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Hello, I’ve followed this forum for awhile now but haven’t posted much and I’d like to ask for some help in interpreting the results of my first attempt at dyno tuning last weekend. A friend of a friend owns a 224x dynojet. His specialty is computer controlled turbo engines, not vintage carbureted engines so I did all the tuning adjustments myself. Cool b/c it’s interesting and I’d like to learn as much as I can but my knowledge base is limited and my experience base is pretty much zero. The basics on the car are as follows. It’s a 66 mustang with a 302 that I’ve owned since ’86, first car at age 16. Up through ’94 I did a decent bit of work on it, either on my own or with help from my father, including paint (twice, 1st attempt was a wimbeldon white two-tone), suspension, a T-5, as well as the engine. After that life intervened and the car ended up sitting, inside, from 1998 to 2010, when I got it running again. The engine has about 6500 miles on it and the details, to the best of my recollection are:

-68 302 block, bored 0.020” over with ARP main studs
-Stock crack and rods with ARP rod bolts

-Early 289 hipo heads with 1.94” intake and 1.60” (I think) exhaust valves installed by a local shop. I ported the intake and exhaust ports myself, no ideal how well I did but I took a lot of metal out.

-Cast pistons with larger than stock dishes (I hadn’t planned on that but kept them). I think the compression is on the low side, with the larger dishes and smaller chambers, maybe in the ballpark of a stock 68 302? Last year I checked cranking compression and got: (cyl 1)-159 psi, (2)-154, (3)-157, (4)-157, (5)-158, (6)-158, (7)-159, (8)-152

-generic Shelby-style Tri-y headers

-Camshaft: Erson HiFlow 1H, hydraulic flat tappet, .504” lift, 296 adv duration, 228 duration at 0.050”, 108 lobe separation angle
-Pertronix billet distributer with ignitor III module and flamethrower III coil
-Edelbrock Performer RPM intake (not ported)
-Edelbrock 600cfm Performer Carb.

I ran the car once on the dyno in 2010 without trying to do any tuning. In 2011, I had the exhaust changed from a dual 2-1/4” inch system with generic turbo mufflers to a system with 3”pipes from the collectors to 3” dynomax superturbos to 2-1/2 inch tail pipes. The results of the dyno runs are below with the peak hp and torque listed in case I didn't upload the curves correctly.

Runs 2 and 3 compare the old and new exhaust.
Old: 213 hp, 240 ft-lb, New: 238 hp, 267 ft-lb

Runs 3,4, and 5, compare carburetor adjustments
following the procedure in the Edelbrock manual.
Run 3 was the stock settings. 238 hp, 267 ft-lb
Run 4 was 2 steps rich (8%) on the primaries only. Slight decrease 236 hp, 263 ft-lb

Run 5 was 1 step lean (4% from stock), for both primaries and secondaries. 240 hp, 270 ft-lb

Runs 5,6,7 compare timing adjustments
Run 5 was 8 degrees initial, 32 total. 240 hp, 270 ft-lb
Run 6 was 17 degrees initial, 41 total, 239 hp, 266 ft-lb
Run 7 was 12 degrees initial, 36 total, 236 hp, 267 ft-lb

Basically, the exhaust gave about a 25 hp gain, but all the other adjustments didn’t really change anything. There was about a 2% spread in peak horsepower among the tuning runs. Peak hp came at about 5000 rpm then the curve was pretty flat until a sharp drop between 5700 and 5800 rpm, which I have no explanation for. The results have me a bit confused as I had expected to see some effects from the tuning changes. As far as specific questions go, I’d appreciate some help on:

(1)-should I have continued to richen the carb and would that be expected to increase power? I see that air/fuel curves for Runs 3 and 4 are pretty close between 5000 and 6000 rpm so richening the primaries only didn’t seem to change anything in that range.

(2)-My understanding is that the cam should peak closer to 6000 rpm, rather than the 5000 I’m seeing. Does this seem correct and, if so, is it possible I have another limitation that is suppressing engine performance and the effects of my tuning attempts?

(3) From reading posts about somewhat similar engines I get the impression that my carb choice may not have been the best match for the rest of the engine. I’ve seen a lot of 650cfm holleys, esp. double pumpers, as well as some 750s, mentioned. Would a carb change make sense?

Sorry for the long post. Thanks in advance for any comments.


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