Need 427 build advice - Chevelle Tech
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post #1 of 33 (permalink) Old Mar 25th, 20, 3:18 PM Thread Starter
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Need 427 build advice

I have searched through here a lot but have not found what I am looking for. I have 454 block, 6223 (366) crank to build a 427. I have a set of 781 heads with stock size valves. This is just a weekend cruiser mostly. I would like to get 425 hp at 6000 rpm or less. Can it be done using stock valves in the 781 heads? I would like to keep the compression around 9.5:1. Anyone got any links to similar builds or have input on what parts to use?
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post #2 of 33 (permalink) Old Mar 25th, 20, 3:36 PM
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Re: Need 427 build advice

They will support 425 hp with stock valve size.
Icon makes forged Pistons that will give you around 9.5 in comp with the 781s.
If it was me I would use a hyd roller cam on gen VI core so you dont need a cam button like this Lunati
https://www.lunatipower.com/voodoo-h...2-272-280.html
Make sure you use correct timing set of you get it on a gen VI core.
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post #3 of 33 (permalink) Old Mar 25th, 20, 5:21 PM Thread Starter
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The block I have is a Gen IV. Using a cam button is ok with me.
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post #4 of 33 (permalink) Old Mar 25th, 20, 6:56 PM
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Re: Need 427 build advice

If you're already buying new valves for the 781's, I'm betting it wouldn't cost much more step up to 2.19 intake and 1.88 exhaust valves. Of course how much more power you'd gain by installing larger valves depends on your cam choice, intake/carb choices and whether you decide to run headers.

Have fun with your build. The 427 is my all time favorite big block.
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post #5 of 33 (permalink) Old Mar 25th, 20, 7:11 PM
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Re: Need 427 build advice

Fairly mild build here. I did a recent build keeping the projected rpm lower that 5500. For this I chose 781 heads and did some work on the exhaust short side, smoothed out the guide boss and cleaned a little below the seats. I chose to keep the factory small valves but had them undercut. This is a 9.4 comp. 396 with the smallest voodoo hydro ft., 700 was the last 3 digits of the part number. Haven't completed it yet, cam they sent me had a broken dist. tooth so waiting on a replacement. I was going after off idle response in an automatic car so I hope my thought process pans out.
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post #6 of 33 (permalink) Old Mar 25th, 20, 8:05 PM
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Re: Need 427 build advice

About a 26cc dome piston will get you to the 9.5 compression area with the 781 heads. If your block has the cam plate holes already drilled you can use a Gen VI roller cam. I have a 1987 Mark IV block with the 6223 crank and dimple rods and Keith Black pistons with the 26cc dome, plus a set of 049 heads with 2.19/1.88 valves. The short block is assembled, heads have not been bolted on yet. I originally built the engine for my son, once completed he did not want the engine, I am considering changing the solid flat Xtreme Energy cam he put in the engine with a ZZ502 cam that was a take-out for a marine engine. My block will accept the Gen VI cam retainer plate so I can use the ZZ502 cam without a cam button.
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post #7 of 33 (permalink) Old Mar 25th, 20, 9:38 PM
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Re: Need 427 build advice

Quote:
Originally Posted by 454chevy View Post
The block I have is a Gen IV. Using a cam button is ok with me.

You can use the Gen6 cams in any block. They all have the two bolt holes for the cam retainer plate and it makes it all so much easier. You do need to use the matching timing chain set. There were a very few early 396 blocks that were not drilled but very rare and you can drill and tap them anyway.
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post #8 of 33 (permalink) Old Mar 26th, 20, 7:28 AM
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Re: Need 427 build advice

All good so far 454chevy. For the record, my Isky roller takes the 468 to around 6200, its 228/238, so you ought be looking for a intake lobe duration at around 220, and not much more for your sub 6000 rpm peaks.
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post #9 of 33 (permalink) Old Mar 26th, 20, 8:00 AM
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Re: Need 427 build advice

A friend built a 9:1 427 for his car hauler this winter. He used 781 heads with big valves and home porting. A Howards 120241-09 cam, rpm intake and 850 Holley. For fun we stuck it in his sons 67 Camaro. It ran 12.49 at 108mph.
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post #10 of 33 (permalink) Old Mar 26th, 20, 8:04 AM
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Re: Need 427 build advice

I would look for a factory 454 crank or just buy a new cast 4 or 4.25 stroke cast crank. You wont need as much dome to get decent compression and you get 30 more inches. That 366 crank must be balanced if you use it
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post #11 of 33 (permalink) Old Mar 26th, 20, 8:13 AM
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Re: Need 427 build advice

a 427-390hp L36 engine back in the day had 10.25 to 1 compression, a 214/218 @ .050 with .461"/.480" lift with a quadrajet, a modern intake and carb should get you close to the hp lost by lower compression so you need 35hp with a cam change assuming no porting on your heads, use one of those online cam calculators such as the one Compcams has
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post #12 of 33 (permalink) Old Mar 26th, 20, 8:32 AM Thread Starter
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I am not sure how to reply to individual posts yet. So I will group the all in one.
1. I may buy some stainless valves but would like to stay with the small valves. Don’t want to get into port work if I don’t have to at the moment. I don’t mind doing a little cleanup work though.
2. Good tip on being able to use the GEN 6 roller cans. Roller cam is the plan.
3. I don’t mind turning it 6200, just don’t want to go 6500+ rpm.
4. Just looking to do the old school 427. Always wanted one. I have never had a big block. Lots of small blocks though.

Lots of good info. Keep it coming.
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post #13 of 33 (permalink) Old Mar 26th, 20, 12:34 PM
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Re: Need 427 build advice

Keep the small valves spend the saved money on some good valve springs.
Clean up work is all the stock ports really need.. just blend all the stuff.

When Lingenfelter was around he wrote the larger 2.19-1.88 valves were good for 15 HP everywhere in the 781.
Pretty sure he opened the bowls to take advantage of the larger valve also.

You can get more from blending the bowls.
If you do not want to open the bowls larger then the larger valves will not work well.
Some 2.19 valves are very heavy and need a lot of spring pressure.
Not that you are revving it to a point of seeing.

I have went 12.5's with 1.72-1.50 valves in a 355" sbc and 230 at .050 cam with .480" lift 110 LSA 3300lb Nova.
Bowls blended of course.
Yes 1.72" intake valve.. Small valves do not scare me.
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post #14 of 33 (permalink) Old Mar 26th, 20, 6:34 PM
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Re: Need 427 build advice

I've "heard" big valves will also raise peak TQ by 500 rpms, so it may not even be advisable for your build. Agree with Jeff. And you dont need a roller cam to get your numbers, yet, you may want to spend the extra $$ on valve components like Jeff said. For reliability's sake.
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post #15 of 33 (permalink) Old Mar 26th, 20, 9:07 PM Thread Starter
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Re: Need 427 build advice

I will definitely be buying good springs and retainers to match the cam I use.
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