do you think its save to run 26 thousand piston to head clearance ? has after market forged pistons and rods.
Sounds close Deck parallel? How much potential piston rock due to bore clearance? I've run lighter piston engines with shorter strokes that close beyond 8000 rpm but you're getting near contact. Not going to be a reliable method to try to calculate G force, rod stretch, piston expansion. Stock 401 nail @ 6000 rpm. (900g piston used) (327 sbc w/500gm piston @ 8000 is 5113 lbs @ TDC) Your Inertia Force is 3,692.81 pounds. Your Stroke/Rod Ratio is 0.587 Your Rod/Stroke Ratio is 1.70 Effect of Rod/Stroke on TDC and BDC inertia force: Your Upward Inertia Force at TDC is 5,860.85 pounds. Your Downward Inertia Force at BDC is 1,524.77 pounds.
You should check the clearance between the piston dome and chamber too. I've heard of Turbo Regal guys stacking the steel head gaskets, you could do that for an extra 0.015". Or have the piston machined. Might be fine as is.
I don't know on a Nailhead, but I'm at .024 on my 4.5" stroke big block in the Mustang with redline at 5800 RPM. I'm betting it's getting dang close with the piston speeds the engine achieves with a stroke that long. Excellent quench, though, runs on 91 non-ethanol octane if I crank the timing back to 30 total, 10 initial, but I'm at 3500 ft. elevation, and my custom cam is designed to bleed off pressure. It does like to have the timing dialed up to 34 total, but that requires half 100 LL/91 mix. Pistons are 4.42 bore with 22cc dish, heads are at 68-69 cc chambers.
For the RPM's your turning Joe I don't believe there will be ANY problems. The pistons are lighter than stock. Don't know about the rods. Just my thoughts. Tom T.
Yes Tom, light weight pistons, after market rods just a few grams heaver then stock. going shift at 5200-5500 rpms
Compare your example to a stock one and see if it assures comfort. http://www.wallaceracing.com/Calculate-Inertia-Force-of-Piston.php
Should be fine, but long term you should consider carbon build up. I am guessing you are running the stock type .018 thick steel head gaskets. If it's a long term build, I would just use a Best or Victor .045 head gasket. You'll lose some compression, but it's not that bad. Depends on rest of your build.
Why would you spend much effort to gain .7 compression on a fairly mild cammed engine? If you are chasing hp, I'd go really big on cam and compression and get serious rather than lose much needed margin for pump gas.
Worth 12hp @ peak according to Dyn0 2003. Sound realistic? And there is a gain in the whole rpm range. Other than the possibility of reducing detonation resistance, I don't see a downside. I'm in the same situation with my blue car.... around 9:1 but in my case I have a much bigger cam (245*). Higher cr would be a better match for the cam. I put that cam in when I was a teenager 38 years ago!
It sounds exactly like where I'd expect, and I'd rather have some safety margin when the inevitable difference in various gas stations and their refinery sources cause inaudible problems the machinists or bearing makers will get blamed for. My perspective on this was using performance vehicles in various rep. capacities and logging near a million miles on them while tracking mileage and tuning. Backing the timing down reduces both mileage and power, so there's zero advantage chasing a theoretical level of octane tolerance using compression when your fuel source changes throughout the year and by region. My philosophy on this is to go for a much bigger gain with much more cam (and compression to match, but not max out) and use your talents to tune out what others find "irritating" as far as street manners. You can definitely tune out whatever perceived poor manners at the power levels this engine is capable of NA. I don't recall his cam specs but was thinking it to be on the smallish side and at the same time the heads are flowing enough to offer 500 hp potential, so why try to find 12 hp at risk to the engine (invisibly) when there's lower hanging fruit. Just my opinion, definitely not a bash. Love the car.
f85 am with you on having to much comp for gas. on big stroke motor 446 cubic inch. am at about 10.40 compression, with the head design and the longer 6.535 rods, 3.75 stroke and high 10.40 compression it likes 28 degree timing. it has 195 cranking compression. the 401 stroke 9.15 comp that am talking about has 410 cubic inch with 6.535 rods and 3.69 stroke and likes 30 degree timing, but only has about 160 cranking compression. both on 91 octane gas.
I think it's worth the effort, but there are only so many ways to get compression. Have you decked the block/ shaved the heads or is compression all custom piston?
It's always worth effort in the planning and machining stages, I think he's at the assembly stage (?). If so...I certainly wouldn't throw that kind of money at 12 hp (or my time because I can machine things). Although not impossible, I would question decking blocks after boring, depending on how it was done. Thanks for the info and specs on the two different engines. You probably have enough info on your two examples to decide what you need to do. The cranking pressure offers a little bit of insight on your dilemma. Not knowing your cam events (intake closing degree or general specs)... I would guess that one likes 28* because any more shows the early stages of detonation, even though it has a slightly longer stroke. The other one having the same chamber and burn characteristics might be more forgiving of timing having more rod ratio, meaning less crank angle. The same things might be happening in the chamber, just that one would be more forgiving due to that and lower cylinder pressure prior to combustion. The compression trapped or static is only a starting point for octane tolerance, it's temperature (and load) that do the deed. One thing to look at is where the piston is in crank degrees at intake closing and compare between the two, and correlate your cam specs and intake closing. I don't know if these are in similar/same vehicle, gear. flash speed, etc....the point being that I think the 28* engine is showing signs of running at the limit for your area's pump gas. I could be mistaken, I don't know much info about these. The wilder one might have a higher flash and more gear... Also, without knowing your cam specs on the 9.1 engine, I'd be thinking of advancing the cam and using whatever overlap is there to benefit if you knew for a fact you could give full timing without worry. I'd do whatever I could to pump up mid range, peak torque and shift recovery rpm being that you have plenty of intake port to feed it. Theoretically anyways, the only thing you would suffer as opposed to less overlap, later cam events etc., is power 'after' the hp peak. I don't think you'd gain anything noticeable anyways, just push your engine closer to det. with the .7 compression and later timing events losing midrange and shift recovery. Just my opinion. That's a lot of thinking for ten hp.
custom pistons in hole 11-15 thousands. 3 things happen on this built. 1- thought head gaskets were .035 compressed but are .045. 2-changed to tulip valves and gained about 5 cc. i think Tom T told me you gain 4-6 cc with tulip valves. plus was going deck the block to be 4- 5 thousand in the hole but machine shop was busy and taking to long as it was, so i said forget it.
