Hank - You have many options and they will all cost $$$, lol. I would contact Eric Weingartner, Chris Straub or Mark Jones for some recommendations.

Another option is to go over to the Chevelle Forum, Performance Section and see what other guys are doing with the same issues.

I would plan for a new top end swap and consider swapping pistons. That engine is capable of 700hp with the right parts. AFR 290/300 oval ports, or AFR 305/335 rectangle ports would probably be worth further research. A piston swap is expensive but makes for a better performing combination, IMO.