xbgt74

What size power valve do you reckon i need to put in my 950 holley.....the motorr is a 408 stroker with afd alloy heads ...12.5 comp...270@.050 custom cam.It idles at 1300rpm.It currently has a 45 power valve in it.As you drive along it sees about 10'' vacuumn.The motor seems to surge @ around 3400rpm when cruising on the freeway...would that mean i should come up a couple of jets in the front?It has 1/2'' fuel lines and electric pump...also crane hi6 ignition.

russxr67

4.5 seems about right.
Pull the rear pv out ,plug it and jet up about 6-8 sizes.

xbgt74

The car is running better now with the 45 power valve and as mentioned plugging the back and putting 7 jet sizes in the back.After a few trial and error runs the jets in the front were changed to 73's and the car runs a lot smoother in the 2500 rpm range.Took it down the local motorplex and ran a 12.5@110mph....at 6200rpm with the timing set @ only 12 deg......reason being if you cranked the timing up it would ping badly.Probably due to the 12.6 :1 compression.I've tried the octane boosters...didn't make much difference so i'll try adding methanol to the fuel so i can crank it up to 30 deg. and rev it to 7000....hopefully it'll run low 12's or high 11's.

xdclevo

I would "hope" that had a tone left in it. With 408 cubes, 650 thou + custom cam and all, i would expect easy 10's out of it.
With 110mph, its showing mabey 440hp at the crank?

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10.70 @ 125.00 on the black fun top
408 Cube Cleveland.

xbgt74

Your probably right with the hp.......the problem being i have to back off due to pinging.....my mate who has been helping me with the motor rang up Dave of AFD and asked for some advise on why it would be pinging...he came back saying with that cam it could have a higher dynamic comp.ratio...to solve that i would have to retard the cam a couple of degrees.The car all up with me in it weighs over 3900lbs.Out of curiosity do you run methanol mix with 98 or are you running straight 98 fuel?I have got some methanol and will be putting in about 20%mix to see if i can wind the timing up to 28-30...see how we go with that.....i'll be happy to break into the 11's.....it's a street car no roll cage or full harness.

xdclevo

Mine has 11.7 comp and only runs BP98, and never had it ping.
Have tried 28/30/32 timing, but around the 28 it runs its best time/mph.

__________________
10.70 @ 125.00 on the black fun top
408 Cube Cleveland.

xbgt74

xd clevo just wondering what size headers and pipes you are running as we seem to think this could be causing a problem with mine as they are 4v tri-y?is your manifold a tfc?Tried some methanol today but still pings....

xdclevo

I have 2V headers which are only 1-3/4, but they are 4 into 1's. I used to run a single 3" but now have twin 3" with x-pipe. I have a 2V TFC which is the low version, and is Dave at AFD matchported it to my heads, and did the exhaust mods that are now on his latest heads, a D port. And also tiny 54cc chambers to get some compression into it. See pics.

__________________
10.70 @ 125.00 on the black fun top
408 Cube Cleveland.

xbgt74

Thanks for that.....the combo is working well for you.My heads are ported and the manifold is the low tfc 4v and is pretty much match ported but the interesting thing is the D shape exhaust which probably flow better coupled to the tuned length extractors.My twin exhausts are only 21/2''.Looks like i'll be aquiring some new headers and pipes.Do you still run with the 750 holley?

xdclevo

Yeah, a 750 Mighty demon carby with modified boosters and metering blocks.

__________________
10.70 @ 125.00 on the black fun top
408 Cube Cleveland.