408 rebuild

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itsfishy

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Hello all,

I have another thread going about my 408 getting extremely hot and I'm working on that issue, but in the meantime I'm considering doing a major upgrade to the motor to hit 500+ hp and am hoping to get some advice from builders. The motor is a 408, currently hits 408 hp at 4500 rpm on the dyno. It has ported iron heads, a Comp Cams shaft (287/305 duration, .497/.483 lift, 107 LOA), Eagle forged rotating assembly (Eagle 20502), Edelbrock RPM intake, and Holley 750 carb. I'm looking to switch the heads to Trick Flow Power Port 190 heads and the intake to an Edelbrock RPM Performer Air-Gap dual plane. Based on these changes alone, two of the horsepower calculators have put this build at just over 550 hp. My questions:

1. Any reason to change the cam from the current?
2. Any reason to change the rotating assembly from the current? I was considering going with a Scat assembly, but based on the results I'm reconsidering.

Other items you may ask:

Curry 9" rear
904 3-speed tranny
Melling hi-vol oil pump
MSD 6AL and Blaster 2 coil

I appreciate any feedback!
 
I don’t see a reason to change the rotating assembly. It’s forged, unless you are going to a light weight rotating assembly, crank and rods are all about survivability. What compression?
 
furrystump said:
I don’t see a reason to change the rotating assembly. It’s forged, unless you are going to a light weight rotating assembly, crank and rods are all about survivability. What compression?
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That was my thought as well, though I've found two different HP numbers for that assembly: one says good up to 500 HP (Summit), the other says good up to 700 HP (CNC Motorsports). Ironically the Eagle website doesn't give any specs. :rolleyes: Current compression is 10.5:1, I use 93 octane pump gas.
 
Eagle cast crank? I would definitely change it. Forged, I see no reason. Currently running Scat cast crank, shifting at 6500 crossing the stripe at 6800-7000, but a clock is ticking. I know practically nothing in regards to cams. I would call a reputable company and tell them what you have and what you are doing. See what they say.
 
If you plan on changing rotating assemblies I offer really popular 408" and 416" Molnar Technologies balanced rotating assemblies using ICON & Mahle pistons.

Cubic inch displacement can be changed around to support any bore size from 4.00" to 4.080". Your choice of compression ratio.

[FOR SALE] - 408" Molnar Technologies Complete Balanced Rotating Assembly for 360 Block - New

[FOR SALE] - 416" Molnar Technologies Complete Balanced Rotating Assembly for 340 Block - New

I have provided many members here on this forum and For B-Bodies Only with these assemblies.

Thanks,
Tom
 
furrystump said:
Eagle cast crank? I would definitely change it. Forged, I see no reason. Currently running Scat cast crank, shifting at 6500 crossing the stripe at 6800-7000, but a clock is ticking. I know practically nothing in regards to cams. I would call a reputable company and tell them what you have and what you are doing. See what they say.
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Yeah, crank is cast, everything else is forged. The 500+ hp numbers I gave on my initial post is at 6800 rpm so even though the specs are at 500hp/700hp depending on the source, it makes me a little nervous. What kind of power are you making?

I ran a couple of different cams through the calculators without any real difference in hp numbers, so don't know why the cam should be changed - but I'm a newbie at this so figured I'd ask.
 
PROSTOCKTOM said:
If you plan on changing rotating assemblies I offer really popular 408" and 416" Molnar Technologies balanced rotating assemblies using ICON & Mahle pistons.

Cubic inch displacement can be changed around to support any bore size from 4.00" to 4.080". Your choice of compression ratio.

[FOR SALE] - 408" Molnar Technologies Complete Balanced Rotating Assembly for 360 Block - New

[FOR SALE] - 416" Molnar Technologies Complete Balanced Rotating Assembly for 340 Block - New

I have provided many members here on this forum and For B-Bodies Only with these assemblies.

Thanks,
Tom
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Thanks Tom. I just looked over your link. I'll let you know if I decide to change them out.
 
If that is an Eagle cast crank I would change it. I would do nothing to make more power with that crank. I wouldn’t hesitate to go with Molnar. In fact, they are on my very short list.
 
If changing that much, maybe sell it and start fresh.
 
