Max Dynamic CR with 92 octane and sea level?

[wsutard]

Anyone have advice on the max dynamic CR I should build for with only 92 octane available and running between 0-500 sea level?

 

[Yatzee]

Anyone have advice on the max dynamic CR I should build for with only 92 octane available and running between 0-500 sea level?

Pretty much anything you want because that's not such a high area that timing won't take care of any anomolies you may encounter. Octane might be an issue but at 10:1 you should be OK. Besides, due to climate warming, you'll be at 0 feet above sea level in the very near future and wished you had built a submarine instead.

 

[IQ52]

Ouch, 10:1 dynamic might be just a little severe.

 

[Kern Dog]

Yatzee, piss off with your global warming crap. Go to facebook where weenies like that want to cry, whine and be ineffective. We have no tolerance for wimps here, we are just REAL men with REAL cars, guys that eat red meat, drive Mopars and have sex with WOMEN that were born as female.

 

[66chargerpat]

 

[moper]

For me it all depends on the parts being used. What's the build you're considering?

 

[BDF6]

That was VERY insensitive of you Kern Dog, and now you've hurt Bruce's feelings.

Let's get back to the compression ratio now, ok?

 

[m79ded]

Ouch, 10:1 dynamic might be just a little severe.

Alot severe LOL!!!!!!!!!! On 93 pump gas I found that 8.5 Dynamic on Cast iron heads with manifolds as the limit. 9.0 with aluminum and headers

 

[451Mopar]

Dynamic is helpful, but won't really tell you just how high you can go. Too many variables.
I have heard of a few with around 9.0:1 (around 190+ cranking pressure)?
For me, around 8.0:1 (around 165 cranking pressure)

 

[lewtot184]

i'm in the 8-8.5 range max. stay a little conservative starting out and keep in mind a carbon build-up will increase cylinder pressure as the engine is used.

 

[lewtot184]

this has got me thinking about the engine in my '65 coronet. the dynamic number is probably low 7's, maybe close to mid 7's with carbon. this engine is very pump gas happy but has a decent tune-up. more power than I need and happy it's not in the 8's.

 

[wsutard]

440 and it will have aluminum heads and all the standard speed parts. I would like to pull as much HP and TQ out of it as I can without being on the bleeding edge. I am going to be building this from scratch so I have the opportunity to select the right parts and machine work to get the most I can, safely out of the 440.

 

[lewtot184]

the engine in my '65 coronet was put together with pump gas being a priority. I use icon 836 pistons and 82cc edelbrock heads with a fel-pro 8519 gasket. compression ratio was 9.75:1. carbon build up is going to get that ratio well above 10:1. I would have never built a 10.5:1 engine for a cruiser; I don't think they are long term reliable with pump gas. keep in mind that only .010" of carbon build up adds 1/2 point in compression. I don't get much into the dynamic ratio thing. there are way too many factors that effect the ability to run pump gas than dynamic ratio alone. dynamic ratio to me is a moving target; kinda like carb cfm ratings.

 

[Dennis H]

Now I get it, will my car run on pump gas. 91 crap gas here. 9.5:1 with about 500 at the crank runs good here at sea level on pump. No additives ever for octane. Forced to use ethanol.
No knock even at roll on in higher gears.

 

[moper]

Builders will vary in opinions on what to do. As for me, I'm at sea level and most of the year we have 10% ethanol in the pumps. I build for tight quench, and I fully machine my engines to get everything "right" (by my definition). Compression ratios are fixed - that is the volumes won't change once the parts are in place so the ratios are constant. But you have to remember the amount of charge in the cylinder will change with rpm and throttle setting. So dynamic is fixed, but the pressures that are created by that ratio increase with efficiency. a dynamic ratio of 9:1 may be ok at starter cranking rpm. But at 5K it's way past detonation threshold. I use what some consider too-tight quench distances but everything including the crank (indexed and stroke corrected) is blueprinted on top of the line equipment by great machinists to make sure parts are where they need to be so I can do it reliably.
So knowing that - I would use a hypereutectic or forged flat top piston brought proud of the deck .005", the .039" compressed head gasket, and a closed chamber aluminum head. Compression ratio is set by the chamber size in my builds. Static ends up around 10.2:1, dynamic is around 8.1 using a camshaft that will build big low and mid range power. That's how I'd do it.

 

[Dennis H]

I am here to learn. Any knock issues in the past were at lower RPM's. Dyno says no more power after 4850.

 

[lewtot184]

I am here to learn. Any knock issues in the past were at lower RPM's. Dyno says no more power after 4850.

chassis dyno? peak horsepower on a chassis dyno won't be at the same rpm as an engine dyno. takes power to drive all the parts as the drive train increases in speed. I don't pay much attention to horsepower numbers on engine dyno stuff anymore. I will take notice of comparing parts or combos on a given engine. the only power that means anything is where the rubber meets to road.

john erb of kb pistons wrote some good stuff about compression/detonation. kb website may still have it.

 

[Dennis H]

415 RWHP Chassis Dyno. Everyone I know flirting with 13:1, even over 10:1 spends way too much time hunting for or carrying race fuel. Not worth it if you really drive the car. OK for race cars.

 

[HT413]

FWIW, my 451 with Source heads, 10.49:1 static, mid 180’s cylinder psi (warm) and 0.057 quench... runs great on 93. Can’t remember the dynamic. Was rattling a little in the upper RPMs but the timing was a little advance... now that it’s right at 36 all in, she good.

 

[moper]

Detonation is not always audible. And once it starts, it will not stop until the load is removed (let off the throttle). Best way to check for it is use a lighted magnifying plug reader and look at the porcelain for bits of piston, or if it's a race car during teardown the backs of the rod bearings. You will be WAY ahead of the game by leaving compression on the table so you can run cheaper fuel, and build more power into it in other ways.