He351cw

Has anyone seen an MPG gain from porting the exhaust housing on a 351? What about larger turbines? Any effect?


Love the way my 79 runs with it but daily driving mostly hwy id like to see better than 16 mpg. Been trying to stay under the boost and havent seen much change. Cruising egt is 750-800 and wraps out the 1600* pyro fairly easily

For cruising, exhaust flow is better than boost pressure.
Best average mileage I ever got consistently, not towing, was 23mpg, in a 91.5 with the stock h1c turbo.

Mark.

Mark Nixon said:

For cruising, exhaust flow is better than boost pressure.
Best average mileage I ever got consistently, not towing, was 23mpg, in a 91.5 with the stock h1c turbo.

Mark.

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Thanks Mark, thats what i was trying to say, been keeping out of boost on hwy.

I see you're running a 518 auto.
I think 16 is good for an auto that's lugging the engine, like those do in overdrive.

Mark.

Mark Nixon said:

I see you're running a 518 auto.
I think 16 is good for an auto that's lugging the engine, like those do in overdrive.

Mark.

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Thought it would do better with the recent converter upgrade.

Ill go ahead and give specs

Tcs 89% converter
3:54 gears
33” bfg ats
5700 lbs roughly
6x13 sac
Timing skipped one tooth and turned just past stock
Mild porting

My towing experience tells me it's just as economical to spin the engine just a bit harder, than to lug it and make it work at lower rpms.

A shining example of this is when I swapped from a 47re to a 5 speed in a 96, I gained 5mpg and, IIRC, it increased 500 rpms in overdrive at road speed, in 5th.

It made a night and day difference in how the truck performed overall.

In truth, I believe the internal gear ratios for automatics are NOT favorable for these engines, they either are spinning too fast, or lugging the engine.
Deeper gears in the axles seem to help this, on autos.

The biggest culprit is the final overdrive ratio.

Mark.

Thanks Mark. I hear what you’re saying.

Although i dont feel as if im lugging the engine, at 65-70 it feels happy - just under boost, doesnt seem to be working hardly at all, but the turbo is quick to light off, can almost feel as if the exhaust is too tight


If i could squeeze 1mpg and drop egts a bit in the process by opening the ex housing up id be happy wih that.