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Couple questions for the BBC guys

  
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Couple questions for the BBC guys

 
jumbo2 jumbo2
I love my Chevy Chevette! | Posts: 5 | Joined: 10/12
Posted: 10/28/12
07:45 PM

My build so far 454 -.30 over with forged 27.5cc dome pistons
                       -truck rods with arp bolts
                       -cast crank 10 under and arp mains
                       -edelbrock rpm air gap dual plane
                       -hooker ceramic coated big tube headers and mandrel 3"
                       with single chamber mufflers
                       - 825 cfm race demon
                       -full msd pro billet dizzy and digital 6 box


 next step is the heads , after much debate budget vs aluminum heads Im going to rebuild my oval port 781's. When I take my 781 oval ports to the machine shop to have them freshened up should I just replace the valves with SS undercuts or go with bigger valves ? And with these heads and pistons my comp ration should be 9.8:1 so should I shave the heads to get right at 10:1 so its pump friendly ?



My goal is to get my 3800lb c10 shortbox into the mid 11's , Its not a daily driver and will see some summer street fun and friday night drag time and it souldnt be hard it has a 4000 stall and a trans brake running to a ford 9" and 33/18.5/15 tires I feel the converter is a bit high but it actually drives very nice on the street but am thinking a 3200 would be better suited , the 4000 converter was in truck when I got it , I have some comp roller lifters and was leaning towards the comp cams  x energy 274 hyd roller as my dyno program seems to make me believe the tq is over 400 ftlbs from 2000-5000 and peaking at 545ft lbs and hp around 475 at 5750rpm and my limit would be 6000rpm to make it last

thanks for the help  

pepsi1 pepsi1
Big Block power for the win | Posts: 940 | Joined: 03/11
Posted: 10/28/12
08:32 PM

Jumbo2:
Lets take the heads first. If you stay with the stock sized valves, they will be no advantage to installing and spending money onSS valves. Heres why.

1.Install the bigger valves, if you are good with a die grinder, don't have the machine shop finish the valve job in the head. Have him leave the rough cut, get in there with a die grinder and blend the bowls and the floors of the intake and exhaust valves. Then Gasket match your intake manifold, at the same time. I said this just in case you nick a valve seat with the die grinder.
  Then have him do a 3 angle valve job.
1.45-degree main seat cut  
2.30-degree top cut
3.60-degree bottom cut
4.Then a 70-degree cut to blend it into the port.
5.I'm sure an experienced head guy will know what to do. I only mentioned this so our younger Gear Heads get an idea of what goes into a 3 angle vale job. There is much more that can be done, but with the peanut heads it really won't help for the time and money involved...

  If you want to up the compression use a steel shim head gasket. Just apply 2 light coats of Aluminum spray paint. Let it dry between coats.
  You can use a $2.00 can of Aluminum spray paint. You don't need to use the expensive gasket sealer. Just torque the heads in the proper manner.
  If the heads are not flat then you can trim off .010 to .020 and resurface the heads. I'm going to continue this on another reply post.

Bob  

pepsi1 pepsi1
Big Block power for the win | Posts: 940 | Joined: 03/11
Posted: 10/28/12
09:12 PM

Jumbo2:

You have a nice package for torque and Horse Power. You didn't mention what rear gear ratio you have? I like the idea fo the Ford 9"...

That cam you are talking about is the mechanical roller XR274R is that correct? Thats a nice tight lash cam. That will snap your neck!
 
