Previous Thread
Next Thread
Print Thread
Page 1 of 2 1 2
High compression in a big inch street motor #2834266
10/18/20 04:05 PM
10/18/20 04:05 PM
Joined: Jun 2016
Posts: 411
Washington
H
hemienvy Offline OP
mopar
hemienvy  Offline OP
mopar
H

Joined: Jun 2016
Posts: 411
Washington
My guess is that this belongs in the Race section.

For those that have a BIG inch street engine, at least 500 inch if not 572, with high compression,
say above 11-11.5 to 1, if not above 13:1.

Under WOT, these engines will typically make so much power that, when driving on public streets,
you really only very rarely actually use WOT. So if you are mostly putting around under part throttle high
manifold vacuum conditions, isn't this what actually allows the engine to not detonate on pump gas ?
Not so much a big cam bleeding off cylinder pressure, but high vacuum conditions ?

At some point (manifold vacuum), a 14:1 engine at part throttle will make less cylinder pressure
than an 8:1 engine at WOT, and therefore will not require race gas octane.

But if the engine is big enough, even at high manifold vacuum it will make "enough" power for
spirited street driving. A "restricted" engine.

Isn't it true that even a long duration cam will still show high manifold vacuum with the throttle mostly closed ? Above idle that is.

By the same token, if you actually are at WOT for some time interval, maybe 5 seconds, the engine will indeed
build enough heat to then require much higher octane at that point.

Somewhere in here I have a question, I don't think I'm putting it into words very well.

Re: High compression in a big inch street motor [Re: hemienvy] #2834280
10/18/20 04:45 PM
10/18/20 04:45 PM
Joined: Aug 2005
Posts: 607
Southington Ct.
T
turbobitt Offline
mopar
turbobitt  Offline
mopar
T

Joined: Aug 2005
Posts: 607
Southington Ct.
I don't think I have the appropriate info for you but I can give you a reference point. My 11:1 572 Hemi with a solid roller with 260+ duration on a 110 LSA gives me about 9 inHG at idle. Seems to run OK on pump gas.

AG.


1970 Challenger w/572 Hemi street car and my pride and joy. 1986 T-Type with 272 Stage 2 Buick V6 engine - True 8 second street car. Just updated the engine and put down 928 HP @ 35# boost to the ground on chasis dyno. 1976 Cee Bee Avenger Jet Boat - 460 Ford powered.
Re: High compression in a big inch street motor [Re: turbobitt] #2834284
10/18/20 05:04 PM
10/18/20 05:04 PM
Joined: Jun 2016
Posts: 411
Washington
H
hemienvy Offline OP
mopar
hemienvy  Offline OP
mopar
H

Joined: Jun 2016
Posts: 411
Washington
Turbobitt, do you ever floor the throttle for more than 5 seconds ? No audible detonation, probably impossible to hear though.
Must be a nice Challenger you have !

Re: High compression in a big inch street motor [Re: hemienvy] #2834294
10/18/20 05:50 PM
10/18/20 05:50 PM
Joined: Jan 2003
Posts: 27,679
Oregon
A
AndyF Offline
Too Many Posts
AndyF  Offline
Too Many Posts
A

Joined: Jan 2003
Posts: 27,679
Oregon
Um, maybe. Talk to some of the high power Drag Week guys and see what they do. They have high compression race engines and they drive from race to race. I think they use a few tricks such as changing the timing and/or the carb when they are on the street. I guess it all depends on what you're trying to do. My Duster has a 600 hp pump gas engine and it doesn't need anymore power. I don't even go WOT with it on the street. I took a buddy for a drive the other day and rolled into the throttle a bit. Looked at the data logger when I got back to the shop and at 75% throttle we went zero to 80 in four seconds. No real need for me to have anymore power than that!

Re: High compression in a big inch street motor [Re: hemienvy] #2834300
10/18/20 06:12 PM
10/18/20 06:12 PM
Joined: May 2004
Posts: 11,131
Taxes & Virus's R-US, NY
Dragula Offline
I Live Here
Dragula  Offline
I Live Here

Joined: May 2004
Posts: 11,131
Taxes & Virus's R-US, NY
My 11.6:1 big inch 605 Hemi has been fine on 93. Its a cast iron block, alum heads...I suspect I could go 12:1 no problem...And WOT on the street is not happening....roads around here have a crown on them for snow, and they are not friendly to big tire cars....


