I have run NOS stock AE Hepolite pistons for over 15 years with C/R around
11:1 with absolutely no concerns.....in fact in never occurred to me that there
might be a problem. Race Gas, of course, and over 6,000 RPM from time to time.
I like using the NOS stuff where ever I can find it. In fact, for TR3/4
Cylinder Liners, I have special fixturing for reboring the old cast iron
liners.
This is good cast iron and nicely 'aged'.
regards,
> John:
>
> Hepolites are a very solid piston, so don't worry about the
> quality.
>
> As far as the compression ratio, it depends on the cylinder
> head, not the piston. The pistons are interchangeable for all years.
> Triumph machined more metal off the head for the high compression UK
> motors (9.5:1) and less metal off the head for the very low compression
> US smog motors (7.75:1).
> They will perform just fine for 10:1 compression naturally
> aspirated applications and beyond *IF* you stay out of detonation. Run
> them with detonation (pinging) and they will quickly fail. Since pinging
> is more likely with higher compression ratios, most people like to go
> with forged above roughly 10:1 compression. For pump gas and cast
> pistons, 10:1 is a reasonable upper limit, with most people aiming for
> about 9.5:1. I run 9.6:1 with no issues. I machined 0.120" off my later
> 7.75:1 smog head and 0.010" from my block deck to get to 9.6:1.
> If possible, have your block zero decked (machined to make the
> pistons flush with the top of the engine block) and then machine the
> head to make up the difference to reach your desired compression ratio.
> This will make more power and get you better detonation resistance than
> if you machine the head only. This typically means taking about 0.015"
> off the block, according to Kas Kastner in the TR6 racing prep handbook.
>
> Cheers,
>
> Vance
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