Wondering how everyone feels about 11 to 1 on the street with a SBC with alum. heads?

What tuning issues are we concerned about here?

What is your reasoning for running that compression? If you want to run a mild cam forget it. If your going to run somthing in the 290 advertised and over range youde probably be allright if... you keep your temps down, have a good combustion chamber, have a good ignition and have enought gear so your motor isnt lagging and working super hard. I run 11.1:1 and i can run on 89 octane all day and at the track, but i keep my temps down, i run a digital 6 ignition, have plenty of gear, and have good CNC chambers in my brodix RR200's What does your combo look like? This will help alot with the answer.

Don't really have a combo yet. Just trying to figure how much compression I can get away with.

I have good gears, 4:10's and a 4 speed.

Brand new rad with a new electric fan. Believe it pulls 2500 cfms.

Thinking about stroking my 350.

look in electrical, in the basics sticky. There is a link to PatK's DCR calculator. Run the numbers for the combo you're thinking of. More than 8.5:1 dcr is trouble on pump gas. Most shoot for 8-8.1:1. Camshaft (intake close point) plays a huge roll in how much compression you need.

I know for a fact you can do it, but like Nick said you need enough cam. I ran the Comp Magnus 294s with 11.3:1 and it ran on pump premium just fine. Now I run a 286/294* solid roller and get away with that on pump gas.

Its all in the cam . . . and a decent tuneup.

I know for a fact you can do it,
Its all in the cam . . . and a decent tuneup.


YUP :thumbsup:


bob

In a pinch mine will run on 89 and mine is 11.4 to1 , with a solid roller and fuel injection .
Mark .

right now im running 11.32 on Iron heads with 250/262 @ 50, I did run 11.57 in my last setup with comp 280 magnum and had no problems but its a 93 octane only to be safe althoough I did run 89 a few times.

Mwilson,

It's interesting b/c I'm reading here where if you get these older cams up in the compression range they were meant to be ran at in the FIRST PLACE, that they run like bats!!

And the old CC 280 Magnum isn't ALL that big of a hy-cam, but just look how GOOD compression make's it run, imho..................

And I bet onna the old suckers will run 50,000 miles or moreif the motor is half taken care of too.............

pdq67

In my first 1969 back in the day I was running 12.5:1 in the 396 BB. That car had an electric fan, 4 core radiator, THM400 w/ a full manual reverse patter valave body. The gears were 3:73 in a 12 bolt. It ran cool all day long in rush hour traffic. And I could drive that car 30 miles one way to work and 30 miles back. I did that for about a month while my 1984 Z28 was getting work done. The cam was a comp cam 292 duration with a 544 lift. Maybe it was 524 lift. That was 13 or 14 years ago so it was a long time. I ran racing gas at first. Poeple thought I was nuts because I was paying gasp $3.50 per gallon which is nothing today. I had cast iron heads, dual plane intake with a holley 750 single pumper vac. secondary carb. The ignition was a well built HEI. That car ran and ran well. It was awesome and a total sleeper. After a while I was mixing 94 octane (they sold that then) and the racing gas which I think was 112 octane. I think it had lead in it too as the nozzle was the big one. Man I miss those days.

The 1969 I bought a few months ago is a turd.

You can run 11:1 on the street depending on the goodies. If it's a small block I would not recommend going to much larger than that. I even think that's the most comperssion you could get in a late 1960's factory muscle car like a 1969 Z28.

yeah Im sure the dynamic was up there with that one!

Don't really have a combo yet. Just trying to figure how much compression I can get away with.


What do you mean by 'get away with'?

What do you mean by 'get away with'?


yeah you need to know what you want, to run 11-12:1 on pump gas you will be running a cam that requires steeper gears and higher stall converter which may not match your ultimate goals. Decide what you want with the car then make the most power you can within those restraints.

AH,
Like the other say run a cam with a late intake valve closing point, lower rear end gears, but if you are building an engine have the block zero decked and set the quench at about .032". This will help too.

Regards

CurtiSS 69

set the quench at about .032". This will help too.
Regards CurtiSS 69

Id say .035-.038

Cool! Lots of good info here.

If this is so doable, why the heck is everyone (included machinist) getting nervous when you say anything over 10 to 1 on pump gas.

Sounds like all you need to do is be careful!

Very true!!

It's the total combination, (motor AND car), and tune right-on thing to me..

pdq67

why the heck is everyone (included machinist) getting nervous when you say anything over 10 to 1 on pump gas.
Sounds like all you need to do is be careful!

Anytime someone says "Yes it will work" they will hear it if it doesnt even if its the car owners lack of tunning.

How hard can it be to tune the car!!! All you have is cooling, plug checks, jetting, idle mixture, and ignition and timing. Don't think I missed anything. Gee, we aren't talking rocket science.

