451 build

[747mopar]

I've noticed there are allot of guys hear that really no there stuff (which is why I joined) so I thought I'd run this build by you. Wanting a good street motor for a low cost I decided on a 451, I used a 73 400 block and a forged 440 crank. I had the mains turned down and did the clearance work myself then had the rotating assembly balanced. I went with KB pistons and had the dome milled to a flat top and the block ground to zero deck height. The rods are 440 rods that now have floating pins. I went with 452 heads because they are supposedly friendly to amateur porting, flow well and with the hardened seats they are a little cheaper to build. The valves where shot so I had 2.14 1.81 Ferra valves installed with a three angle valve job, bronze guides, comp springs etc. I ported them myself and then had them flow tested just to make sure I didn't ruin them. Everything figured in the ratio comes out to 9.8:1. For a cam "this is the spot I struggled with" I went with Comp Cams 21-224-4, I didn't like the idea of running allot of stall or tall gears and this cam puts me in the rpm range that I will likely be cruising. For rockers I went with Comp Cams Magnum rockers. Induction is a Performer RPM and an 870 Avenger. For ignition I went with a Mallory 6AL. I will be running Hooker Super Comps 1 7/8 with a 3" exhaust.

 

[RustyRatRod]

Get ready to spike it with race gas. I don't think that's enough cam to run completely on pump gas with iron heads. I like the build though. I just don't think you'll be able to put any timing in it worth a snot without detonation. At least on pump gas. I'm building a 383 with 10.4:1 with iron heads and quench. The cam I have is 271 @ .050. The point of a big cam with a high static compression is two fold. It'll make more peak power, plus it will bleed of cylinder pressure if you want to run on pump swill. If yours doesn't rattle, I'll be surprised. I think you need a good bit more cam. I could be mistaken, but that's just my honest opinion.

 

[tallhair]

Get ready to spike it with race gas. I don't think that's enough cam to run completely on pump gas with iron heads. I like the build though. I just don't think you'll be able to put any timing in it worth a snot without detonation. At least on pump gas. I'm building a 383 with 10.4:1 with iron heads and quench. The cam I have is 271 @ .050. The point of a big cam with a high static compression is two fold. It'll make more peak power, plus it will bleed of cylinder pressure if you want to run on pump swill. If yours doesn't rattle, I'll be surprised. I think you need a good bit more cam. I could be mistake, but that's just my honest opinion.

that makes sense but is contrary to what i would have thought.

 

[lewtot184]

iron heads, almost 10:1 (this is a clean combustion chamber, will be well over 10:1 with some carbon build up), short cam, and no quench; won't live on pump gas. you probably would have been better off leaving the quench domes on the pistons and choosing a mechanical cam with an asymetrical lobe so could juggle the cylinder pressure a little. non-quench engines aren't pump gas friendly unless the compression ratio is down.

 

[747mopar]

Get ready to spike it with race gas. I don't think that's enough cam to run completely on pump gas with iron heads. I like the build though. I just don't think you'll be able to put any timing in it worth a snot without detonation. At least on pump gas. I'm building a 383 with 10.4:1 with iron heads and quench. The cam I have is 271 @ .050. The point of a big cam with a high static compression is two fold. It'll make more peak power, plus it will bleed of cylinder pressure if you want to run on pump swill. If yours doesn't rattle, I'll be surprised. I think you need a good bit more cam. I could be mistaken, but that's just my honest opinion.

Hears my problem, the bigger the cam the higher the rpm where it begins to make power which is the problem for me. I'll admit I don't fully understand the relation between quench and detination although I do understand how a big cam will bleed off compression. I honestly thought 9.8:1 would be safe. Hopefully I'll get it fired up in the next couple of weeks. Thanks for the input

 

[lewtot184]

you can always think about using a cam with a wider lobe separation to close the intake valve later.

 

[19polara64]

Cometics make thicker head gaskets if you want to lower your c/r.

