Blue Thunder Vs Cj Alumn Heads

cobra fever · #1 (**permalink**) 05-20-2003, 12:56 AM

i got the alumn. cobra jet heads. Am looking for some more hp, would I get more out of blue thunder stage II heads? or can I match my existing ones if I was to port it out? My engine is a 520
stroker with double holley 600's, blue thunder intake, cj alumn heads. Dynoed 435 rwhp. Want to change the cam too. If someone can help me with desk top dyno too see what combo will get me the most hp
THANKS GUYS

Naja · #2 (**permalink**) 06-22-2003, 11:50 AM

The guy who built my engine runs stroked 460s in the cars that he and his sons drag race. He only uses Blue thunder heads because they flow significantly more that other heads.
I put the new Edelbrock heads on mine because they flow better than CJ but not as much as Blue Thunder - better from street use.

Regards,
Frank

cobrashoch · #3 (**permalink**) 06-27-2003, 04:04 PM

The Blue Thunders are a mid to high end range head. The CJ heads are a high RPM head (all 3 versions) and will make more high end power. In a 2500 pound car like a cobra I doubt you will see any differance between the two. I wouldn't recomend porting the B.T. Chevy port head on a 520 though. Just pocket port "em" and clean them up by smoothing out the ports and keep the compression down to about 9 to 1. That combo will get you to around 600 honest horsepower and on pump gas to boot. Any more power than that will require some big time "beefing up" and will make your car heavier and be very costly. I'm using the stock port Chevy B.T.'s on a 545 and a supercharger and the bottom end charge is unbelievable in ANY gear. In short, if you go bigger in cubes don't go wilder with your parts. Sage advice you won't regret. I also recomend you use the Chevy rod setup if you can afford the the extra cost of the crank too.
cobrashock

SFfiredog · #4 (**permalink**) 06-27-2003, 10:30 PM

One thing to consider with the Blue Thunder heads is that the exhaust port location is raised 5/8" on the standard 429 CJ port.
Headers designed for a 429/460 will bolt on but the raised port may cause fitting issues in your car. For example, a 5/8" raised port in a Superformance with a 460 will cause interference with the steering shaft and may cause the side pipes to hit the top of the cut out in the body.
HTH,
--Mike

cobrashoch · #5 (**permalink**) 06-29-2003, 12:42 AM

Mike- good point. Headers for Blue Thunder heads are non- existant on Cobras, esp. the Chevy port jobs. Custom manufacturing required. Been so long that I forgot that little fact.
cobrashock

BagHorn · #6 (**permalink**) 07-07-2003, 01:30 PM

I actually have the Blue Thunder Stage 2 heads with the Ford exhaust ports (versus the Chevy) on my stroked 460 (545 cubes). The Superformance headers and pipes work fine as long as you don't get the heads with the Chevy exhaust ports.

I'm running a Blue Thunder dual plane/dual carb intake on top of that and everything fits nicely under the hood. I got the carbs with the manifold and heads directly from Blue Thunder...they offer custom built 650cfm Holley specifcally for that manifold. I'm also running 10.5:1 compression ratio. I add a can of octane booster to every tank of gas for insurance and had it tuned that way as well. It runs great.

I set my car up to be very driveable on the street and not just a max horsepower, high rpm screamer. It starts on the first crank even when I haven't driven it in weeks and has a nice lumpy idle but it doesn't make the car hop at the stop light as I've seen some do. They ground the cam based on my desire for street-ability over maximum peak horsepower and I really like how it turned out. It's hydraulic roller with a 238 intake and 246 exhaust duration @ 0.50 and .638 intake and .661 exhaust lift with 1.8 roller rockers.

It's fine in traffic and will snap your neck at any time if you get on the gas especially when you feel all those barrels opening. After 500 miles I had it retuned on a chasis dyno and it put out 514 hp at 5400 rpm and 554 ft. lb. of torque at 4200 rpm at the rear wheels even with the Superformance IRS. My mechanic said he could get another 20-40hp out of it if he spent all day on the dyno really fine tuning all the settnigs but it runs great now and I figure I have to save something for later.

I generally shift in the mid-5000 rpm range under hard acceleration and have the rev limiter set to 6000 rpm...I'm running a TKO II transmission and a 3.27 rear end with Auburn Pro Locker.

All in all the car has turned out just the way I'd hoped it would when we were selecting the parts. I'm very pleased with the outcome...it's a very enjoyable combination of a car with reasonable street manners and an e-ticket ride, neck snapping acceleration and brute power. It's the first car/vehicle I've ever had or driven where I'm not sure if I really want any more horsepower than what it's got...I'm not scared of the car but I do have tremendous respect for the insane power to weight ratio the car has at it's disposal.

cobrashoch · #7 (**permalink**) 07-12-2003, 09:57 AM

Baghorn- a 650cfm carb on a 545? HMMMMMM!!!!I'm using the same manifold but with a dominator flange and a 1050 "in the box". It's still not quite enough.
Whos lifters are you using? Been thinking about switching over for a while now. Of presant, I am using Crane solids and aluminum rockers but thinking in terms of hyd. lifters and steel Comp. rockers.
I am using a Auburn pro locker too, and am very happy with it. But around these parts it has fallen from grace, and for the life of me I don't know why.
cobrashock

BagHorn · #8 (**permalink**) 07-12-2003, 11:09 AM

Hi Cobrashoch, I should have been more clear...that's TWO 650 cfm Holley's on the Blue Thunder dual plane/dual carb manifold. They also provide a nice progressive linkage and I can feel the point in the throttle where it opens up all the barrels...prior to that point in the throttle travel it drives along very well behaved...after you mash through that point all hell breaks loose.

Have a good one