Cobra Jet vs Blue Thunder

fordracer · #1 (**permalink**) 04-13-2002, 07:26 AM

I am looking to make an absolute screamer of a motor here. To be honest the 535hp ford crate motor is looking good. I was just wondering if anybody here uses the Blue Thunder heads and is there any discernable difference between them and the Cobra Jet heads ?

Back in Black · #2 (**permalink**) 04-13-2002, 08:59 AM

Why not just get the 514 crate motor? 600 HP, 590 ft lbs torque, and you will then be happy with the Cobra Jet heads

Second option, is the Merlin Monster motor... 632 CI, 780 HP, 765 ft lbs torque, runs on pump premium

www.theengineshop.com

427sharpe · #3 (**permalink**) 04-13-2002, 10:27 AM

I have used both, and I think the Blue Thunder have the edge, albeit slight. They seem to perform better at lo to mid rpm, and match the CJ heads at upper rpm. I would suggest them if you are going to build a race motor. If you are going to build a street or dual use motor, I strongly suggest using Police Interceptor heads. Even tho they are iron and heavy, they perform better on street duty because they have oe screw in studs and smaller ports with the CJ valves (2.25 intakes and 1.75 exhaust). They perform much better at lo to mid rpm and with judicious porting can match the CJ's all the way to 6000 rpm or so. If you are going to build a screamer motor, than use the Blue Thunder heads, and spend a LOT of time and money in the short block! I mean a stud girdle in particular if you use the 2 bolt block and expect to see some rpm on a regular basis. You can buy the girdles for about 100 bucks. I use the PI heads on my 535 with an SCJ 4 bolt block, and run hi 10's lo 11's in street trim on pump gas. My best run on slicks has been 9.97, but it cost me a twisted axle. I usually limit rpm to about 6800, unless really pushed, when I will go the the absolute max of 7200. To be clear, I usually only have to turn about 6000 or so to abuse the competition! On a less aggressive slick I have run lo 10's. And my motor isn't all that wild! Roller cam, roller rockers with the typical machining duties. I enjoy the daily driver aspect, while still being able to shut down competitors and the local tracks, and drive home while they trailer! If you get a set of early 429 heads, they have the screw in studs and can be machined to CJ valve size, thus making your own PI head! Just clean up the exhaust ports, and go racing!

cobrashoch · #4 (**permalink**) 04-15-2002, 11:10 PM

I'm with 427Sharp. My first cobra motor was a cop car headed motor that was by any standard enough. My latest entry has Blue Thunder heads,main stud girdle,(more later)intake and damper. Dyno numbers on the B.T. engine was scary. I had the engine detuned a bit later by raising the compression ratio to about 9.0 and reducing the boost to about 7lbs. This gave me the torque numbers I was looking for on the bottom end. Thats where the B.T. stuff worked the best, at least with my limited dyno time.
As fot the B.T. main girdle for 2-bolt mains, it doesn't cost 100$.
But it's the best there is out there for a 2-bolt block. PERIOD!!!!
I am of recient hearing good stuff about the Edelbroch(sp?)heads they are selling for 385's. Seems they work about as well or maybe better than the old police heads when pocket ported, as is popular right now.
427SHARP- Your times are where I want to be soon. I specified to my engine builder a 9.90 index car motor at 2800 lbs.(mininum) My builder told me this engine is a beast and looking over your times I think I made some good choices. I have had to switch to a Coan tranny though and am saving my pennys for a Gear-venders overdrive. Maybe this summer........Have you got your car NHRA certified? I'm having fits with those guys.
cobrashoch

JGunn · #5 (**permalink**) 05-07-2002, 04:37 PM

Back in Black: The idea of money has to enter into the question though. The engines start to get a little pricey.

Quote:

Originally posted by Back in Black
Why not just get the 514 crate motor? 600 HP, 590 ft lbs torque ... Second option, is the Merlin Monster motor... 632 CI, 780 HP, 765 ft lbs torque, runs on pump premium

Great Asp · #6 (**permalink**) 05-07-2002, 05:17 PM

Hey, I went to that there Merlin site, but all dem motors have the distributor at the wrong end of the engine!

BIB is right about his 514, it is a screamer! Rode in one, scared me, and Im fearless !

Great Asp

trudellt · #7 (**permalink**) 05-07-2002, 05:55 PM

fordracer,

I don't know specifically the difference between the CJ and BT heads, but the intake on the 514 requires some thought (if you decide to go that way).

Competition out of Ohio built/installed my 514 (starting with the Ford Crate - and CJ heads). The single plane intake was sold and they fitted mine with a Holman Moody dual plane (which is rare), but they really liked it.

Just something else to keep in mind if you plan on any street use.

Oh, one last thing. I have Goodyear 295's on 15" wheels, and the previous owner warned me about breaking traction under full throttle on I-75 - at 85 m.p.h.!!!

Think about that before you overbuild. The 514 is a beast. You need slicks to really feel what it has to offer as it is.

I don't want to get your thread off-course, so I'll shut up.