Hi,

This summer I am thinking of filling the exhaust crossovers, and then came up thinking what would the next step be gaining hp (whilst the engine out of the car, again..).

The car is a 1970 Delta 88 being used for cruising around and doing great burnouts once in a while

Current specs:

Std bore 455, new pistons, 9.9:1 compression (measured)
Mildly (home)ported G-heads
Full length headers 1 3/4 to 2.5 inch dual exhaust
Quadrajet 750, now a little bit on the lean side at cruise
Edelbrock perfomer intake
Hydraulic cam .496/.512 lift, 226/230 dur @ .050, 110 Lobe sep
1:1.6 roller tip rockers
HEI ignition
2.93:1 gears

So, what do you guys (and girls?) think. Do you think this engine-combo line up or are there a obvious "next step"gaining hp.
I would guess heads, or cam?!

Best regards,
Fred

 

The question is what are you going to do with your HP gain. The 2.93 gears are a stumbling block.

 

Hi,
Thanks for replying! Sorry I didn't write that. It is only meant for street use. I'm not very familiar with english, what do you mean with "a stumbling block".

 

"Stumbling block" means a problem. Your rear axle ratio is great for mileage or high speed runs at Bonneville but not so great for performance on the street. You'll put a lot of effort and money into the engine but the rear axle will limit the results. Unfortunately, different gears for your car's rear axle are very difficult to find. That axle is not supported at all in the aftermarket.

As for filling the crossover, why? You'll never see the difference for "cruising around", and cold starts will be worse. This is another case of mimicking what drag racers do without understanding why. Filling the crossovers makes sense if you are looking for the last few hundredths of a second on the track AND if you rejet the carb to take advantage of the cooler inlet mixture. On the street you'll never see or feel the difference, other than the rough running until the engine warms up.

 

Hmm joe I have to disagree a bit.
While i agree filling the crossovers won't affect his "cruising" performance, filling the crossovers and welding the center divider is free Hp when using headers. It will most certainly improve scavenging on those middle four cylinders. However only he can decide whether or not that would be worth it.

Freu, does it have an exhaust crossover or H pipe? If not that will improve low rpm performance as well.

 

I'm not a drag racer or an engine builder with a lot of experience, but I would guess that fine tuning the carburetor and ignition system would help maximize power. Perhaps use an oxygen sensor and air/fuel ratio gauge to tune the carburetor to ensure you are getting the most out of it that you can.

You did not say if your G heads had larger valves, so if not, this would be a good upgrade.

 

Thanks for sharing your knowledge!
I haven't thought much of that rear end but what you (Joe) say totally makes sense. Maybe I should rethink filling those crossovers after all. I have a electric choke though.
And to you cutlassefi, I don't have a H-exhaust crossover, might consider that!
Drag71, I do have air/fuel-ratio sensors welded to the header collectors so that will help the carburator adjustment. Unfortunatelly I don't have the bigger valves.
Interesting thoughts, thanks again!
Do you think a different kind of camshaft will line up better with this build, still for my purposes (street use with enough vacuum).

 

Mark,

I don't disagree with you in general, but the OP's car is a 1970 D88. It's a heavy street cruiser. You can't get headers and if you even want duals you're stuck with the crappy, convoluted driver's side manifold to clear the steering box and shift linkage. In the grand scheme of where the OP needs to spend money to get the most bang for the buck, filling the crossovers wouldn't be high on my list for this particular car. Frankly, as I noted, I'd spend my time and money on a better set of rear gears. As you know, performance requires a "systems" approach, not just focusing on the engine.

 

In his original post he stated he has headers. You have a decent engine now. If your get the rear end setup with a more performance oriented gear ratio you and your engine will be much happier. A cam change will not help you until you accomplish this.

 

DOH! I missed that completely. I'd be very interested in finding out what brand/part number they are.

 

That is a very valid question!
Bought one of the cheapest hooker headers "for 1970 Delta 88" knowing I had to do a lot of cutting and welding, especially on the drivers side. Ended up having to cut and reweld every pipe on the drivers side and two on the passengers side. It was challenging though fun and ended up pretty good.
WP_20131022_006.jpg
Note the header lying to the right where the pipe from cylinder no 3 had to be bent upwards to fit. Quite funny imo.
After reading your thoughts and opinions I feel confident leaving the engine alone for a while and maybe start to look for an other rear end. Thanks once again!

 

Nice work on the headers. Let us know how you make out, keep in mind the cam you may want to run and the gearing to match the power curve. Cutlassefi (Mark) is a good go to guy for that kind of help.