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furrystump said:
If that is an Eagle cast crank I would change it. I would do nothing to make more power with that crank. I wouldn’t hesitate to go with Molnar. In fact, they are on my very short list.
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Thanks. I was leaning towards changing it out to begin with.
 
The Eagle is fine for what it’s intended use is, but it is pretty easy to make enough power to get it out of its comfort zone. Also it is such a catastrophic event when they break.
 
According to a calculator 434 hp at the rear tire, but that seems a bit high to me.
 
itsfishy said:
I'm sorry - sell the motor? Or the internals? Finding a good 360 block isn't that easy these days.
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If you end up basically only keeping the block for your new build, and if you can get a decent price for the complete engine, probably go a long way at least towards the new short block you would think, just a thought.
 
furrystump said:
According to a calculator 434 hp at the rear tire, but that seems a bit high to me.
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The 556 hp (crank) was surprisingly high to me; at 15% loss that's 467 at the tire. 434 at the tire comes out to about 510 hp, which I think is obtainable with this setup though I'm admittedly basing that solely on magazine articles and dyno test videos.
 
273 said:
If you end up basically only keeping the block for your new build, and if you can get a decent price for the complete engine, probably go a long way at least towards the new short block you would think, just a thought.
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Gotcha. Well, if nothing else I can probably sell what's coming out of it and do an offset. If I were to take it in a whole different direction I'd probably look for a 383 block and stuff that in there. Technically they were only available in the Formula S package for 1967, but hey, it's still Mopar!!
 
Honestly, it’s just a number. In a well sorted car 500 hp will easily get you into roll bar territory. Not sure of your end goal.
 
furrystump said:
Honestly, it’s just a number. In a well sorted car 500 hp will easily get you into roll bar territory. Not sure of your end goal.
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Agreed, and the car already has a bar in it! Glad you asked though, because that really does make a difference. This car is mostly street, shows, that kind of thing. It may see the strip every blue moon or so. To be honest, I've been planning out a 500+ hp car for a while, but I'm now kind of wondering if putting $5-7K for an additional 100 +/- hp is worth it. I've got other things I want to do with it, so maybe I'll just postpone this for a little while. It really got me thinking about it when 273 suggested just selling this one and starting fresh. I may still do a couple minor things like changing out the intake for something that breathes better, but after chatting with you guys I might focus more on other things on my bucket list and worry about the motor somewhere down the line. Still, I appreciate everyone's input!
 
I agree with @furrystump on numbers being just that…. A number.

My 3200# duster that made 449 to the tire on a chassis dyno ran 10.32 @ 129 mph this weekend. On paper, the engine should make 600+ at the crank which would equate to 500+ to the tire which it didn’t.
 
I bought a 408 from Blueprint engines a couple of years ago. They use a 360 magnum block and modified Edelbrock heads with a hyd roller cam/lifters. At 10:1 it dynoed at 465HP and was a real runner. You can go to their website and look at that build to see what parts they use to get an idea. I matched that engine to a 727 and 3500 stall PTC 9.5 converter. Had quite a time keeping the power to the ground. Think in the end it is not how much power you have under your toe, but how much you can get (and keep) to the ground!
 
Ricks70Duster340 said:
I bought a 408 from Blueprint engines a couple of years ago. They use a 360 magnum block and modified Edelbrock heads with a hyd roller cam/lifters. At 10:1 it dynoed at 465HP and was a real runner. You can go to their website and look at that build to see what parts they use to get an idea. I matched that engine to a 727 and 3500 stall PTC 9.5 converter. Had quite a time keeping the power to the ground. Think in the end it is not how much power you have under your toe, but how much you can get (and keep) to the ground!
Click to expand...
I totally agree with you, and that's also part of the reason I decided to put this on hold while I finish up some other things with the car. At 20 -25mph it has no problems breaking loose if you hammer it in 1st gear (maybe even a little faster than that). Believe it or not, I was looking at the Torqstorm supercharger that would get it into the 650 range, but decided that probably wouldn't be very "streetable" and decided to aim for the 500s range. I might still go for the 500s, but I'll finish the other stuff first. Heaven knows I have plenty of other things to do.
 
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