Hey guys,

This is my first post here so bear with me.
I am sure that you've all heard these questions before but I cant seem to find a similar topic when I search the site so I am going to come right out and ask these questions.

Okay I have puchased a set of cast Aussie heads (60CC) assembled and was wondering a few things about what to use with them. Keep in mind that I want the daily driver on this one but would like lots of power also .

1. I know that this is going to boost my compression 1 to 1.5 points overall so can i use the stock piston with this head or is that a bad idea?

2. Do I have enough valve clearance to when I use the stock pistons? Lift under .510.

3. A chevy man that knows a little about engine building told me that i should get a much larger cam than stock with a long duration to bleed off some of that compression for use with pump gas. Is this a good idea? I was thinking of using the comp cams 268h for this. If i can use a different cam which would you suggest?

4. If i have the heads machined for roller rockers do i need high rise valve covers for rocker arm clearance if the valve lift is under .510?

5. Last one. If anyone out there has a 78 or 79 bronco that has air, do you know if the high rise valve covers will fit under that darn air conditioning fan box?

I love both positive and negative feedback so let me have it.

thanks

 

Welcome to FTE

You're building virtually a carbon copy of the motor Tim Meyer built. He documented it well on his website. Here's the link:

400 Ford

 

Please don't listen to a Chevy guy when building these engines. It's nothing personal, but my best friend is a Chevy guy, and he doesn't understand the differences. Trust me, there are many. You will find that there are some very knowledgable people here, but it takes a little time to figure out who they are. Long duration cams can be the devil, if you are looking for good low-end torque. You may want to check some of the cam threads in this section for some good advice. Alot depends on what you have and what you want it to do. Keep us posted and good luck. I will be using the Comp Cams XE-262 for that exact reason, but it's not a daily driver. I feel the 268 duration is a bit much for a heavy truck, but the lift and the ramp speeds of the XE cams will work to create low-end torque better than an H-series cam, but should still have great mid-range and decent top-end through 5200 RPM's. Somebody please correct me if I'm wrong.

 

I used the comp cam extrem 4x4 265 DEH, works real good. This was 10 years ago. The first one was the 275DEH was alittle to big for what I wanted, but drove it for 2years. I didn't have the fancy heads, So I shaved mine and becked my block. The stock valve covers will cover the roller rockers. I'm running them on mine. I had my heads worked on to run the rollers, worked out real good. And yes the taller valve covers will go under the a/c box.

 

That's what I meant by the comment about long duration cams. Unless you are using your truck as a racer, you will lose tons of low-end torque if you have too much. These trucks are way heavier than the average muscle car.

 

Its hard to race a 6000lbs, Tools and all.

 

I pretty much built the same motor that you are contemplating, three years ago. If you go with the stock pistons, sitting almost .060 down the hole, you will lose the effect of the quench of the Australian heads, result: detonation. If you deck the block to eliminate the excess deck height, you get too much compression, (in my case, 10.8:1) result: detonation. I couldn't even get it to run on 104 octane gas, and I tried just about everything. I suggest that you try to get some of those pistons that Tim Meyer has that have the higher deck height built in and a (32cc?) dish already milled in. That should give you the lower compression that you need, (around 9:1) and still keep the quench effect that the closed chamber aussie head provides. You might get a bunch of posting geniuses that claim to be running 10:1 or higher compression ratios on pump gas, but I wouldn't believe them if I were you.
By the way, I was running the aussie heads, KB pistons KB148 with a 13 cc cup, engine block decked to only .015 deck height, a comp cam 275 DEH (.515 in .541 exhaust lift) harland sharp roller rockers) they do clear the stock valve covers with baffles intact. also, stock exhaust manifolds, edlebrock intake, 750 CFM vacuum secondary holley. This was in a 1977 Thunderbird with a C-6 and a 3.00:1 rear-end. It would run and idle great, but if you stepped on the gas it would detonate bad.
I'm in the process of redoing that engine right now, only I'm using stock pistons, stock 2-V heads, and with the deck height eliminated, I'm hoping for 8.95:1 compression. We'll see if that eliminates the detonation.

 

9.3 you have to run 91 octane or it will detonat. I'm runing at .006 in the cy. with .072 off the heads.