Thread: 406 sbc combo-need help!

Tweet

I have a 400 sbc bored .030 with flattop pistons (2 valve relief) and I am using 5.7 rods with a stock crank. My cam is a comp cams solid lifter 288/292 duration .550/.560 lift 106 lobe centers with 1.5 full roller rockers. The heads are #461 casting 2.05 intake 1.6 exhaust valves. My intake is a weiand team G single plane with a 800 holley DP carb. HEI dist with MSD coil. The trans. is a turbo 350 with a 3200 stall and the rearend is a 8.5 ten bolt 4.56 gears. The car is a 1971 nova that weighs 3100lbs with me in it. I recently took this car to the strip and with slicks went 12.80 at 101mph at Heartland Park in Topeka Kansas. What am I doing wrong?

Seems head limited. The combo looks strong except for small converter and heads. Other than that, it's very close to my 383cid combo in my Luv that runs 10.80's on pump gas.

Does it feel like it's laying down on you above 5K rpms? Seems like it should run better than that even with the humps.

Try a better intake and a bigger stall speed . Also what tube size are your headers ? And are those fuelly heads ported ? I like fuelly heads but on a SB 406 you need some heads like world sportsman II 200cc intake runners . But I do really like your build .

What rpm are you shifting at? And what rpm does it start to drop off power? Camel Hump heads if they aren't ported will only let a 406 make power to about 5000rpm or less. Your cam is designed to make power up to 6500rpm. It takes a VERY expensive/good portjob to make camel humps support that RPM. Like the others I would suggest getting an aftermarket set of heads around 200cc intake runner.

Another question is who ever did the heads... Did they deshroud the valves when they installed the 2.05's? The combustion chamber is real small on the 461's and will not flow well unless that is done. They will actually flow less than 1.94 1.5's if it is not done.

Originally Posted by 69elko

Another question is who ever did the heads... Did they deshroud the valves when they installed the 2.05's? The combustion chamber is real small on the 461's and will not flow well unless that is done. They will actually flow less than 1.94 1.5's if it is not done.

This is very true . Fuelly heads are great for a street strip mild 327/ 350 But when your talking over 355ci or over 400HP . Run something better . And they do flow better with the 1.94 1.50 when stock unshroud . I have two sets of #186 fuellys with the bolt holes in the fronts 1.94/1.50 . Great budget 350 heads when under 400HP !

It appears the mph is very low for the et which is telling me your gear isn't matched to your revs.

You must be nosing over on top? What rpm do you shift and what rpm at the traps?

Two ways to skin the cat:
-get the motor to rev higher (per suggestions above, i.e. better flowing heads, intake, etc)
-use a taller gear (numerically lower) to make better use of the torque down low...

Sounds like the cam is a high winder so either use a shorter cam and shorter gears or better heads

Two cents...

-Chris

Originally Posted by ghostchaser6t9

I have a 400 sbc bored .030 with flattop pistons (2 valve relief) and I am using 5.7 rods with a stock crank. My cam is a comp cams solid lifter 288/292 duration .550/.560 lift 106 lobe centers with 1.5 full roller rockers. The heads are #461 casting 2.05 intake 1.6 exhaust valves. My intake is a weiand team G single plane with a 800 holley DP carb. HEI dist with MSD coil. The trans. is a turbo 350 with a 3200 stall and the rearend is a 8.5 ten bolt 4.56 gears. The car is a 1971 nova that weighs 3100lbs with me in it. I recently took this car to the strip and with slicks went 12.80 at 101mph at Heartland Park in Topeka Kansas. What am I doing wrong?

Like everyone has said the heads are a little small.
I would also like to see a min. of 12.5 to 1 for a comp. ratio.
If this is a true drag car then I would run a 4,500 to 5,000 stall speed.
What are your 60 ft times?

.................... some people just dont get it

..............Get what????

My 60ft time was a 1.81 and I was shifting at 6500 rpm. I went thru the traps at 6500 rpm. The heads have not been ported and the valves have not been unshrouded. First and second gear felt like the car was pulling hard but when I shifted into high gear, the car nosed over past 5000 rpm.

With those heads I'm surprised you got it to wind up in 2nd. The nosing over is the heads. Terry Rosebush on Ebay is selling the old style Dart heads for 399.00 a pair bare. They are a good buy. I got a set for a friend, put a good valve job in them and swapped all his stuff over. That along with an intake swap picked him up a second in the quarter. A 200cc head will be good on there and if you think you might ever want to go faster, 215cc would be better.

If it pulled hard in 1st and 2nd all the way to 6500 and then nosed over in 3rd I wonder if you may have a fuel delivery problem. What sort of fuel pump do you have? And what size fuel line are you running from the tank? Also if you are turning 6500 at only 101 mph you are either running a very short tire, or the converter is slipping. With a similar set up in a 63 Nova, with 5.13 gears and a 28 inch tire I was running through the traps at 110-111 mph turning 6500.

Pat

Originally Posted by ghostchaser6t9

My 60ft time was a 1.81 and I was shifting at 6500 rpm. I went thru the traps at 6500 rpm. The heads have not been ported and the valves have not been unshrouded. First and second gear felt like the car was pulling hard but when I shifted into high gear, the car nosed over past 5000 rpm.

Those valves could definately be causing the problem. Even with 1.94's the 62cc chambers don't leave much room for flow. If they are a decent set of heads I'd take em off and save them for a 327 or 350 build. Unless you are willing to spend a lot of money on them. It's possible to get the heads to flow 250cfm which is about what you need to rev the engine to 6000rpm. Take a very good head porter and lots of dough. You could see 230cfm with a pocket port job and chamber deshroud.

Your's very similar to my old 406. The biggest differance being the heads, I had Canfield 197's and a small solid cam, and 373 gears. I ran 12.20's in a 72 Monte Carlo 3800lbs. My recommendation would be to maximize the torque, there is only so many 6500rpm run's in a stock bottom end.

'76 2 bolt block .30 over studded main's
stock crank turned 10-10
5.7 rod's resized
cast flat top's (less weight)
Lunati 501-508 lift solid cam
Canfield Aluminum heads 2.05 valves
1.6 intake 1.5 exhaust both crane gold
Performer RPM intake w/ 750 vac. sec out of the box
MSD dist, 6al box
t-350 w/TCI street fighter converter foot braked to 2500rpm
12 bolt with 3:73's
BFG drag radials

Best 60' 1.69

Ron