[vertbird]

I'm trying to get a little more out of this block and head combo, specifically 350-400hp. Right now I'm at about 275hp based on 1/8th time and perf. trends software. The 6x-8 heads have been milled, cam is 210/221/112, dist. curved and a Cliff qjet. Long branch manifolds and 2.5 mandrel exhaust out back.

This is about 80-90% street, with some 1/8th mile runs. The car is pretty clean and I'm trying to keep it's appearance orig. and keep the 6x heads.

I know CR is hurting so I'm thinking of zero decking block, possibly a cometic thinner gasket, 5cc dished pistons instead of the current 15cc and a hyd roller in the 216/226 range.

Any other thoughts of trying to get 350 street hp out of this block/ head combo?

[steve25]

Airflow will provide you with more performance than the additional compression you will be able to run on pump gas.
If your heads do not have 1.77" exh valves, than its time to get them changed over, while at the same time you have the full exh side ported, and the intakes bowl ported.
This rework when done right should get you 235 cfm@28" h2o on the intake side, up from the stock 205 cfm and this should be enough to get you to 375 HP, but you will need a cam of close to .500" lift. A cam of .450" lift may not make it to that HP number.

[dmac]

Instead of changing cam, you could change rockers to a higher ratio. As long as you stay under about .480 lift, you could keep everything else the same. It is just an easy first step that involves very little wrenching. But even if you remove the heads, changing cams is another big step. More lift with some 1.70 rockers and better breathing by doing port/valve work and bumping compression to 11:1 if you can get the gas will probably get you what you want.

But that said, a cam, and carb with heads set up for higher lift, even without porting is the "right" way to go about it. You start needing the porting at higher rpms, but that kind of machine work is the biggest expense. Done right, it is a one time expense that will serve you well if you ever want to take it further.

What I found, is that I would have been better off in the long run by buying some aftermarket aluminum heads, then you can even run a little more compression too. By the time you change valves, guides, port,springs, retainers, and any other machine work, you are getting close to a set of basicaluminum heads.

The best way to put it is- it all depends on how much you are willing to spend.

[vertbird]

Don't the heads have to be modified to clear the pushrods if I go to 1.65/1.7 rockers?

[Cliff R]

Your plans are sound, and will improve power at every rpm. The stumbling block are the 6X-8 heads. Even cutting them pretty hard they are still over 90cc in the chambers, and barely get a 400 to 8.5 to 1 with a flat top piston and zero deck height.

LOW compression 400 engines just don't make killer torque at low rpm's, which is what is required to move around 2 ton cars effectively with moderate gearing and converter stall speeds......Cliff