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Boss Nine flow w/ larger valve

5K views 5 replies 4 participants last post by  c.evans 
#1 ·
I was wondering if anyone had any information or flow numbers on a larger intake valve (2.400-2.450) and the appropriate porting, or if its even possible. Wanting to build a new engine, and the class rules are fairly liberal, except must be a stock style head, and an iron block, and the Boss definitely fits the bill, plus the cool factor is there.
Looking for as much torque as I can get, as the truck is going to be around 3800 lbs or so, and run in both fast track and some shallower bog conditions.

Looking toward.
LSM lightened Eliminator, 4.700 bore
4.3 or 4.5 inch stroke
14:1
Single carb-SV1?

Just looking to see if it's possible to get to or past the 1100 HP mark.

Thanks
 
#2 · (Edited)
Just my own experiance with Boss engines, even the Nascar version of the Boss 429 had 2.400 intakes. At that time they ran the ovals at about 7000 rpm. All of my Boss engines used 2.400 intakes, some had 2.00 exhaust. There is a problem with too much valve size when a lot of cam overlap exceeds a certain point. Because of the chamber shape and valve angles it is possible to have the valves interfere with each other.

1100+ hp should be no problem with the size engine your thinking about,
 
#3 ·
If i was going to build a big $ BBF hemi for any kind of class racing i would get it in writting that the heads would be legal, you go showing up with a 1100+hp BBF with "factory" style heads and the chevy boys will have your motor banned in seconds. I don't run class racing but i do hear about this kind of thing happing to the BBF guys all the time. :(
 
#4 ·
I've had a couple of sets of Jon's Boss Nine heads in here to port and flow. They are certainly nice heads. They come with a 2.300" intake valve and while I believe a 2.350" can go in with no problem, I also believe you'll have to be removing the seats and replacing them with bigger o.d. seats in order to run the 2.400" intake valve. So it will be a lot of extra work.

Claude at CHE has a rule of thumb guideline the the o.d. of the seat needs to be +.100" larger than the o.d. of the valve. Now then that's his suggestion, but many of us head porters are violating that rule all the time and pushing the limit. I've had seats be no bigger than +.050" of the valve head diameter on the intakes. The problem with getting seats too thin, is that we lose structural integrity and the seat won't be able to maintain it's press fit.
 
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