Four speed street cruiser

[red79]

Been away from the forums for a while as job and living situation precluded virtually all progress on what was once a quite optimistic build schedule for my 72... looking back at posts I made in 2010/11 are a good way to remind myself to be humble in the face of gods and destiny haha.

But, now that I'm moving to a house with a proper shop, I'll be able to finally get all my tools in one place and gut the Charger for driveline, electrical, and body overhaul that I've been looking forward to since I brought her home.

To that end, I've started to reevaluate the parts I have been accumulating over time in the face of new goals and developments in the aftermarket. I had originally planned on building a well-mannered powerplant that would pull hard down low in street conditions (1500-4000 rpm) and refreshing the 727 currently mated to the worn out 400 currently in the car. But now that I'll have the time and facilities to do a proper teardown, I won't be able to justify leaving out a third pedal and doing an 833 conversion.

After that long-winded preamble, my question is: given my parts list below, will I end up with a well matched combo that behaves as well in front of an 833 as it would in front of a torque converter, and will it run on 91 octane?

440 motorhome block (1973), +0.030"
Steel crank, set up for pilot bushing
Reconditioned stock rods (ARP hardware)
Speed pro 2355 pistons, zero decked, assembly balanced
Engle k56h hydraulic flat tappet, 224@0.050", 0.510" lift w/ 1.5 rockers, 110deg LSA
Performer RPM intake
Holley 750 DP
1 3/4" or 1 7/8" primary headers
0.039" compressed head gaskets

With my stock 902 open chamber iron heads, assuming a 92cc chamber volume, the static CR is just over 9.4:1, and the dynamic CR is 8.67:1 8.0:1 at sea level. [earlier math error corrected]

If budget allows, I'd like to get a pair of sidewinder heads, which would give a static CR of 10.1:1 and dynamic CR of 9.288.6:1. [earlier math error corrected]

I'm hoping to mate this to a trans and rear end for a low final drive ratio. One option is a standard steel case 833 with the current 2.71 8-1/4" rear, should provide mild manners and great highway rpm until the rear breaks, while saving up to swap in a passon OD conversion gear set and 3.55 8-3/4".

A similar alternative is to use a late 833OD with the IBR turned down to fit a standard big block bell housing, and swap rear gears to 3.55. Should live long enough tooling around town and on the interstate that I'll have time to save up for a beefier rear axle assembly, and if I break the aluminum 833OD case can always buy a few more complete for what a passon OD costs.

So, does this sounds like a feasible setup, headache and detonation free in town winding 1500-3500rpm and turning lazy revs at 65 mph?

[heyoldguy]

No, it doesn't sound detonation free.

[c00nhunterjoe]

I would say it is possible, but will be difficult and the conservative advance curve needed to achieve it lugging a 2.76 rear at 1500 rpm will make the car feel lazy.

[red79]

Hmm, that's pretty much what I've been worried about... I picked a shorter duration, high cylinder pressure cam specifically to make torque around 2k rpm, but will it make any overdrive-cruising combo undriveable?

Should I abandon the thought of 1800 rpm @ 65 mph with a grind like this, and stick with a standard 833 + 3.23 rear gear?

[red79]

Been ruminating on this a bit more, how about --

A) Standard 833 with a 3.23 rear gear, with 28" tires that means cruising at 2500 rpm at 65 mph.

OR

B) Late 833OD gearset in an iron case (avoid the countershaft problems of the aluminum case ODs), and a 3.55 rear. The granny 1st in an OD would take off from the line like 4.10s with a standard 833, 2nd would be similar to the aforementioned 833/3.23, 3rd is direct drive, and OD would keep a low 2000rpm on the highway. With street tires and staying off the track, I wouldn't worry about the tranny surviving.

Similar builds to this make torque approaching 400 ft-lb by 2k rpm... is there no good way to take advantage of it without worrying about detonation?

[firefighter3931]

A 10:1 aluminum headed 440 with tight quench should be able to run fine with a 224@.050 cam unless it's excessively advanced. The 9.28 dynamic is high and I'm guessing there's a mistake in the math somewhere. 


Ron

[red79]

Thanks for the vote of confidence Ron. I went back and tried a few different dynamic CR calculators, looks like the one at wallace racing that I had used wanted the 'true' intake valve closing point, not the point @0.50" from my cam card. I'll note and modify my original post.

Looks like my numbers are DCR 8.0 for the iron heads, and DCR 8.6 for the aluminum. Much more comfortable! I'm definitely relieved.

Detonation fears dispelled, the secondary question remains: will there be enough low end grunt to make a highway gearing enjoyable? Or would I have to make sure I don't drop below 2k rpm on the upshifts?

[firefighter3931]

It will have plenty of low end grunt. I wouldn't hesitate to run that combo.   

Now I wouldn't lug the engine at 1500 in 4th gear either but keeping it in the 2000 rpm range should work fine. 

From my experience the closed chamber aluminum head builds make best power at 34-35* total timing. Adding additional timing had the hp power numbers going backwards (on the dyno) so the key is to keep total timing in check to make best power and ward off detonation. Attention to detail with regards to the timing curve is important. 


Ron

[red79]

I suppose the key will to have a short mechanical advance that comes in very early, all in by 1500-1800, on a base timing of around 18*. Someone around here told me that the a firecore RTR would be fine for these power levels, clean up the engine bay, and has an advance curve that's easy to tweak without welding slots

The hard part in my opinion will be dialing in the vacuum advance for low rpm cruising, maybe another 15* or so when the throttle is just barely cracked, but pulling it quickly when load increases. I suppose it all comes down to what kind of vacuum signal the carb port is generating, and the setup will be much easier to get sorted out once the engine is actually built 

[firefighter3931]

With a combo like that 16-18* at idle and 35* total all in by 2500 seems to work very well. 

My buddy Denis has a similar build ; 440, Stealth heads, Crower 222@.050 cam, CH4B dual plane intake, 750 carb and HP exhaust manifolds. We have his RTR distributor set up with 16* at idle and 35* total. It runs like a champ ; boils the tires at will, pulls 16" of vacuum for power brakes and gets 15mpg on the hwy with 3.55 gearing at a steady 60 mph. He's even run it on midgrade fuel with zero detonation. 

The RTR is definitely a top shelf piece and it's ease of adjustment is a joy to work with. Lots of guys are running them with great success. I have some out there on big stroker street hemi builds making 650hp 

Get to work and build that thing ! 



Ron

[red79]

Get to work and build that thing ! 

Cheers to that!