Kaase P-51 Cylinder Heads



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Product Description

P-51 aluminum cylinder heads for Ford 429/460 big-block engines, the 385 series.

Earlier this decade, Kaase demonstrated their considerable engine-design talents when they corrected longstanding failings in the original 385-series cylinder heads. The engine’s potential was finally realized when Kaase relocated the valves, redesigned the combustion chambers, and reconfigured the internals of the intake and exhaust ports. For the first time, the 385-series engine exceeded the 350-cfm peak intake flow of the desirable Boss 429. Kaase with Ford designated the new heads the Super Cobra Jet.

The P51

In the intervening years and with ambitions to expand into broader markets, including the street performance arena, Kaase consolidated the gains made in the SCJ heads and continued to refine them. Now, with peak intake flow ratings of around 400-cfm, the new Kaase P51 variants are available directly from the Kaase factory. Of perhaps greater significance is their superb mid-range flow characteristics (see table below).

Commendably, Kaase retained the 72 cc combustion chambers, which allow users to run pump fuel. This chamber size also permits experimentation with different compression ratios: employing slightly dished or slightly domed pistons as desired. Importantly, the P51 chambers are fully CNC-machined, and contain larger 2.250-inch intake valves. The standard size exhaust valves are retained. The P51 heads function with the original rocker gear, but require longer pushrods because of altered valve geometry. For convenience, intake and exhaust port locations are unchanged.

Kaase P51 flow chart (at 28 inches of water) reveals exceptional mid-range flow

Valve Lift (inches) Intake (cfm) Exhaust (cfm)
0.100 72 52
0.200 152 107
0.300 234 151
0.400 306 183
0.500 350 202
0.600 368 215
0.700 388 229
0.800 395 239



June 6, 1978. Wednesday night match race at Raceway Park, Englishtown, NJ. All the heavy hitters were there. At this time no door slammer had ever gone quicker than 8.01. Mountain motor match race pro stock cars were the fastest of any car at this time as Pro Mod was a good bit in the future. The weather was perfect and everyone knew what was coming. First round Dyno Don Nicholson cranked off a 7.99 second run to become the first in the sevens. Nicholson was fiercely competitive when it came to match racing. I swear he would rather beat Bill Jenkins or Ronnie Sox two out of three at a match race than win a NHRA national event. Even though we won the NHRA Pro Stock world championship the year before, I think this 7.99 run may have been our finest moment as a team. For myself, after thirty eight years of building racing engines, this still rates at the top.

Well, you’re saying “what’s your point”? My point is, it was done with a lowly 385 series Cobra Jet. The engine was a 516″ Can-Am aluminum block Cobra Jet, which was considered huge at the time. The cylinder heads were Ford Engineering, aluminum SCJ reproductions. Basically, they were just like the D0OER heads, only Aluminum. Another career highlight though, would be winning my first Enginemasters with a 468″ SCJ.

I have a thirty year history with the 385 series cylinder head. I still love to rework them and try to improve the 1969 design. In 2001 we redesigned the porting and valve positioning and came up with a completely new SCJ head. Partnered with JMP in California, We produced the first two thousand heads for Ford. After two years the project came up for re-bid. A company in Detroit out bid us by enough that we were forced out of the project. I had to accept the ways of big business and still continued to buy “our” head from Ford. During the last two years we have been improving this head even more. JMP has built new patterns and tooling and we have, over the last year, spent countless hours’ dyno testing different combinations. We have focused on the 466 and 514 engines with numerous cams and intake manifolds being tested.

So what’s the difference between this new P-51 head and the Ford Motorsport SCJ? First we made some changes in the chamber and then had them CNC machined so they would all be the same. Then we made some changes in the water jacket to allow for more aggressive porting at the intake short turn and left side wall. When porting the SCJ’s, many times we would run into water above the intake seat, close to the top of the short turn. We then set up a program to CNC under both seats, down in the bowls and to the top of the short turns. The goal is to flow about 400 cfm on the intake, 250 on the exhaust. The real magic in this head though, is the intake flow at .400″ and .500″ lift.

