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apexrig1 10-04-2012 07:06 PM

Want more power out of 427
Hey everybody I have a few questions in hoping you can help me with. A friend of mine currently has 427 bbc that ran 520hp on the dyno. Now after a few years he wants more power closer to 650hp. No nitrous. He is on a very strict budget. Now the motor has forged crank and forged domed pistons. Now I thought in my mind he could disassemble the motor have the pistons milled down to be flat tops giving it around 8.5:1. Put a weiand 177 blower ontop. Possible upgrade to a hydraulic roller.

Would this work? If not could I get input on what you guys would recommend? This is strictly a street motor in a 71 gmc half ton.

Thanks a bunch

vinniekq2 10-04-2012 10:11 PM

Depends on what is already in the engine. What heads are on the engine at this time? 650 HP is easy with a blower/turbo and 575 is very street able in normally aspirated.

SSedan64 10-04-2012 11:35 PM

If the Domes are solid they can probably be milled down enough. If they're hollow Domes no go. 10-05-2012 05:11 AM

Most 427 BBC high compression pistons can't be cut to flat top safely.

AutoGear 10-05-2012 08:12 AM

When you say strict budget, what do you mean? To me, "blower" and "strict budget" don't go together

apexrig1 10-06-2012 12:22 PM

He has the 781 oval port heads. They have been ported with 2.19/1.88 valves.

I can't see it being very expensive to do that's all. Because all he needs is to lower the compression change cam and stick the little weaind 177 on there? Or am I missing something?

Is there a way to tell if the done is hollow or not??

vinniekq2 10-06-2012 12:26 PM

who wants the blower,you or the owner? a better set of heads will add 60 plus hp

apexrig1 10-06-2012 12:34 PM

He is just looking for a way to get around 650hp or so and we figured this would work fairly good.

Can a person get that high with just changing to better heads and upgrading to a hydraulic roller? It's currently a solid flat tappet
right now.

F-BIRD'88 10-06-2012 12:50 PM

Getting a 520hp 427 to a true 650 HP level is not going to be cheap.
ALL the 520hp parts will need to be changed to parts Capable of 650hp. Induction/valvetrain/exhaust/heads

A true 650hp N/A 427 is fairly radical and will not be cheap.
Get a better job and or buy a nitrous system. easiest cheapest way to get from 520hp to 650 hp.

If you really want that much more power N/A build a large CID BBC. 496++CID + solid street roller cam big carb fully ported heads or aftermarket aluminum.

If you want to supercharge it change the pistons to lower the compression ratio.
7.5:1 for max performance with a roots style blower and premium pump gas.

650+ superchaged power from a low compression 427 is quite possible.
177 blower and 950-1000cfm carb or bigger 671-871 style blower + two 750's or a Procharger/Vortech centrifical.
New blower friendly solid street roller.

Hyd roller cams in a BBC are for the girlie man . (especially on a blown BBC).

A N/A street strip 650HP 427cid BBC that runs on pump gas would look like this.
Fully correctly ported oval ports. true 10.5:1 cr. Comp XR286R-10 cam or XR292R-10 solid street roller cam.
(or similar 248 to 260deg solid street roller cam .650+lift) with suitable valvetrain.
Vic JR/ Holley strip dominator oval port single plane intake 950-1000 cfm carb. Or a BBC street tunnel ram and two 750's
Big tube 2"+ headers
92+ octane gas
8" 10" 4000+ stall converter and correct gearing.

Just cause your oval port heads are ported and have big valves does not mean they are working.
They probabily need some more attention to get them right.

Again nitrous is the cheap path to big power gains, at low cost.
Beyond this there is nothing cheap about 650hp.
Does your buddy actualy have a use for a real 650 horsepower ? (actually race it)
Or is just a POSER with no money and big dreams.

