[John Milner]

Originally Posted by TransAm 474

So... Y'all think 9.8 compression will work out good for this on pump gas? If so, which camshaft for this compression? Crower 60916 or Summit 2802? The look on paper, it seems the 2802 would make it even more pump gas tolerant, do too its later Intake Closing, but it may be a bit more soggy down low in normal driving conditions over the Crower 60916, but then again, even the specs of the 2802 doesnt really look that big for a 400 CI motor with it's 114 LSA.

I ran that same exact combination once. It was a 400, 62 heads and a 2802 cam. It never overheated, never pinged and ran fine on 91 octane. The engine really pulled hard too.

[unruhjonny]

Originally Posted by John Milner

I ran that same exact combination once. It was a 400, 62 heads and a 2802 cam. It never overheated, never pinged and ran fine on 91 octane. The engine really pulled hard too.

keep in mind, your heads had larger combustion chambers.

[TransAm 474]

Thanks guys, I assume the centered pins, instead of offset, in the aftermarket pistons wont present any problems? I noticed most all aftermaeket piston pins are centered.

[Jay S]

Originally Posted by TransAm 474

Thanks guys, I assume the centered pins, instead of offset, in the aftermarket pistons wont present any problems? I noticed most all aftermaeket piston pins are centered.

It is fine. IRC, It actually increases the piston velocity some at tdc and helps the quench speed. More quench velocity is a good attribute. So is less contours on the piston top compared the the 4vr oems. FWIW, being that this is the high compression thread, our 510 cid 10.5 iron head engine I run on pump gas has flat tops with no valve reliefs and a small dish. The solid cam iron headed Pontiac we pushed compression on had oem forged piston reverse hung with the crank offset ground with a really tight quench. It was 10.4:1. It it probably had a higher piston velocity for the quench than an normal oem.

OEM’s do the offset to quiet down the engine noise some and moves the biggest forces past TDC slightly. It changes the dwell some as the piston is coming up on top dead center, moves the largest forces on the rod and crank over so the piston has more leverage on the crank. Seen different opinions on what it does with friction for what the engine is being used for.

The 2618 alloy of the icons takes more pistons to wall clearance. Engine will be noiser when cold than an oem forged or a forged 4340 alloy. 4340 (hope I have the number right) is a better alloy for your project imo. Builders run the icons all the time for projects like this though. They do have the best quench with out a lot of decking. Autotec can move the piston comp height in a 4340 alloy, so can Ross. More money though, can only say we did it.

I have built a couple engines that we reverse hung the oem pistons. Years back, was supposedly good for a couple horsepower and make pitch of the exhuast higher and louder. Lol, trying to intimidate the competition. I do not recall it changing much of anything though.

Better experts on here for piston than me, if I missed something somewhere feel free folks, correct it..

[Douglas Willinger]

How much compression ratio is feasible with iron heads, with somewhat higher octane fuel, not 91-93 with or without say 10% Ethanol, but say 95-97 octane, achievable with added octane booster.

Perhaps an intermediate blend of Petroleum and Ethanol, say, E-30, E40, E-45?

https://www.eesi.org/…/view/fact-she...ry-of-o…

"A national transition to an optimized mid-level ethanol blend, between E25 (25 percent ethanol, 75 percent gasoline) and E40 (40 percent ethanol), would lower consumer fuel costs and standardize the fuel supply. The Department of Energy recognizes that increasing the ethanol content of gasoline is a potential pathway to increasing the octane rating of the gasoline supply. A mid-level ethanol blend would enable the design of highly fuel-efficient engines that would significantly reduce petroleum consumption, reduce life-cycle greenhouse gas emissions, and help meet higher fuel economy standards. As of now, the Department of Energy and the EPA have approved the use of E15 for make and model year 2001 and newer vehicles, which account for 80 percent of the vehicles on the road today."

Also see:

https://www.frontiersin.org/articles...015.00016/full

"In addition to the octane number benefits of ethanol, several studies have indicated that complementary benefits to octane number can exist with intermediate ethanol–gasoline blends. Splitter and Szybist (Splitter and Szybist, 2014c) have shown that intermediate gasoline alcohol blends, like E30, have reduced combustion duration, and more recently Szybist and Splitter have shown improved dilution tolerance of similar E30 fuels over reference fuels and gasoline (Szybist and Splitter, 2016). Beyond flame speed and dilution tolerance effects, intermediate ethanol–gasoline blends have been shown to exhibit reduced combustion temperatures and increasing engine efficiency (Szybist et al., 2010; Jung et al., 2013b), which Szybist et al. illustrate could be a product of increased molar expansion ratio of alcohols compared to gasoline (Szybist et al., 2012). Many have indicated that the charge cooling of ethanol in direct injection engines offers reduced enrichment need (Stein et al., 2012, 2013; Jung et al., 2013a). An interesting recent study of Sluder et al. (2016) suggests that, in practice, fuel sensitivity – the fuel RON minus the fuel MON octane numbers – by default accounts for much of the charge cooling effects from direct fuel injection on fuel antiknock performance. Thus, these combined studies illustrate that the potential to increase engine performance and fuel economy offered through intermediate ethanol–gasoline blends extends beyond increased octane number alone

It was found the incremental increase in fuel ethanol content from E10 to E15 and E10 to E25 could enable fuel octane number to increase from 87 to 90 AKI and 92 to 95 AKI for regular and premium grades, respectively. Additionally, these finished fuels could be achieved by blending ethanol with base stock fuel octane numbers identical to those historically used for leaded fuels. Therefore, an incremental increase in fuel octane number from a 5 to 15% increase in fuel ethanol content could be a process that enables continued future evolutionary changes to personal mobility that comply with historically documented consumer technical and regulatory trajectories."

Notably, such mid range grades, E-25/E-45,would be adaptable to older design vehicles as those with carburetors, and hence offer a far greater spectrum of consumers.