 

[SwedCharger67]

Hears my problem, the bigger the cam the higher the rpm where it begins to make power which is the problem for me. I'll admit I don't fully understand the relation between quench and detination although I do understand how a big cam will bleed off compression. I honestly thought 9.8:1 would be safe. Hopefully I'll get it fired up in the next couple of weeks. Thanks for the input

I had the same 21-224-4 cam in my 383. My engine had the 346 heads, very similar to your with RPM intake, Hooker, Holley 750, stock converter, some 2.91 at rear if I remember correctly.
That cam wasn't working so well in my 383, probably because of the extremely low static compression, less than 8:1. With the intake valve closing at 63 degrees ABDC it gave a dynamic compression of around 4.5
The engine was powerless, vacuum was low (around 8 in), very difficult to get idle correctly tuned.

The sound though was very good, but power was down. I believe with your higher compression, and bigger cubes, it will work a lot better. I'm actually thinking of re-using it in my new 512, I think it'll do a good job there (E85 engine with 12.4:1, 7.5 dynamic).

Also, with the late closing intake valve, my guess is that detonation with that cam won't be a big problem.

 

[Garys1969RR]

My son is running that same cam in a 70 Super Bee, 915 heads, Street Dominator intake, 3.91 gears. 12.5 to 1 C/R. And that thing hauls A_ _! Of course he has to run 100 Octane Sunoco. He can almost keep up with my 451 RR! Of all the motors I ve ever built, only the ones with lotsa C/R made any significant power. Just be prepared to use a little octane booster of some sort. Like 50 50 with 100 Sunoco. Or whatever ratio works for you.

 

[747mopar]

After reading your replies I educated myself "if you want to call it that" on detonation. I have a better understanding of what it is, what causes it and what can be done to keep it at bay. I also learned that a 25 degree decrease in air inlet temp can be good for one octane point, keeping the intake itself cool will help, a good coolant system will also lesson the chances, etc. These are all things I've already addressed, my charger has a shaker hood, I have a be cool aluminum radiator with a high flow water pump and electric fan, I also blocked off the heat transfers on the intake. I also read that a good ignition helps as well, I'm running a 6 AL. If it does detonate I saw a dyno test regarding advancing the cam, it made a little more power but making the intake close a little later might be a possibility or am I wrong. Thanks for the feadback

 

[383man]

Any way you could consider running a closed chamber aluminum head ? That would give you quench with a .039 head gasket. And aluminum disapates heat better. With the open chamber head you have its hard to get quench (getting the piston about .045 away from the head) but as stated a cam that drops the cylinder pressure would help. Ron

 

[747mopar]

I would love to but refuse to put Chinese parts on my car and can't afford the Edelbrocks "YET".

 

[RustyRatRod]

Oh and one more thing. Unless you had hardened seats installed, you don't have them anymore.

 

[747mopar]

Oh and one more thing. Unless you had hardened seats installed, you don't have them anymore.

Damn Rusty are you just trying to burst my bubble. No in all honesty I thought the same thing and did my research and yes I still do, at least according to my machine shop and Muscle Motors who happens to specialize in Mopar High performance. When I'm in doubt I talk to them because they do big block Mopars everyday for all applications and no there stuff. Thanks though

 

[RustyRatRod]

They were induction hardened. They are not inserts. The hardening only goes down about .010-.020". Trust me, it's gone. It aint a deal breaker. Don't worry about it.

 

[747mopar]

I know they aren't inserts, no nothing about the depth. I just figure the guys at MM must have done it before because they are certain they are fine. On the other hand I have two friends running 906's without inserts, don't know how long they will last but they've lasted several years so far. I remember when I was talking to my machine shop about 906's he said I'd only need seats for the exhaust but would probably be fine if I ran stainless valves "why" I don't know. I do have stainless ferra valves though. If your correct then I'm a little ticked seeing how I was misled twice.