One of the big complaints of the SCJ head is that some of the rocker arms don’t meet the valve tip correctly. Also, if you use longer valves for more spring height, the problem gets worse. We have changed the rocker stud angles and positions to accommodate most rocker arms and valve lengths. Yes, new stud girdles are being made at Jomar. We are also having .100″ long, custom valves produced.

The valve guide angles and locations are the same as the Ford Motorsport SCJ’s. The pistons usually don’t need an exhaust valve relief, while the intake relief will almost never need to be deeper than .150″. The intake face, exhaust face and the valve cover surface are also the same as the SCJ’s.

Notes on Airflow

I hate flowbenches. As you may know, most of our work is with 815″ Pro Stock engines. On these heads the flow bench is almost totally worthless. I think it’s misleading at best. We can port an older aluminum A-429 CJ head to flow 400 & 250. Then we can have a P-51 head that flows the same. The P-51 will dyno75HP better than the CJ. It’s all about sizes, areas, shapes, and valve placement in the bore. I think you’ll find that the more an engine builder uses the dyno, the less he trusts or even uses the flowbench. There are so many flowbenches out there in use that almost everybody thinks he’s an expert.

One of our main goals when engineering these heads was to be able to deliver them with 400 cfm intake ports. We have reasonably well achieved that goal. In high flowing intake ports with the port opening positioned down close to the head gasket surface, the air often breaks away from the port floor and results in turbulence. This usually occurs above .600″ valve lift when the air flow is high. With the P-51 head, some of the intake ports will be smooth and quiet all the way to .800″ lift. Those ports will usually flow over 400 CFM. Some of the ports will go turbulent at .550″-.650″ lift. When it happens, the sound changes and the airflow will drop off about 20CFM. The flow will be the same or better than the well behaved port right up to the lift where it goes turbulent. There are several ways to fix this, all of which are not a good idea. If we raised the port entry about 1″ at the manifold, it would be a big help because the air would not have to make such a sharp turn. Of course none of the manifolds would fit. If we made the port a lot wider or taller at the short turn, that would fix the problem because the air speed would be much slower. But slow is not what you want in a good performance or race engine. When flowing one of these problem ports, sticking a butter knife or blade in the floor of the port will usually straighten it out to flow 400. We have dyno tested engines with heads that flowed 400 and then changed to heads where every port went turbulent to flow 375. They both made the same power. Now, if you ran a set of heads that flowed 375 because of improper porting or seat work, and then reworked them to flow 400, they would for sure make more power.

At the 460FORD.com engine tech seminar in Owensboro, KY, I had a client tell me that he replaced a set of A-429 heads (Ford aluminum Cobra Jet) with P-51’s. He was thrilled to have a 100HP increase! I think this would be on the high end, but I think 75 would be realistic if it was a good, sound engine with at least 256 degrees of camshaft. We have run enough different combinations to be able to say that a well prepared 466 will make about 700HP. A 514-521 will make 800HP. This would be with as delivered P-51 heads, at least 256 degrees of roller cam, an un-modified Edelbrock Victor 460 (or Ford counterpart) and a Dominator type 1150 carb.

The assembled heads have top quality parts. We had the valves made to our specs. They are .100″ longer than stock for more installed height. The valve springs for the roller cam heads come from Manley (#221443). I have used these springs for years on drag race, oval track, and even the Enginemasters entries. They are very expensive, and I had to think long and hard about risking a cheaper spring. The best choice won out because I didn’t want anyone losing engine with us saving a few bucks on valve springs. The spring locators, steel retainers and locks are from Comp Cams. The rocker studs are ARP Pro Series.

The bottom line is this: this is the best flowing, most powerful, user friendly 429-460 wedge head out there. I have put my heart and soul into this project, and if it has my name on it, it’s going to be pretty damn good.

Jon Kaase