'71 Duster 400/512
https://www.youtube.com/watch?v=Znuo3jMUXTk (6.00 at 114.05mph)
https://www.youtube.com/watch?v=Y9hxSMAWoII (9.66 at 139mph)

'70 Cuda, Plan C....605 Hemi
https://www.youtube.com/watch?v=WYw6RA-k5Bk (6.25 at 108.75mph)(823hp and still tuning)
https://www.youtube.com/watch?v=JCvfzsC4NgM (9.9)
Re: High compression in a big inch street motor [Re: Dragula] #2834319
10/18/20 07:02 PM
10/18/20 07:02 PM
Joined: May 2019
Posts: 125
Lake Villa Il
INTMD8 Offline
member
INTMD8  Offline
member

Joined: May 2019
Posts: 125
Lake Villa Il
For the most part yes, I understand what you're saying and I'm sure you could run big compression at low/no load no problem.

For me, I don't want the feeling that if I want to load it up on the throttle I'm knocking the botttom end out of it because there's not enough octane to do so.

Could you build it to drive on eggshells? Yes I think so, but I'll pass on that.

Re: High compression in a big inch street motor [Re: hemienvy] #2834328
10/18/20 07:25 PM
10/18/20 07:25 PM
Joined: Jan 2007
Posts: 6,954
Mt Morris Michigan
mopar dave Offline
master
mopar dave  Offline
master

Joined: Jan 2007
Posts: 6,954
Mt Morris Michigan
Not sure where the limit is on pump gas cruising, but i would think 13:1 is gonna want more than 93. Depends alot on the cam. I have a 12.5:1 511 and just keep good gas in it at all time because i'm in the throttle all the time on the street. I do all my wide open testing on the freeway now because the car will run 60 to 110 in 4.5 seconds. I only use a 100 octane mix of 1 5 gallon can of Dragon 110 to 10 gallon of sunoco pump 93. I use to run it on 93 pump when it was 11.25:1 compression no problem. My cam is only 270@50.

Re: High compression in a big inch street motor [Re: mopar dave] #2834353
10/18/20 08:38 PM
10/18/20 08:38 PM
Joined: May 2004
Posts: 11,131
Taxes & Virus's R-US, NY
Dragula Offline
I Live Here
Dragula  Offline
I Live Here

Joined: May 2004
Posts: 11,131
Taxes & Virus's R-US, NY
Dave, yours is probably right at the limit. Other than testing I do not know how you figure it out. The wedges only seem to tolerate about 11:1 on pump at WOT with full timing...


'71 Duster 400/512
https://www.youtube.com/watch?v=Znuo3jMUXTk (6.00 at 114.05mph)
https://www.youtube.com/watch?v=Y9hxSMAWoII (9.66 at 139mph)

'70 Cuda, Plan C....605 Hemi
https://www.youtube.com/watch?v=WYw6RA-k5Bk (6.25 at 108.75mph)(823hp and still tuning)
https://www.youtube.com/watch?v=JCvfzsC4NgM (9.9)
Re: High compression in a big inch street motor [Re: Dragula] #2834364
10/18/20 09:13 PM
10/18/20 09:13 PM
Joined: Jan 2007
Posts: 6,954
Mt Morris Michigan
mopar dave Offline
master
mopar dave  Offline
master

Joined: Jan 2007
Posts: 6,954
Mt Morris Michigan
When i was on pump 93 with 11.25:1 i could only run 1/8 mile wot runs on the back roads, so short passes and no sign of detonation on plugs. Now at 12.5:1 and 100 octane, no sign of detonation of plugs yet. This Dragon fuel(Terragon 110) is really 113. Don't understand their rating. I don't hear and or see it on plugs.

Re: High compression in a big inch street motor [Re: hemienvy] #2834417
10/19/20 12:20 AM
10/19/20 12:20 AM
Joined: Aug 2003
Posts: 35,749
Bend,OR USA
C
Cab_Burge Offline
I Win
Cab_Burge  Offline
I Win
C

Joined: Aug 2003
Posts: 35,749
Bend,OR USA
Me thinks your playing with a bag of deadly snakes messing with high compression and todays pump gas tsk
Theory and talk is one thing not directly tied to the real world and real world results twocents
My current S/P car runs on E85 with 15 to 1 compression and that would be the only fuel besides race gas I would build a motor with more than 11.0 to 1 compression to run on the street today regardless if hemi or wedge, Mopar or any other brand motor with aluminum heads twocents
I am going to build a pump gas 572 C.I. wedge motor with no more than 11.00 to 1 compression with a set of B1 heads on a new KB aluminum block, I'm hoping to exceed 800 HP on today pump gas safely luck
My last serious pump gas car made 612 HP with 9.25 to 1 compression with iron heads on a stroker 400 block with 511 C.I. using CA pump swill and a low deck six pack set up, that combination ran 10.69 at 124.5 MPH through the 3.0inch complete exhaust system with the six pack air cleaner on weighing 3450 LBs with me in the car grin
I swap heads twice and ended up with a set of Indy SR M.W ports and a single 1050 CFM Dominator on the motor, I had swap the crankshaft from the 4.25 stroke to 4.300 to help gain some compression which ended up at 10.78 to 1 up That combination ran 9.993 ET at 134.7 MPH cork up with the air cleaner on boogie
I ended up swapping that car off shruggy I learned a lot with that car and motor and some times wish I had it back realcrazy
There are many ways to make power safely, there are as many ways or more to screw up good parts up trying to learn how to do it safely and properly whiney work
Can you afford to hurt parts searching for more power a new way? If not, don't try downtwocents

