mesterious

iTrader: (1)

I need to know if 11.3:1 compression ratio is too much for a 93 octane 406 High Performance Street motor. The Details of the Motor: Cam 249/255dur@.50 624/640 lift, .040 head gasket, and AFR 210 65cc Aluminium Heads which i havnt bought yet till i know i can run that compression ratio so i wont be stuck in a bad situation with them. Also I found a real DCR calculator and it came out to be 8.6:1 where as 8.5:1 is supposedly the limit on pump gas, is that too much?

bjankuski

It should be fine. I am skeptal on your dynamic compression being 8.6, that cam seems big and I would expect less then 8.6 DCR with an 11.3 static compression ratio. Run the numbers again to make sure you did not make an error.

86toy

you can go up to 10to1 compression on pump gas, 8.6 with that cam is a little low. most performance cams like 9.5 to 1 compression or higher.

vetteoz

iTrader: (13)

He is talking about DCR not static compression

vetteoz

iTrader: (13)

I agree.
I am running shorter dur 234/ 242 (296/ 304 ) on 12.1 CR and are at 8.6 .
I have found Kelleys DCR calc to be the most real world accurate.Download here
http://cochise.uia.net/pkelley2/dcrvb6.zip
With the commonly used KB Pistons DCR calculator my engine shouldn't be running at all

mesterious

iTrader: (1)

yeah thats the one i used the thing is, is that it asks for Advertised Duration and the for that cam it is 279/285 from lunati and there is a similar cam from comp that is 286/292 and it has 254/264?@.050 and thats why i cant get a straight DCR is cause different companys measure at different spots to get theirs. so if you could give me the correct DCR (if possible or just an est.) That would help me out alot and plus i think im going to hit 11:1 compression to be on the safe side but you tell me what you think

JakeJr

I agree! With that much cam you won't have a problem running 11.3

Jake

vetteoz

iTrader: (13)

Wrong , not all cam lobes are equal.
Closed is closed , .050 lift is .050 lift
but depending how steep ( aggressive ) the lobes are there can be lots of difference in the closed (adv ) duration even though the @0.050 duration is the same.
Exp;
Put a 6ft length of 2x4 on your front steps and a 10ft length.They both go to the same height (lift ) but the longer one starts further out having a shallower ( less aggressive ) ramp.
This is how you can dial the DCR down while still keeping the same lift @0.50 by selecting a cam with a longer adv duration.
You have no effective compression until the valve is closed

JakeJr

Yes, I've seen the same thing, even from the same cam company. Take CompCams for example; some of their cams have their advertised duration measured as .006" and others at .020" and still others differ from those two. So using their advertised duration specs isn't going to work.

DCR doesn't concern me all that much. My Engine Analyzer Pro simulation program calculates my son's DCR at 9.02

Jake
Jake

mesterious

iTrader: (1)

Crap i gave the wrong cam specs on the similar Comp cam sorry bout that i was in a rush when i was replying to your message. hopefully this will make more sense ok same ADV(286/292) but the Dur@.050 is 248/254 and .576/.582 lift. Now you probably see my confusion but i now know ill still be safe with 11.3 so its all good but you know alot more then me maybe you can edjamakate me on this adv duration stuff so next time i build a motor i wont be confused about it again.. and THANKS ALOT for helping me out!

Sonix

iTrader: (1)

11.3:1 CR
248/254 cam - solid roller?
Aluminum heads
93 octane fuel (not 91, but 93 !!)
How are you going to fuel this? Intake manifold and carb? Which ones?

How are you going to gear it?
Transmission?
Weight of vehicle?
Altitude?

What are you going to do with the vehicle? Pull a boat behind your truck at 2500RPM up a hill? (I know that's not the answer, but you get my point eh?)

mesterious

iTrader: (1)

well the cam i got is a Lunati Voodoo Solid roller 249/255 im going to back my compression down to 11:1 if not 10.5:1 but i want to make at least 550HP my tranny is going to be a T-56 new rear end with 4.10 gears 3100 pound Camaro sports coupe(Stock Carbed 305) my alititude is 750 feet above sea level my intake manifold is a Super victor and carb is holley 4150 850CFM and im in Mississippi and it gets kinda hot in the summer so i might go 10.5:1 but 11:1 seems alittle better for my goal on 93 and here all they have is 93 bairly any 92.. and its really going to be a fun car just like some on the week days then cruises if not alittle track on the weekends

Sonix

iTrader: (1)

Ok, high gears, light weight, stick shift. Big intake and carb. 11:1 should be fine. You're not going to be lugging it around in high gear, drive it like a sports car and it'll be fine. Use a cold air intake and a cooler thermostat to let it run a bit cooler, and you shouldn't have any problems.

mesterious

iTrader: (1)

ok sweet! you have answered all i needed execpt for one thing.. what degree thermostat?

Sonix

iTrader: (1)

Low = 160* typically.

JakeJr

Here's some information that I pulled from the results of the 2009 Engine Masters competition sponsored by JEGS. 30 reputable engine builders showed up with their engines to compete with only one winner. The full results are in the Feb 2010 Popular Hot Rodding magazine. (When I can I like to quote my source)

Now remember, THESE ENGINES WERE COMPETITING WITH 91 OCTANE PUMP GAS supplied by Shell, NOT 93 octane. Don't forget that little tid-bit.

Of the 30 entries, 24 of them had compression ratios 11.3:1 or higher (point #1)

Two more engines had 11.0:1 to 11.2:1 compression (point #2)

So that's 26 out of 30 engines running 11.0:1 or more with 24 of those running 11.3:1 or HIGHER. Of the 4 engines NOT running at least 11.0:1, two ran 10.9:1, one 10.5:1 and only one ran 10.0:1

Here's the kicker:

21 of the 30 engines were running camshafts VERY close to yours; either slightly less in duration or slightly more. Those running slightly more were running cams only about one size up (about 6 degrees @ .050").

The winner ran a 246/246 @ .050" and 11.3:1 CR.

These guys had built engines to compete and win the title of "Engine Master" - not to mention the $24,000.00 - so they definitely couldn't stand for any detonation, which would ruin their chances and their day.

Also it bears considering, that the engine building teams are a bunch of very knowledgeable guys, at the top of their game. To me, it shows that 11.3:1 will definitely work with your combo.

Now, as usual their will be those who'll try to pick apart those results. It Never Fails. Some guys just can't wait to HATE on posted information. However, what I've tried to do was give you documented information as opposed to opinions or guesses in the hope that it helps.

Jake

mesterious

iTrader: (1)

Wow nvm looks like im going to keep from having to get my heads milled.. Thanks alot for the write up and spending the time to help me out!! that really does help me out alot cause i would have wasted money doing something i didnt have to do.. 11.3:1 it is.. THANKS AGAIN!!

mesterious

iTrader: (1)

Sonix

iTrader: (1)

Yikes, you're ready to be blasted down eh? Not to "hate on" your information, but just to add a little tidbit? Just because "engine masters", or "nascar", or "insert tv show here" built a certain engine, doesn't mean Joe Blow can. Not just a skill matter, but also the fact that the engine masters engines are running ***** to the wall to run in a competition. The reason I asked gearing etc, was to check about the "real world" characteristics. If you load it heavily, often, then it'll wear out sooner, and be more prone to detonation.
The engine masters engines might be installed in a car, and self destruct 5000 miles down the road - they are meant to run for a few hours to win, that's it. They aren't meant for durability. That's something that street engines require, and why they aren't quite running ***** to the wall. Since the guy is building a street engine, and not a race engine, I wouldn't go "completely" all out, but of course, it's more fun to be on the razors edge