  The 4000 stall convertor with a 33" tall tire you will need a 4:30 to 4:56 Rear Gear, to bring the RPM where your power band will be. The only bad part about that you will run out of top end RPM. Even though the Cam Specs from 2200Rpm to 6200RPM. You don't want to spin a cast crank any more then 6500RPM MAX. Unless you just drop to a 2600 to 2800 rpm torque convertor as you said.
  You need to be up there so it will idle in gear. That would be the way I would go. With a 3:90 to 4:10 Rear Gear Ratio. That's a well thought out package. Just work on the heads.
  I don't know if you have used ARP Fasteners before. But follow their specs for torquing all their fasteners. I can't stress that any more. Use the proper lube for them also.
  (I would look further down the road for a 700R4 or 4L80E trans). Then you will have a nice O/D.
  I just want to make sure of the cam. It's a Comp Cam P/N 11-770-8-(10.46)
the grind # XR274R Solid Roller....
Specs are.  Lash set Hot.016in/.018ex .236/.242 @ .050 .639/.646 lift
Jumbo it really sounds like some fun.... Grin  Cool
  But to get a 3800lb truck into the 11 Second range you will need a combination of approx 675 to 725 horse power. On a Tunnel Ram with maybe juice. (Something I don't like). You have your program run some numbers and see if I'm close. With 650HP as a Min. Good Luck...

Bob  

68scott385 68scott385
I have an SS396 tatoo | Posts: 325 | Joined: 07/09
Posted: 10/29/12
07:48 AM

IMO, the 9.8:1 is more pump friendly than the 10:1.

Bob's right about using a shim gasket to boost compression a little.

My dyno program  leads me to the CC XR276HR so if you're going mechanical roller I'd say you've found your cam.

I think Bob hit the gear ratio right on the money too with a 4.10. I had a 67 C20 w/383/700r4/4.10/31" tires. Couldn't get traction on the starting line. The tires we're not meant for race on asphalt/concrete either.

If you do get a 700r4, make sure it is built to handle what you're asking it to do.

If you want aluminum heads, the AFR 290-O look as good or better than any other oval port head.  
68scott385 68scott385 68scott385

jumbo2 jumbo2
I love my Chevy Chevette! | Posts: 5 | Joined: 10/12
Posted: 10/29/12
09:13 AM

Thanks for the Great info BOB , what size valves would you recomend ? You mentioned peanut heads but these are not peanuts the 781 ovals . So would the be a point going from 9.8:1 to 10:1 ? If I do install the big 2.25 intake will I have to notch the cylinder for room or is that only a big valve on a 396 cu ?  

68scott385 68scott385
I have an SS396 tatoo | Posts: 325 | Joined: 07/09
Posted: 10/29/12
02:00 PM

Factory heads are either 2.06/1.77 or 2.19/1.88. You can fit the bigger valves in a standard 454 bore without notches.  
68scott385 68scott385 68scott385

pepsi1 pepsi1
Big Block power for the win | Posts: 940 | Joined: 03/11
Posted: 11/02/12
09:08 PM

Jumbo Sorry I haven't around been busy with other things.

Your welcome.
I know the a pain. Yours is not notched. See if the smaller of the factory valve fits without any problem. I'm not sure when you went to the peanut head,if it changed the oriantation of those valve. I would put the smaller of the two in both the intake and exhaust. Unless the guy at the machine shop may have a set of the bigger valves he trashed and he may give you for a cup of coffee. Then just use the inner valve spring and you should be able to see the clearance with the valves at max lift, and you look into the intake and exhaust ports.
  If you need to notch the block you have to purchase the correct head gasket with the notch. You can use that as a template.
  I personally don't think the biggest valve will help.The flow is not there with those heads.9:8:1 is a good compression you the gas today. Let us know.

Bob  

jumbo2 jumbo2
I love my Chevy Chevette! | Posts: 5 | Joined: 10/12
Posted: 11/03/12
07:54 PM

I never went to a peanut head , I have 781 oval port 118cc chamber  

shumate88 shumate88
I love my Chevy Chevette! | Posts: 5 | Joined: 11/12
Posted: 11/18/12
09:46 AM

Jimbo
I had a set of these on a 70 Nova with a 432 (427 + .030).  I did the valve work Bob is referring too.  If your machine shop uses Serdi tooling, it is capable of 5-6 angles on the valve.
This engine and head combo in the Nova with a full stock frame with connecters and a ladder bar set up ran 6.30's in the 1/8.
These heads can be made to work very well, I have found that the oval ports allow you to keep the velocity up and work well with a variety of cams.
A similar set of these heads are going to be used on my up coming 427 build for my 68 Camaro.
Hope this helps, just trying not to confuse you.