Last edited by Cab_Burge; 10/19/20 12:32 AM.

Mr.Cab Racing and winning with Mopars since 1964. (Old F--t, Huh)
Re: High compression in a big inch street motor [Re: Cab_Burge] #2834455
10/19/20 06:38 AM
10/19/20 06:38 AM
Joined: Oct 2015
Posts: 413
UK
rb446 Offline
mopar
rb446  Offline
mopar

Joined: Oct 2015
Posts: 413
UK
Thats the way we went with our street/strip brkt car, 589ci, only 10:1, small solid roller, 260/270@.050", tiny 950HP carb,(15" vacuum@idle) Indy 440-2, Indy heads, 33 deg total, street 4200 converter, max torque@4400, max rpm/hp 6200@traps, 4.10's with a low first in 727, fill up in the morning on the way with Shell V-power pump, drive to the track on full exhausts, race/drive home, no stress, easy on parts, heavy 3800lb car low 10's. up

Last edited by rb446; 10/19/20 06:48 AM.

1969 'Cuda 446ci, best 9.96@133.9 in 1990
1971 340 'Cuda, best 11.01@122.8 in 1987
Re: High compression in a big inch street motor [Re: Cab_Burge] #2834473
10/19/20 08:28 AM
10/19/20 08:28 AM
Joined: Jan 2007
Posts: 6,954
Mt Morris Michigan
mopar dave Offline
master
mopar dave  Offline
master

Joined: Jan 2007
Posts: 6,954
Mt Morris Michigan
I only buy Sunoco now and only at the supplier, so i think it's the best i can get in the area. I do not run on straight pump now that the compression is at 12.5. I tried it will 3 gals of Dragon 110 to full tank of 93 Sunonco and could hear detonation while street driving. From stop to moderate acceleration. Full 5 gal pail and no detonation that i see yet. From what i remember back in the day when all the cars had high compression 100-102 octane is all they had at the pump if i remember the story correctly.

Re: High compression in a big inch street motor [Re: hemienvy] #2834486
10/19/20 09:00 AM
10/19/20 09:00 AM
Joined: Oct 2007
Posts: 3,599
New York
polyspheric Offline
master
polyspheric  Offline
master

Joined: Oct 2007
Posts: 3,599
New York
W/r/t "big cam bleeding off cylinder pressure"
It does reduce CCP... all the way up to 3,000 RPM (more or less, depending on too many variables to list, but stops well before the torque peak).
After that, it increases cylinder pressure - that what it's for.
It doesn't always need 5 seconds to "build heat", the piston damage can occur in 1 second.


Boffin Emeritus
Re: High compression in a big inch street motor [Re: polyspheric] #2834516
10/19/20 09:46 AM
10/19/20 09:46 AM
Joined: May 2003
Posts: 5,813
Downtown Roebuck Ont
Twostick Offline
Still wishing...
Twostick  Offline
Still wishing...

Joined: May 2003
Posts: 5,813
Downtown Roebuck Ont
Originally Posted by polyspheric
W/r/t "big cam bleeding off cylinder pressure"
It does reduce CCP... all the way up to 3,000 RPM (more or less, depending on too many variables to list, but stops well before the torque peak).
After that, it increases cylinder pressure - that what it's for.
It doesn't always need 5 seconds to "build heat", the piston damage can occur in 1 second.


And just because you don't hear detonation doesn't mean it isn't happening.

Kevin

Re: High compression in a big inch street motor [Re: rb446] #2834533
10/19/20 10:26 AM
10/19/20 10:26 AM
Joined: Jan 2003
Posts: 16,465
S.E. Michigan
ZIPPY Offline
I Live Here
ZIPPY  Offline
I Live Here

Joined: Jan 2003
Posts: 16,465
S.E. Michigan
Originally Posted by rb446
Thats the way we went with our street/strip brkt car, 589ci, only 10:1, small solid roller, 260/270@.050", tiny 950HP carb,(15" vacuum@idle) Indy 440-2, Indy heads, 33 deg total, street 4200 converter, max torque@4400, max rpm/hp 6200@traps, 4.10's with a low first in 727, fill up in the morning on the way with Shell V-power pump, drive to the track on full exhausts, race/drive home, no stress, easy on parts, heavy 3800lb car low 10's. up


I really like this conservative combo alot, and put together something pretty close, except mine is 572ci, 10.2:1 and has hemi heads.




