You may be right on that, but I was told differently years ago

 

exactly this. The climate and conditions the engine is run (myrid factors) affect headroom for compression and octane. Some factors are: ambient temp, humidity, elevation, oil temp, coolant temp, gear/time spent under depression (consider boat engines which maintain full load for extended periods, these engines have different requirements), combustion chamber design, piston design, head/block composition, cooling system design (the LT1 in 1993 used high compression thanks to a cooling system mod)


randoms posting that "yeah 11.5:1 is fine on 91" has multiple consequences, the first is none of them truly knows how far he/she is from the threshold of detonation, the second is that as you can see from the factors listed above, every situation is going to vary, from climate to elevation to fuel quality (not all 91 are created equally, nor is there 100% chance you wont get bad gas one day).

 

Thank you for not posting a "one size fits all" like most. refreshing lol

 

So maybe 11.1 is a safe compression? What would you suggest?

 

You should be able to ask the lifter vendor what preload they recommend. It's honestly your best bet. The vendors here are awesome about answering tech questions.

I'm on a phone so I can't post the link, but it's on either the second third or fourth page of gen 3 internal engines. Basically, yes to your question. You want to find the length you have zero vertical movement. Then add the recommended preload. You'll probably be near 7.400" but you can never be certain.

 

I finally understand what you were trying to tell me now. Tighten rocker to spec. Find zero lash with pushrod tool. Measure pushrod length with calipers. Then add the manufacturers recommended preload to the measurement. You guy's were a major help on this. Thanks for sticking with me. I appreciate it.

 

That's it!! Always glad to help

 

Ah, you are asking me for a recommendation? I'll need a ton of info, such as,

#1 Is the car a daily driver or race car?

where do you live? does it ever hit 100*F outside? Does your car sit in traffic with the A/C on, and if it does, do you ever run it hard in those conditions? What kind of cooling system is in your vehicle? How many fans, where are they, how many Liters of coolant does your system hold, where is the A/C condenser located (behind rad?) Are you planning any forced induction? Are you planning any more modifications? Are your internals OEM? How many miles on the engine (or are you using all brand new parts). Will there be a forged piston? What is the manufacturer's recommended piston/wall clearance, and what is your true piston/wall clearance measured with a dial bore gauge? What alloy is the piston you are using (the mft. piston/wall will tell us this). Is the block aluminum or just the heads? What is your bearing clearance as measured at the crankshaft journal? What kind of performance head are you using (what CC are the runners), and camshaft duration? What is the maximum RPM you anticipate? How shrouded is your intake filter (is it crammed in the bay or is it near the outside air)? DO you run an OEM hood? Does it have the OEM insulation still intact? Are you planning on running any heat shielding/reflective surfaces to direct heat away from the engine/intake? Is the exhaust coated? Can you wrap the exhaust? Is the OEM plastic panels below the engine bay intact?
Do you have access to 93 or only 91 where you live?
Are you against water/meth injection systems (as a precaution)
Do you run the car hard through all of the gears often?

#1Is the car a daily driver or race car?


And finally pictures, i need pics of the bay/engine setup as much as possible.

Answer as many as you can, don't need it all.

As an example, the closer you get to this scenario, the closer to 10:1~ I would stick:
the car is a daily driver
the engine is using OEM bearing and cast or hyper pistons with a tight clearances and light oil
there is no future forced induction plan

then this is what we desire:
-RPM (and thus cam/head) range will be minimal to preserve the OEM bearing (6500~rpm MAX in most cases)
-engine will be allowed to heat soak like OEM, cooling capacity can be minimal, operating temps are 210*F~ for economy and longevity, the transmission will be 'delicate' (no fancy expensive clutch, no high stall converters and trans-brakes)
-competition is minimal (its a daily driver) so we give up compression for longevity and ease of operation (you can ignore the engine and just drive the car, instead of worrying every time you drive it that you might hear pinging/knocking)

now, if you came back with something like, "high altitude, always cold outside, never sits in traffic, not a daily driver, no a/c, has coated exhaust and a nicely fabbed intake filter tube, loads of cooling hardware, fans, reflective surfaces, huge coolant capacity, etc..." then you can start bumping up the compression.