Author Topic: 428 Cobra Jet - iron heads, iron intake, cast manifolds - 450 HP on dyno  (Read 14368 times)

Barry_R

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Me too...
I just follow customer requests.  This is a really nice numbers match kind of car.

crenbbf

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Hi Barry

Thats a nice set up

If it were me and on your side of the pond, I think I would have asked you to sneak in a 4 1/4" Scat while the motor was apart no one would be any the wiser.

just sayin'

Barry_R

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Did not take it up to 6000 with the headers - but I suspect that you are correct.  The manifolds were not as bad as I thought.  Probably a bigger restriction on a stronger engine than they were on this one.  I was honestly surprised that the engine zipped right past 6000 - I think the mild cam was still happy in a RPM range that often causes stiffer sticks to loose control.

Joe-JDC

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Re: 428 Cobra Jet - iron heads, iron intake, cast manifolds - 450 HP on dyno
« Reply #2 on: February 21, 2014, 05:37:41 PM »
Barry did you run the engine up to 6000 with the headers?  If I am reading the chart correctly, it looks like you have 431hp at 5000 with the cast iron headers, and you said you had 434hp with the headers at the start.  Just how much are the cast manifolds losing to the top end?  I bet not much--less than 12-15hp?  Very nice build, and I am a bit envious of it up and running.  Mine is still on the stand.  LOL. 

Barry_R

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428 Cobra Jet - iron heads, iron intake, cast manifolds - 450 HP on dyno
« Reply #1 on: February 19, 2014, 09:39:27 PM »
Just finished up a rather interesting package.

Its a real 428 Cobra Jet.  Going into a numbers type of car, with a customer desire to hit 450 horsepower.  Seems easy - but...

The restoration nature of the car requires us to use factory iron everywhere.  Iron CJ heads.  Iron intake manifold.  Iron exhaust manifolds.  Stock oil pan.  Single point distributor.  Iron water pump.  And of course the factory 735 Holley carb.

The hope is that we could reach that goal on pump gas.  We went to a set of Diamond flat tops to get the compression up a bit - just under 11:1 - kinda brave for pump fuel but we are stretching and the customer is not against "spiking" the fuel if needed.  Cam is a custom hydraulic roller with duration numbers of 230/236 degrees at .050 and .559/.563 lift ground on a 112 LSA.  Did I mention the power brakes...?

We put bronze guides in the heads and did a multi-angle valve job, some modest bowl clean up & blending, and knocked the thermactor bosses out of the exhaust ports.  A similar light match & blend was done on the intake itself.  The block got a very careful round of torque plate machining, an upgraded ring pack, and some extra effort on getting things to turn smoothly.  Rockers are factory adjustables too....

Engine fired up nicely.  I started out with the headers just to get a feel for how it was going to run.  After warm up it went cleanly to 5000 making around 434 horsepower.  Knowing that the manifolds were mandatory I decided that we were OK and swapped over to the heavy iron.  We fabricated some extension pipes to get it connected to the dyno exhaust system, and even managed to get the O2 sensors connected for tuning.  I did use the points to trigger the dyno's MSD6 box since we were getting toward 6000 RPM.  I was VERY impressed that this basic ignition system pulled beyond 6000 many times without a hint of distress.

We made a bunch of full and partial pulls to find the best timing - which ended up with a total of 37, and fine tweaked the fuel curve by adjusting float levels and fuel pressure.  The basic jetting from Ford/Holley was spot on - I was just looking for incremental trends and gains.  Why?  Because it gave me multiple pulls of 447, 446, and even 448 horsepower.  I really NEEDED that 450 number  <img src="/images/happy.gif" height="14" width="14" alt="happy.gif">

And we did get it, with a peak of 450.3 at 5800.  It realistically flattened out at 5400 with 100 RPM incrementals from there out of 449, 449.5, 450.2, 449.8, and 450.3 horsepower.  Peak torque was at 479 pounds at only 3900 RPM - it had 464 pounds at 3000 and 408 at 5800.  The best air/fuel ratios on that stock Holley averaged 12.27 on the right bank and 12.57 on the left bank.  It dipped into the high 11s (rich) between 3100 & 3400, but stayed locked into the 12.4-12.9 ranges from there on up.  I've seen much more exotic carbs with much funkier fuel curves - them old guys in 1968 had this combo figured out very, very well.

Pictures, charts, and video follow.






http://youtu.be/7jQJLKWlbQI