keith blacks

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mopar_1974

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well, i decided to add new pistons while im at it. I think keith black 107s

going into

1972 360
elelbrock air gap intake
holley 650 vac secondary
headers
comp cams XE274H K-kit cam, lifters, springs etc....
2.5 dual exhaust with H
stock 1.80 1.60 J heads

here are the questions
i called my engine builder and he said i might not be happy with the keith blacks due to the higher compression. i want around 10:1 with these
I should have no problem running premium pump gas right? any problems on streetability? I will most likely drive this quite a bit. What HP/TQ/1/4 mile can i expect and what will i gain by pocket porting the heads? any other pistons to consider? any suggestions?

1974 duster
727 tranny
b&m transpak
2400 b&m stall
 
I would change the carb to a 750 vacuum carb. The engine should make 420 hp or so and 400 ft lbs., but it's dependant on the gasket thickness that you'll be using and how much you plan on milling off the heads, if any.
 
The KB107's will require the block to be zero decked to bring the compression close to 10:1 and it will also require a thin head gasket. Just putting those pistons in a typical block with yield around 9.3:1, it will all be dependant on the volume of the head chambers and what machining you will do to the block and heads.

FWIW, I have a 360 with the KB107's and had the block machined for zero deck, it required about 0.020" be taken off the surface to do that. I am also using 64cc Magnum heads (J heads are around 72cc) with an 0.039" compressed head gasket, this gives me 10.6:1. I am using an XE268H cam but with the 1.6 ratio magnum rockers I have slightly more lift than the XE274 with 1.5 ratio rockers. Any case based on 1/4 trap speeds in the 102 mph region my engine is making around 370HP, I would expect yours to be similar to slightly less because of the J heads.

If your car is going to be primarily driven on the street do yourself a favor and stick with the 650 carb. I have had a Holley 600, Holley 670, Demon 725 and Holley 750 on my engine and the 670 was by far the best one. The driveability and throttle response is as good as the 600 and I do not feel a differnece on the butt dyno compared to the 725 or 750 on the top end. But the 725 and 750 definately loose a lot of throttle response at the lower rpm's.

BTW, all my 1/4 mile numbers are with the 600 and the best time is 13.7 @ 102mph with a miserable 2.2sec 60'.
 
yeah, im sticking with the 650, ive already got it

still a few questions.
I should have no problem running premium pump gas right? any problems on streetability? I will most likely drive this quite a bit. will i gain by pocket porting the heads? any other pistons to consider?
 
i got 355s in my 81/4 to tell you the truth if your doing much highway driving 65-70 mph then i'd go 323 i run 2900 rpm @ 60 with the 355s but cruiesing around towns okay and pulls good at the track i'd still get your block zerodecked or your just defeating the purpose of them pistons it'll still run on pumpgas
 
That's nearly the identical build I have in my 68 Cuda. 360 w/kb107's. X heads pocket ported and port matched and polished chambers. Apparently my heads were milled quite a bit before I got them cause they cc'd at 66 cc so the final compression is 10.21 to 1 with a .027 gasket and the pistons .021 in the hole. 274 xe cam. Hooker headers. Air gap intake. 750 holley vac. sec. 2800 stall. 4:10 gears (hate em. Way too low for street cruising, switching to 3.55's ASAP). Runs fine on pump gas. Never a sign of spark knock.

Haven't been to the track with it yet. Just got it together a little over a month ago. Runs real strong though.
 
awesome fishy68, great minds think alike. i want a good flat 10:1. id rather be running a 2800 stall but i couldnt beat the price on the 2400 that i got. I just picked up richmond 3.55 gears for my 8.25 for $25 shipped! only 800 miles on them. cant beat that either. let me know the times when you run it down the track, im curious on what mine will do.
 
mopar_1974 said:
id rather be running a 2800 stall but i couldnt beat the price on the 2400 that i got. I just picked up richmond 3.55 gears for my 8.25 for $25 shipped! only 800 miles on them. cant beat that either. let me know the times when you run it down the track, im curious on what mine will do.
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Some good deals there. That's the way we like it. Wish I could find a good set of 3:55's for that price for mine but looks like I'm gonna have to go new. Hopefully in the next month or so I'll make it to the track and I'll let you know how I did.
 
dont know your cam profiles but if you run into detonation problems you can extend duration to bleed off cylinder pressure.
 
hmm, now that i am looking at around 400 hp, is my 8 1/4 gonna hold??? Im putting 3:55 richmond gears in with a sure grip, what am i going to look out for and what can i do to beef it up some more. i heard they will hold up to 400 stret hp but this is right at the edge
 
they will hold more and thats what kind of hp im going for sept i have the chance to get a 4 speed setup minus the clutch for like 1000 but i think im goin to stay auto
 
If you have 10:1 compression, please dont put nitrous on that. Nitrous creates more heat and in turn more load on the piston. At the very most compression you want with nitrous is 8.5:1.

Talking about the rearend, they can handle more then 400hp with a fully built unit. New bearings, ring, pinion, posi unit, clips and everything.
 
DusterBoy15 said:
i thought i saw a link were it held like 600 or under not sure
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There was an article in one of the mopar magazines a couple of years ago about building an 8.25 and they said 600 with a sb. BUT, it required better axles, a diff like an Eaton or Auburn, careful set up and a rear cover with the bearing support jack screws.
 
You can use nitrous with 10:1, I have used it with 10.5:1, That being said it would depend on how much nitrous you can add safely. With compression in the 10:1 range a 100hp kit is about as high as you want to go. Nitrous is like supercharging in a bottle and can be used at higher compression ratio motors in moderate levels or better with fuel quality.

Chuck
 
mopar_1974 said:
nitrous creates MORE heat? i thought it did the exact opposite and raises compression by lowering heat
Click to expand...

No, all it does is lower the intake cahrge temp, The chamber temp will go up because there is more O2 and fuel in the same space, and it will really go up if you lean out and that's part of what eats engines.
 
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