Food for Thought
 

Having time to daydream, I wonder if any of the smart people (unlike this writer) who kept their original 427/428 Cobras into the chassis dyno era had them tested with the as delivered, under the car exhaust system. When installed in the big Fords, the 427 was equipped with heavy, but efficient looking cast iron exhaust manifolds. These were a no go in the Cobra engine compartment, so clunky 390 units took their place. On the high revving 427, this change had to have killed power over 5000 rpm. Recently, a friend with an ERA sporting a built 427/454 engine with a strong cam and side pipes ran his car on a Dynojet and could not hit 400 at the wheels, which led to my original question.

probably restrictive sidepipes

I hope to hit 300 at the wheels with my built 470 (455HP/500 ft-lbs flywheel dyno) due to the lack of hood scoop and restrictive under car exhaust. I figure it will be plenty for a 2300 lb car.

Funny I never dynoed mine but, I can tell you 3rd gear, just step on throttle, no dumping of clutch and,the tires will go up in smoke. 315 17 nittos 600 hp I am told and I believe them!

Hauss,

Apologies in advance; were you using one of these: Butt Dyno - $529.95 : KaleCoAuto.com, Your home for the rare, unusual, and hard to find auto parts.

Sorry - couldn't resist...

Tom

Chassis dynos are notoriously inaccurate, the dynojets always read too high, the tuners will tell you the Mustang dyno is more realistic. Dyno jet is akin to running the car down hill while the Mustang puts more load on the car. Albeit the engine dyno still the gold standard.

I was never given a chart I was only told by past owner. Car has a stroked man o war block huge cam 0 vac at idle and a 780 cfm quickfuel carb victor aluminum heads.3rd gear will boil the tires no kidding! I would say 600 hp but I never personally dynoed the car just comparing to other cars I have worked on.

I had mine on a dyno and it read 452 rwhp. If you factor in a 17% parasitic loss, that is about 544 crank hp which was just shy of where it was supposed to be.

The problem they had with my car was the tires. They were older tires and due to the light weight of the car and IRS, were slipping on the dyno. I think the dyno was a Mustang with 24" rollers. I have not put it back on since the good tires were installed.

The last time on the dyno, with MT ET/Streets, hit 682 TQ @ 2700 rpm and spun the tires.

I've posted this before. Mark Donohue once said " If it wouldn't spin the tires in top gear at top speed then it needs more Horsepower" Nuff said :) Cheers Tom.

Keith Craft once told me that of the engines he dyno-ed and then installed into a Cobra, and then chassis dyno-ed he saw a 20% loss.

Personally If it runs crisp, no pinging no blubbering, then I would be happy. You could have 1000hp and, if it ran like crap, you would not be happy.That is what you should be looking for, not hp numbers .Now that"s food for thought.

BUTT dyno
 

35$ levi 505 comfort fit butt dyno:D

Lol!!

Glad to see you get what I am saying you are one of the few.:cool:

I think on his restoration motors like 428 CJs he probably ran the stock manifolds on the dyno. But on custom built engines KC used tuned headers on his dyno runs - at least going by my experience. So taking a 500 HP engine and installing it in a chassis with 390 log manifolds would probably kill the upper end and could possibly cost 25% at the rear wheels in theory dropping such a motor to below 400 HP.

The day they dyno tested my engine they had three 428 CJ restoration (stock) engines lined up outside the dyno room they had just finished breaking in and running. I asked the dyno operator what they typically made and he said usually stock they pulled about 410 HP. A 428 CJ is not very different from a Q-code 427/400 HP center oiler from the 63 - 64 era other than a bit less bore and bit more stroke and everyone knows by then the 428 CJ was grossly under-rated by Ford at 335 HP. So the 410 HP would seem to compare pretty closely to what Ford rated the 427/400 engine at - but both 427 Q and 428 CJ ran a more efficient exhaust manifold than the 390 log manifolds.

Detroit wasn't messing around with HP ratings too much until the later 60s and their engines in the restoration dyno reports I see in magazines like Car Craft and Muscle Car Review seem to run right on the old manufacturer ratings for the most part. Course that was stripped of accessories and the old rating system.

Closer to the answer i was seeking. The resurgence of the 427 vs. 428 debate really inspired my original post. Given the differences between the two, I suspect that those 390 manifolds hurt the shorter stroke/higher revving 427 more.

I guess I should have said also a bit less cam and compression. And I think KC's assembly care was probably a bit greater than standard FOMOCO at the time.

I would say so too. Using Chevy for a comparison may not be popular but the 427/390 L36 hydraulic motor was rated at 390 HP in the Corvette with streamlined manifolds but lost only 5 Hp when put in an Impala with log type 396 manifolds and Chevy very clearly said it was due to the exhaust. The higher revving 1965 396/425 Corvette with streamlined exhaust manifolds dropped to 396/375 when it was put in the Chevelle that year with a bit milder hydraulic cam (vs mech in Corvette) and standard 396 manifolds to fit the chassis. Even later year 396/375 motors with the L72 mechanical cam kept the 375 rating with the log manifolds in the 66 and later Chevelles, Camaros and Novas.

What would have been interesting was if someone back in the day had run quarter mile times between a 428 Street Car and a 427 Street Car to see what the difference was. Since the 390 manifolds probably hurt the upper end of the 427 more than the 428 there likely wasn't much difference between the two in a 2500 lb car with 7 inch wheels and standard tires back in use then.