What is the current engine combo (details). What is the budget?
There is probaly lots of room for improvement on the current combo for more than the
present 520HP.
Has this truck ever been drag tested to establish the real performance level?
What is the performance gain goal from this point. Beyond "I want a 650hp tuck"

my87Z 10-06-2012 01:07 PM


the reason most people are saying that going the blower route will be expensive is for 1 the blower is going to cost 2500+ to get it delivered. Then I would say that it would be a little dumb to run a blower on facotry heads (just my opinion) and I'm not sure those heads in the shape they are in can even support 650hp. So there is a set of aftermarket heads, 1800-2500. To do this he is looking at 5,000 easy, and that doesn't include the machine work to the pistons (i'd just buy new pistons).

Since this is a 427 BBC which is basically the same block as the 454 BBC just with a 396 crank, I would say go after building a 496, he'll have about 2500 into the rotating assy and the machine work. Then go after the aftermarket heads, and probably another cam. It isn't too hard to make 600-650hp out of a 496 (with the tq to match). Then later on if he decides he wants even more then he could toss a blower on it and be in the 750hp range (suposing the block and other parts hold up).

vinniekq2 10-06-2012 01:26 PM

my87z is correct
what I said,heads = 60 plus hp.50 cubes will add 60 plus hp,torque would go up.

or like I said 60hp for better heads and maybe 20 more with a roller cam,thats 600,,,
blower or 496 will both need new pistons.
do the math on the cost of parts and see what works best for the situation? a 496 can use bigger heads than a 427 so more power potential there

68NovaSS 10-06-2012 01:35 PM

Doesn't seem reasonable to expect 650 out of a little 177 and 427 c.i., that's JMO>...

techinspector1 10-06-2012 01:55 PM


Originally Posted by (Post 1596272)
Most 427 BBC high compression pistons can't be cut to flat top safely.

I agree. I'm no engineer, but from what I've been able to put together over the years, good engineering practice dictates that the crown thickness will equal about 7% of the diameter for a naturally-aspirated piston. The crowns on dedicated blower pistons will be thicker than those on naturally-aspirated pistons, so you would want to be adding material, not cutting material away. I don't know what the percentage of crown thickness to diameter would be with a dedicated blower piston, but common sense tells me 8% to 9%.

F-BIRD'88 10-06-2012 02:05 PM


Originally Posted by 68NovaSS (Post 1596623)
Doesn't seem reasonable to expect 650 out of a little 177 and 427 c.i., that's JMO>...

This 177 blower is fully capable of this power level on pump gas with healthy 10PSI boost.
2.33:1 drive ratio. Even on a SBC.

on a 427BBC w ported big valve oval ports its no sweat.
Low compression, 7.5:1 suitable street solid flat tappet or solid street roller cam.
248 to 255@.050" duration.
big carb. 2.33:1 drive.

A Comp XR286H-10 cam or a custom blower version of this cam ground on a 112-114LSA will get it done with the 177 on a 427BBC.

Lunati street roller cam #502A3LUN would be another example
Lunati flat tappet cam #402A4LUN will get it done very nicely on a budget.

A hyd cam or a hyd roller cam will really limit this motor.

lowering the compression is easy on this motor. Just replace the pistons with 427 forged flat tops.
Or get a 454 crank and use Common low cost forged L2377 454 flat top pistons.
Picking up 20cubes is a bonus.

this motor will easily make 650 hp with a 177 blower but I would get a Weiand 8-71 and two 750 edelbrocks for it on this motor. (+ the solid or solid roller blower cam)

( bet this motor has a lame hyd cam in it now and that is a big part of the current HP limitation problem.)
Cutting the dome of the present piston would be a big mistake.

67-4-fun 10-06-2012 05:38 PM

I would swap out the camshaft for something like this one from Lunati Street Strip Hyd Cam - Chevrolet Big Block 285/295 - Lunati Power then buy you a 100-150 shot cheater nitrous system, good street motor then nos if you go to the strip.. 100-150 is pretty mild shot for bbc.. this setup may cost you less than $500-$600 you get the power you want and have fun for lot less than a 2 grand blower adder not blower wouldnt be cool, but i think you dont have the right SCR or the right setup for it, NOS just bolt on and go once you learn a few detail before you run it, not hard, just common sense

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