Rich H.
1969 Plymouth GTX
451ci B engine
11.02 at 123mph
NA, 93 octane E10 fuel, DOT tires, mufflers, no trailer
Direct Connection Tech Alumni '05 to '13
Learning without end, your influences, influencing others (all too often unknowingly until years after the fact) and the people you meet are the best part.
Re: High compression in a big inch street motor [Re: Twostick] #2834646
10/19/20 02:06 PM
10/19/20 02:06 PM
Joined: Aug 2003
Posts: 35,749
Bend,OR USA
C
Cab_Burge Offline
I Win
Cab_Burge  Offline
I Win
C

Joined: Aug 2003
Posts: 35,749
Bend,OR USA

And just because you don't hear detonation doesn't mean it isn't happening.

Kevin [/quote] iagree
Detonation versus pinging are NOT the same thing twocents scope
Pinging can hurt parts, detonation kills parts quickly hammerwhiney

Last edited by Cab_Burge; 10/19/20 02:07 PM.

Mr.Cab Racing and winning with Mopars since 1964. (Old F--t, Huh)
Re: High compression in a big inch street motor [Re: Twostick] #2834669
10/19/20 03:19 PM
10/19/20 03:19 PM
Joined: Oct 2007
Posts: 3,599
New York
polyspheric Offline
master
polyspheric  Offline
master

Joined: Oct 2007
Posts: 3,599
New York
I think we can agree that a conservative initial spark lead and a longer, slower advance curve will help here, but how much? Probably related to stall and slippage?
Add 15-20° of vacuum spark to get mileage back and keep temperature under control.


Boffin Emeritus
Re: High compression in a big inch street motor [Re: polyspheric] #2834958
10/20/20 10:57 AM
10/20/20 10:57 AM
Joined: Jan 2012
Posts: 2,046
Stuttgart, Arkansas
rickseeman Offline
top fuel
rickseeman  Offline
top fuel

Joined: Jan 2012
Posts: 2,046
Stuttgart, Arkansas
I think you can run as high of a compression as you want with pump gas if you weren't ever going to get on it. You can't make manifold pressure with the throttle closed/barely open. Powerful engines can do 60 mph with the throttle barely open. But if you floor it, it will detonate and that's bad. And it doesn't take the 5 seconds to build heat that you are talking about.

Modern high performance engines have anti-knock sensors to protect them if you put lower octane gas in them than they require. You can drive coast-to-coast with 87 octane gas in your supercharged Demon or your twin turbo Mercedes and it will not hurt a thing, but if you floor it, you can't make max manifold pressure without detonation, so the computer cuts the timing back to protect the engine.

We used pump gas to warm the engine in Big Daddy's Top Fuel dragster. I doubt you're driving a more high performance car than that.


2011 Drag Pak Challenger
Re: High compression in a big inch street motor [Re: rickseeman] #2835022
10/20/20 12:58 PM
10/20/20 12:58 PM
Joined: Aug 2003
Posts: 35,749
Bend,OR USA
C
Cab_Burge Offline
I Win
Cab_Burge  Offline
I Win
C

Joined: Aug 2003
Posts: 35,749
Bend,OR USA
What was the mechanical compression ratio on his Top fuel motors back then and how much boost would it make idling when warming it up,? Also didn't they run it really rich when warming it up?
I thought all the top fuelers warm them up on alcohol and then switch them to nitro for several minutes to make heat confused

Last edited by Cab_Burge; 10/20/20 12:59 PM.

Mr.Cab Racing and winning with Mopars since 1964. (Old F--t, Huh)
Re: High compression in a big inch street motor [Re: Cab_Burge] #2835033
10/20/20 01:19 PM
10/20/20 01:19 PM
Joined: Jan 2012
Posts: 2,046
Stuttgart, Arkansas
rickseeman Offline
top fuel
rickseeman  Offline
top fuel

Joined: Jan 2012
Posts: 2,046
Stuttgart, Arkansas
I would guess the compression was low and I doubt it made any boost to speak of at idle but we didn't have a manifold pressure gauge on the intake manifold.

I don't recall them changing the mixture to warm up.

Gasoline builds heat faster than alcohol. Then switch to nitro (but not for several minutes) to read the plugs.


2011 Drag Pak Challenger
Page 1 of 2 1 2






Powered by UBB.threads™ PHP Forum Software 7.7.1