How hard can it be to tune the car!!! All you have is cooling, plug checks, jetting, idle mixture, and ignition and timing. Don't think I missed anything. Gee, we aren't talking rocket science.
When you get "close to the edge" proper tuning (with a carb) can be VERY hard. Carbs are typically full of "lean spots," "rich spots" and "transition problems" at various load / throttle points. Proper tuning may require drilling idle and main air bleeds, and power valve channel restrictions.

EFI on the other hand (note Mark.L.W.'s post) doesn't have these issues.

An example, my 04 Silverado SS is perfectly happy and giving very near 1 HP / CI output (345HP/360 CI) with 11:1 compression, very mild cam (smooth idle @ 600 rpm) on 89 octane gas.

You'd be VERY hard pressed to get a carb motor to do that.

11:1 is no problem,, IF YOUR CAM IS BIG ENOUGH.
Head Material means NOTHING.
Iron , aluminum, brass or titanium,,,, the head has 180* water on one side and 1000* fire in the chamber. Material is IMMATERIAL. Its a falsehood spewed by "journalisT" who couldn't find a real job and went to work for a car magazine.

Jim, you bring up good info to study.

hhot71, very interesting comment. I had a machinst tell me yesterday that 11 to 1 in a SBC or BBC was not possible with a iron headed motor.

I agree with Hott71 on the head material issue, too, tho I've never tried to prove it.
Since it's true that alluminum will transfer heat faster than iron, it makes sense that the warm up or cool down characteristics would be different. But once everything is stable at operating temp, what's the difference?

I agree with Hott71 on the head material issue, too, tho I've never tried to prove it.
Since it's true that alluminum will transfer heat faster than iron, it makes sense that the warm up or cool down characteristics would be different. But once everything is stable at operating temp, what's the difference?

That makes sense there, and I have run 11.57 on Iron heads so I know there is no problem, I may try more next year (12:1?)If I get the funds for a 383.

I used to run 22:1 on the street on 25 octane fuel...

I used to run 22:1 on the street on 25 octane fuel...

Yeah but you were still in the 13's!

It was a solid 12-second car.

n/a aspirated 11.8 to 1 motor here (10 90s on pump 91non camaro though:clonk: ) although its at 8000+ft density alt. also small bore/flat top-small cc chamber helps cut down on detonation tendencies its all about the camshaft and,chamber shape ,quench:)

It was a solid 12-second car.



12.98 with a tailwind! LOL

n/a aspirated 11.8 to 1 motor here (10 90s on pump 91non camaro though:clonk: ) although its at 8000+ft density alt. also small bore/flat top-small cc chamber helps cut down on detonation tendencies its all about the camshaft and,chamber shape ,quench:)

10.9's at 8,000ft !

YEP UP IN HERE IN NO AIR LAND ITS USUALLY OVER 7500 FT DENSITY ALT .Mwilson ,i take that exclamation point in your post as a compliment, thank you:)
nick@NER

i take that exclamation point in your post as a compliment, thank you:) nick@NER

Yep thats great with a 35X ci motor even here in the lowland!

well that motor in my car is pretty scienced out:clonk: .ive built/ran this combo for years in customers car and my old nova so i kinda just tweaked on it and with some little tricks here and there;) , along with better heads and tuning ,i kinda knew what to expect. a guy i see at the track once in a while, runs a nova .it weighs 2700pds. w/ a 360 inch motor, runs 10.20s all day long .sure is fast huh .i guess little motors arent dead yet:)

Keep in mind guys your altitude effects your cylinder pressure. The higher the altitude the less air in the cylinders to compress to begin with. NER's 11.8:1 at 8000' is probably more like 10.5:1 in 1000-2000' air.

Good times NER -- must be a well thought out combo. Care to share the details?

sure eric ill tell some of it ;)
well its a 360 in
4.030 bore et 11.8 to 1 mech comp
crower rods lightened trw
piston steel crank
plasma moly ring
clevite bearings
comp solid roller 630 lift after lash
ported alum heads 295int-225exh at 600 in .(my bench is pretty stubborn)
ported super victor 950 hp
step headers into 3 in ehx w flowmasters
9 in converter w 4.30 gear
28 in slick @2950 pounds
nothin fancy just lots of prep(block, crank ,brgs ,head ,etc,;) )
and lots of trial and error(for what its worth, same basic combo w more gear and converter runs low tens in friends stock eliminator car. lotsa of oil control and min friction is key)

Yeah, as they say, the devil is in the details ;)

There should be plenty info on this in the "old" stuff if you search, but no need really the answer YES. I was sorta chumpish at engines when I first built and tuned mine, and it ran without ping on 92. Now I have gotten much better and it runs stronger and will haul balls with 89, I actually ran it one hot day at the track and didnt slow down or ping. I ran 87 octane last winter because of the cool air temps it never had a problem, wouldnt race on the 87 though.

I cleaned up the combustion chambers, probably helps a bit. I think all the new head designs have great chambers and would welcome 11/1 on the pump gas with a nice size cam and tune as meantioned, dont forget about the longer connecting rods, its supposed to help, thats the route I took but can cost you depending on where you are in the project.