Head flow for autocross

[SRD art]

My current SBC 406 has roughly 325 ponies and about 400 ft lbs. It runs a stock bottom end with 8.5:1 dished pistons, an XE268 cam, and self ported factory 400 "low performance" smogger heads. This motor is approaching the 100,000 mile mark and although it runs great I am after more power and a beefier bottom end.

I already have a fresh flat top pistoned short block 406 rebuilt and ready to go and was curious how my research compares to you all. The goal is approach 1 hp per cube and 500+ ft lbs to move my 3600 lb wagon around the autocross at a decent speed. I have been looking at bigger cams and budget head options and and like the Vortecs but rebuilding a junkyard set wouldn't save that much over a set of say Summit heads which are $700/pr.

The summit heads are 165 cc intake ports. Obviously small ports create velocity and = torque but 165 sounds really small. Most of my experience in the past has been drag racing and starting with a 200cc runner and porting from there. Those motors also launched at 4500, had a torque peak at 5000 and I shifted at 6500. I want to keep the power band low, like 2500-5500 and hopefully torque will be flat and peak around 3500-4000.

In your experience can a small 165cc port head handle the power goals I'm after?

Anybody know who mfgs Summit's heads? Thanks for insight!

[1BADBET]

I'm not sure what heads your looking at but if they're the iron small block heads they are probably dart iron SS reboxes. I just did a set of those and they went 260cfm @ .550 lift. Going in a budget street 350 Nova will make ~485hp. You can't just look at head flow though. There is a bunch of other factors, you do have more cubic inches than the heads I did do you could run a bigger head and make more power or just make the same at lower rpm. Other factors you would have to consider is gear ratio, vehical weight, cam specs (easier to spec a cam after you get heads rather than pick heads to match a cam) but cam specs also goes towards drivability and idle quality and they also plays a role in cylinder selection.

So yea short answer to your question is yes they will make 400hp (depending on cam and intake) and if they are the heads I'm thinking of they are reboxed dart SS heads. I could recommend cam specs but I'd need more info

[Ben@SpeedTech]

Here's that Summit head #- http://www.summitracing.com/parts/sum-152123/overview/

They have very small ports so that's what makes me wonder if they flow enough for a "big inch" 406. I found this old article, focuses on port size and is a pretty good make you go "Hmmmm" read. The end result seems big motors can still make crazy low end torque with big port heads...

http://www.superchevy.com/how-to/eng...formance-test/

Thanks for the input Jordan. I currently run a comp XE268 cam with 1.6 rockers. The car weighs 3550 without me, 3700 with me, and 38XX when I have a ride along. Currently it has 2.41 factory gears and 1800 stall converter. I'm switching to a 9" with 3.50 gears and a 2400 stall for the TH350. Cam is open, I was thinking maybe the XE284 but I'm not locked into anything yet. Right now the car runs high 13.90s at 98mph at sea level and goes through the lights at 4500 in 2nd gear so you can probably see getting off the line is the slow portion of the race.

With the new set up driveability isn't a question, my last build was an 11 sec daily driver with an old school big nasty solid cam and 4.56 gears. I miss driving that car every day but I don't miss the 6 mpg. With a high torque motor I could still get decent mileage even in this heavier car.

HP is a product of torque and when autocrossing you're rarely at hp peak so that really isn't a concern for me either. Mostly I want to make over 500 ft lbs below 4500 rpms, the rest will fall into place, whether it makes 350 hp or 500 hp, the torque is really what I'm after.

[72BBSwinger]

Depends on cam lift, then get as good as you can afford that flows the most just past your lift.

[1BADBET]

ive seen a sb2 headed 402 make 530 ft lbs at 4,000 rpm and make 850hp at 7200. So yea you can make tons of bottom end with big heads lol. I wouldn't reccomend those heads, they aren't the ones I thought by dart and they don't have a vortec style chamber like you would want. There's two different ways you could go depending on budget

Go with a set of profiler aluminum heads, they are the best bang for the buck aluminum head out there, take a bunch of weight of the nose of the car and make way more power. Kill some bottom end intentionally and put more gear in the car. The gear will accelerate the car faster and killing a little bottom end will make it easier to drive and roll into the throttle off a turn.

Option 2 is run the iron SS heads, I get them as a rebox for cheap and I can find out who else sells them as a generic head. Run the lower (numerically) gear and make tons of bottom, still a fun to drive fast car on a budget just not as fast as option 1.

Go roller cam if it's in the budget. The thumper series cam would be a good match since the ramps are designed very aggressive to make tons of power and not turn a bunch of rpm. They do make this series in roller and flat tappet. If you wanna do the aluminum heads I'd have s custom cam done, depending on budget of course and wether you went roller or flat they probably have s shelf cam that will get you close too.

As a basic guide for more bottom run smaller duration on a tighter lobe separation. For more power/ rpm more duration on a wider lobe separation. Cubic inch will also bring rpm down the bigger you go so take that into account also.

[Randy67]

400 sbc seem to want as much head flow as you can give them. Even 396 big blocks run pretty good with square port heads, which are on the big side. I am running a set of Victor Jr heads (215cc intake) on my 377 SBC (destroked 400) at autox and it does quite well, even with a cam on the big side. Sometimes I do wish I had built it as a 400, never hurts to have a bit more displacement

[mean buzzen half dozen]

Probably heads with at least 180 CC's & would need to flow about 280 CFM.

They will be restricting the bottom end from breathing well & will not rev too high of RPM, but should give you what you are looking for as far as HP & torque.

Anymore Q's talk to my friend Dave @ West coast cylinder heads. http://proheads.com/