3400 with 260whp

[EspanolaGuitarista]

Before I had my computer stolen...

...I did a full work-up on the 3400. I got everything nearly identical to the 3400 specs. A 206/206@.050 cam will work great. Don't bother porting the heads, they need flow not volume. Porting in my opinion won't change those numbers enough to make a difference. Make some shorty headers with 1.5 inch primaries inside diameter. a suggested length is 31 inches and does make a noticeable difference in simulation, but that isn't practical. Some think larger primaries make more power, but when you go from a small port to larger primary the gas expands and slows down. I would think square tubing to cover the D shaped port would be the best but that may also be impractical. 65 mm throttle body and blocking off the heat crossover got me about 225 horspower in the sim. That's a good 40 hp over stock.

[Mars]

im sure no 1a runnin 3.4 dohc cam in a j or l body that i ve seen or heard bout

I've seen one in a third gen J. It's a nice looking show car, with some wild paint yellow, to red-purple, blue colour changing kinda paint if I remember correrctly...., everything on the engine is polished.

I can't find the pics now, but they are someplace. Doubt it was ever raced or anything.

[SappySE107]

Porting the 3400 heads for more flow without making a lot more volume is not only possible, but also makes quite a difference in simulations. Exhaust primaries are sized based on power output, not the size of the ports. 1.5" is too small for anything more than a mild build up 3400.

[EspanolaGuitarista]

Well...

....I understand your point of view Sappy, but you can't change the rate of flow without changing the port volume. Now that I recall changing the rate of flow at mid to high valve lift does make a difference, because of valve shrouding .25 of total diameter. The intake to exhaust ratio was biased about 78 percent or so. Getting that number down required me to run 2 degrees less duration on the exhuast side. So it was actaully 206/204 or 206/206 with .05 less lift on the exhuast for good balance. That may not work in the real world though. I was thinking 206/206 for the sake of an easy grind that would lower the ratio slightly. The larger the duration the more the ratio seems to come down. Anyways, if your thinking aboout running more than 206 degrees or 260 cam, you need more compression or your just wasting your time, in my opinion. You also need the 65 mm TB. The older TB won't cut it.

[SappySE107]

I disagree on both of your statements. Increasing velocity is possible (and is what I do) from porting. Yes, I remove about 1.5cc from the intake port, but the flow increase means higher velocity in the areas I didn't touch. You can shape a port to streamline the path of flow and the motor will see a smaller port. On 3400 heads, i increase flow substantially from the combustion chamber work. That changes the rate of flow without changing the port volume.

You don't need more compression to see gains from more cam than 206/260 duration. You have to advance it to keep your bottom end happy but if you want more mid/top end at the cost of bottom end, you can keep your 9-9.6:1 compression.