Compression?

[Casey]

While finishing up my build I ofter reflect back at what I have learned over the years. My good friend Jim has showed me his views and experiences over many years and we tech on all sorts of things. As I read comments on the lounge I go crazy trying to figure what my car will run in the quarter mile. I am a pump gas (cali 9 to1 motor) guy and I always hear about the 10 to 1 motors hauling some ass. Is the step up from 9 to 10:1 that big of a difference?  The question is :

If you had 2 identical cars(weight, gears..everything) and they both had say 180hp witch car would get to the 1320 mark first? THE DIFFERENCE BEING ONE CAR HAS 180HP AT 9:1 AND THE OTHER HAD 180HP 10:1.(same size motor)  Let’s gust say it could happen. 
What are your views guys. Thanks, Casey.

[Jim Ratto]

what's up Casey? 
I ran around with a 11.0:1 motor for a few months, got really sick of big cam, race gas, etc....  yanked it. Got so sick of car I almost sold it for peanuts.
I personally think 9.0-9.5:1, with the right amount of cam timing, nice chambers, and of course good tuning is about the ragged edge for a street motor that is DRIVEN on our piss-gas. Too low and the carbs over feed the motor and are a real bitch to jet. Too high and load conditons you hear the motor ping and ring like a bell. On some really hot days, I have heard a litle ring-a-ping out of my motor on acceleration phase.... probably need more accelerator pump nozzle. I could back timing down, or swap back to non-projected-nose plugs, but the car runs too well otherwise, so I'm just gentle with it in the hot weather (I want to look into larger or drilling my 50 nozzles).
9.0-9.5:1 needs long-ish cam timing to help motor keep cool, my opinion. I remember first time I went above 9.0:1 and was amazed how easy the carbs were to set, and how crisp the exhaust note was.... it barked instead of bogged.

Really, high CR makes HP for a race motor, but for the street, again, how fast do we need to go? 

[louisb]

I don't think there would be a difference. Possibly depending on torque curve and gearing.

Raising the compression will increase you hp., but I don't think the difference is that much. I think the rule of thumb is 2% for each point up to about 13. So, if you had a engine making 200hp at 9:1 then you would make approx. 204 @ 10:1. (think I got that right)

For a street car I don't think it is worth the trouble to raise it too much.

--louis

[BeetleBug]

I don't think there would be a difference. Possibly depending on torque curve and gearing.

Raising the compression will increase you hp., but I don't think the difference is that much. I think the rule of thumb is 2% for each point up to about 13. So, if you had a engine making 200hp at 9:1 then you would make approx. 204 @ 10:1. (think I got that right)

For a street car I don't think it is worth the trouble to raise it too much.

--louis

Here is the math I have used;

Increase in hp based on increasing the cr;

From  6:1 to 7:1  = 5,20%
   -     7:1 to 8:1  = 4,40%
   -     8:1 to 9:1  = 3,54%
   -     9:1 to 10:1 = 2,96%
   -   10:1 to 11:1 = 2,43%
   -   11:1 to 12:1 = 2,19%
   -   12:1 to 13:1 = 1,80%
   -   13:1 to 14:1 = 1,21%   

Best rgs
BB     

[drgouk]

Hi Casey,
             Im Jim's mate from New Zealand. I brought a tranny of Jim way back when you use to help him and later on he re did a berg 5 i was having trouble with. I  need to give Jim a call and thank him for his recent help and advice that he gave me, He's a top bloke.
I can remember taking to Jim ages ago and he told me that his was helping you with a motor, I can remember that it had a 84mm flanged crank, Did you do the centre thrust conversion?
My 2332cc engine runs 10:1 with a engle K10 and pauter 1.4 rockers, but we have 98ron gas over here. It made 196hp
Say Hi to Jim when you see him.
Good luck with you New motor, will it be going on a dyno?

Regards

David Gouk

[Casey]

Thanks for the replies guys. Ratto you are a wealth of info my friend. Soon I will be able to hang with you and pick your brain.  David your voice sounds very familiar. Jim has spoken of you many times. My 84 does not have the center trust. Just the reg BMW style bearing. When assembling it, only had 5 or so thou of end play. Roger Crawford ground it and polished it up for me. I would like to dyno at Rogers, but money and time are not on my side. More importantly I want Jim to break the motor in! See ya, Casey.

Oh yeh, BB and LouisB, thank you for taking the time to reply!

[ugly duckling]

my littelen seemes to be ultra happy on 10.2 its never seen that pricey lazy racin fuel and it never will. and yes its driven actual miles.i could probebly up it a few more points on the comp and still be ok. but if the pump gas gets any higher in price i dont know what i will do. maybe propane or alky. good luck with your project.  UD.

[Germanlkmanx]

my littelen seemes to be ultra happy on 10.2 its never seen that pricey lazy racin fuel and it never will. and yes its driven actual miles.i could probebly up it a few more points on the comp and still be ok. but if the pump gas gets any higher in price i dont know what i will do. maybe propane or alky. good luck with your project.  UD.

That's making some smoking power! What's your set-up? Looks cool too!

tom

[ugly duckling]

i hope no one took my lazy racing fuel comment to personal i dont mean it that way. racing fuel has its place in certain combinations no doubt and works and it always has.   UD.

[Casey]

Jeff, would you run that same compression in a more traditional motor like a 2275? Also since you showed it, how much cost goes into pulling of a 3 liter build up? Starting with nothing. I think these babies will be the feature for sure! Thanks, Casey.

Good point on the price of gas. I sure scrathing my head.

[ugly duckling]

jeff whos that? my name is ugly duckling. to reply i wouldent see a problem with the smaller CI engine on 10.2 just as long as your induction is in order. cam rockers heads and carbatooters. at least a 94 bore engine alows you to put somewhat of a large intake valve in it. take care casey.  UD.

[Jim Ratto]

UD that was your bad ass black car "4INBORE"? I pulled in parking lot and noticed it right away.
is that the motor from the blue car?

[ugly duckling]

hello jim good see ya the other night. thats my freind tims car. take care.  UD.

[58vw]

hey ud......next engine.....16 to 1 ha ha come on, a little race gas would be fun....lets put the street motor away...besides race gas smells better