452 cu. in. FE in 1968 Mustang

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pkm123
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Posts: 73
Joined: Sun Oct 30, 2011 11:54 am

452 cu. in. FE in 1968 Mustang

Post by pkm123 »

10SEC 68 is up and running again. This time with a MS3X sequential fuel and ITBs. Using alpha-N hybrid with a 36-1 wheel on crankshaft spacer, MSD distributer used as a cam sensor. The engine made 450 whp and 495 wheel lb.ft. at 5600 rpm on a dynojet, which is about 550 bhp and 611 lb.ft at the crank. The engine idles with a slight lope at 750 rpm, but will idle down to 600 rpm if I want it to. The cam is 248/254 at 0.05 or 288/294 adv. solid roller. I credit the mild manners to the ITB setup. The engine is 10.8:1 compression and runs on 93 octane without detonation.

Lessons Learned:

I added a 15K resistor to the crank sensor (+) lead to reduce the noise. Thank DIYautotune for that tip. Before that the engine would break up above 2000 rpm. Maybe they should add that resistor into the circuit on the board.

Had initial problems with the firmware. It was corrupted from the factory install (flooded the engine because 3 injectors drivers were always grounded. I will always reload the firmware when I buy a new megasquirt.

I have read a lot about sequential vs batch. The engine starts much better in sequential mode with one squirt instead of two. I think the 63 lb. injectors need more open time to get a good spray going. Idle injector pw is now 3.5 msec.

Be sure to set the injector dead time to a low number when using a larger injector (0.4) as the engine was could not to be tuned in "2 squirts". The fuel VE map numbers were below 0 with the deadtime set at 0.8 msec in alpha-N mode, two squirts.

I tried ITB mode, but the engine would not idle well. The vacuum at idle (750 rpm) was 10 in. and the vacuum at 1000 rpm was 15 in. This caused the idle to hunt in ITB mode. I switched to pure Alpha-n and is smoothed out. After I got a good Alpha-N map and then added the hybrid mode to help control the A/F ratios better below 1800 rpm. The engine map exceeds 90 mBar above 1800 rpm, about 5% TPS. I set up the fuel map with TPS bins at 0, 2, 5, 9, 15 etc. to increase the resolution down low, but needed hybrid mode to reduce the A/F ratio fluctuation.

The engine only runs in the lower left 20 or 30 bins and the 100% bins. The rest are transitional and aren't really used. If I was to do this setup again, I would use a progressive throttle linkage to reduce the throttle sensitivity and add more TPS bins below 9%.

I'd be happy to help others with advice if they are using ITBs

Thanks everyone
pkm123
Helpful MS/Extra'er
Posts: 73
Joined: Sun Oct 30, 2011 11:54 am

Re: 452 cu. in. FE in 1968 Mustang

Post by pkm123 »

Dyno sheet
Matt Cramer
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Re: 452 cu. in. FE in 1968 Mustang

Post by Matt Cramer »

Nice work!
Matt Cramer -1966 Dodge Dart slant six running on MS3X
pkm123
Helpful MS/Extra'er
Posts: 73
Joined: Sun Oct 30, 2011 11:54 am

Re: 452 cu. in. FE in 1968 Mustang

Post by pkm123 »

Just thought I'd add an update.

I changed the fuel map to include a lot more bins below TPS of 14%. Then I interpolated these bins. This gave me a ballpark tune to work with. Using VE Analyzer, I then drove the car and re-tuned. This greatly improved the AFR variance. The AFR's now stay between 14 and 15 everywhere in cruise. I also followed the recommendation from the MegaMeet. I graphed MAP x RPM vs. PW (or Duty cycle) and the scatter plot is much tighter than before.

The throttle bodies are 50 mm. The engine makes 550 hp, or 69 hp/cylinder. According to the Jenvey website the throttle bodies are on the upper end of the recommended size for this horsepower. They would recommend 48 mm. This would allow easier tuning, but it may affect max hp.

I am pleased with the outcome. I would recommend the AN-hybrid approach over the ITB tune for engines with a large cam and low idle vacuum.
Has anyone have more insight into this application?
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