454 Efficiency - Compression vs port velocity

General engine tech -- Drag Racing to Circle Track

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Re: 454 Efficiency - Compression vs port velocity

Post by burbfixer » Fri Nov 10, 2017 12:10 pm

Yes, I've been keeping my eyes open for an inexpensive set locally. The chamber size would only get me part way to my cr goal, but it seems they would be better than what I have for several other reasons as well. It's not that I'm stuck on the pp heads just because they're the smallest of the small, it's just that they are what I already own. I'm curious if you've tried l29 heads in a combo yourself and what you experienced? I've driven stock l29 trucks, and they are definitely a big improvement over the l19.
The 'driving experience' comments you've mentioned with those combos are very helpful.
I may consider increasing my target cr as you suggest. If my 396 tolerated boost and ran fine, clearly cylinder pressures weren't on the ragged edge yet, even at 10.25, even with the small cam. As a side point... can't remember where, but I read a quote once in reference to cr's in restrictor plate racing engines that I thought might apply to a big engine/single (restrictive) mixer combo. It went something like "If you have to restrict the air that makes it into the cylinder, you better squeeze what does make it in there really, really hard!".
As for dcr, I hear it mentioned alot and understand basically what it is, but need to do more research before I could make practical use of the # myself. I can't remember the exact number, but I do remember my 396 cranked with 200psi or a touch more, which I use as a bit of a baseline for what I know will work well with propane. I don't know what dcr that equates to.
Admittedly, part of the reason for smallish component selection is because of the limited airflow of a single mixer. I actually have enough spare equipment for a dual mixer setup, but the cost of a dual quad or tunnel ram manifold would be the kicker there. Maybe I'll keep my eyes peeled for a used one. I'm certain a dual setup could be tuned properly to meet all my goals, and going that route would definitely open up more options with my combo. That's one thing I'm enjoying about the forum - it gets me thinking!
In an earlier post you mentioned a combo where dual mixers on a tunnel ram was best for fuel efficiency. Actually, that made sense to me. If they were 425 mixers, splitting the flow requirements of a large engine between 2 mixers would have lowered the air gas valves to a leaner cruise position. It was a best of both worlds deal! Hmmm....

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Re: 454 Efficiency - Compression vs port velocity

Post by gottago » Fri Nov 10, 2017 3:09 pm

Its always best to consider the total package before you begin anyways and being speed talk I doubt many here are gonna be that concerned with your fuel mileage. I went the tunnel ram dual mixer route myself since I learned of that other fellows experience. I didn't really believe it all myself at first and even staged the mixers with progressive linkage thinking the mileage would be better. Nope, they worked better, more power and mileage with both mixers opening at the same time and rate. I'd run the same engine previous on a single 4, no comparison.
"If you have to restrict the air that makes it into the cylinder, you better squeeze what does make it in there really, really hard!".
I have a friend who went that route, 408 ford single mixer small cam. Runs it with 250 cranking psi on aluminum heads. Again great power and mileage but waay too much power at low rpm compared to upper end. Ended up retarding the cam which helped... 19 mpg..

I run 225 cranking psi on iron heads with a fairly normal timing curve. I suspect if you could maintain 210-220 cranking psi using a cam choice that maximises the power band where you want it, you'd be fairly safe and have a nicer driver. All the parts need to be considered and chosen as a package to get there. Brother who runs a 454 propane at 11.5:1 /medium cam/ says he liked the 110 lsa cam over previous. Not sure what that one was though. I'd run your #'s through Vizards down and dirty cam selection process just to see where max torque was and then tailor from there..

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