Lowering compression ratio

[hemiEssex]

I live in the Northen part of BC Canada. I have to drive my car a long ways to get to any meets, shows or gatherings. My car is a 65 Coronet with a 68 HP 440 Engine. The compression is the stock 10:1. Car should run on 94 plus octane. 91 is around here a little bit, but 94 is hard to find. Mixing with av, race fuel etc is not practical as I frequently drive this car 8-12 hours round trips. My question is this: Is there a head gasket that I can use to bring the comp down so it will run on regular pump gas? Not only because of the cost but because of the detonation issue that I run in to with not being able to get a consistant octane level of gas for the car. Or is there another economical head that I can switch to to be able to run this thing on pump regular. I realize that I can turn the timing back but this limits the power of the engine etc. and hampers the gas mileage. Currently it get about 15mpg on the highway, I would like to get the same if not better. The motor is running a comp cam, headers, eddy performer intake, holley 670 street avenger, new dizzy from 4 seconds flat with vacuum advance, MSD box, 3 inch exhaust with glass packs. 3.25 gears and a 727 auto.
Any ideas on the cheap would be good, I have spend a sh*t pile of money on this car already and I just want to be able to drive it without hurting the motor.
cheers
Steve

 

[Cranky]

How bout installing a timing retard dial in the car so you can turn it back when on the gas hard? What are the cam specs? Have you done a compression check to see what you have? You should be able to run 10-1 with the right cam and tuneup and if you lower it, it will act about the same if you retard the timing. Imo, you would be better off using a timing retard on the MSD...

 

[Cranky]

What heads do you have? A 68 should have the 906 which have the same CC's as the 452 but the 452 has induction hardened exhaust seats. Quench...that's the problem. You don't have much. Rule of thumb is .040 from the piston to the chamber roof and with uncut heads, you have .110 with steel shim gaskets and that's only if you have a 0 deck piston..... and I'm with lewtot184. You will only increase the quench distance (ie, even less quench) with a thicker head gasket. The easiest thing to do is to control timing. You might talk to MSD and see if they have something that retards timing automatically. What are your timing settings anyways?

 

[70rr-brian]

What heads do you have? A 68 should have the 906 which have the same CC's as the 452 but the 452 has induction hardened exhaust seats. Quench...that's the problem. You don't have much. Rule of thumb is .040 from the piston to the chamber roof and with uncut heads, you have .110 with steel shim gaskets and that's only if you have a 0 deck piston..... and I'm with lewtot184. You will only increase the quench distance (ie, even less quench) with a thicker head gasket. The easiest thing to do is to control timing. You might talk to MSD and see if they have something that retards timing automatically. What are your timing settings anyways?

I think MSD has a digital e-curve distributer that you might be able to use to retard timing advance easily with a pot adjustment versus changing springs and bushings. Then dial it back in when you get some good gas. They look ridiculously easy to adjust. But i'm sure they aint cheap.

 

[shag766]

at 10-1 compression you shouldn't have a problem with the gas. i would think it is more electrical or carb. or; carry a small can of juice. i mean a 2 gal can. put a little in when you add gas. if the juice fix's it, you are running to lean. .02 cent's rick

 

[HEMI-ITIS]

You might also be able to change the cam profile and bleed off some cylinder pressure.If your on the edge of detonation,a water/meth injection system could help under heavy load or WOT.I have been looking at the Snow Performance set up.Take a look >>> http://www.snowperformance.net/product_images/magazine_article-pdf-42.pdf

 

[ykf7b0]

at 10-1 compression you shouldn't have a problem with the gas. i would think it is more electrical or carb. or; carry a small can of juice. i mean a 2 gal can. put a little in when you add gas. if the juice fix's it, you are running to lean. .02 cent's rick

I agree with Rick. You mentioned that you are running a Comp cam but didin't give specs. The duration at .050 would have to be massive for this cam not to bleed some compression and allow you to run even lower grade octane than 91 without pinging. I have 10.15 to 1 compression with a Mopar purple shaft that has 242 duration at .050 and have used 87 octane at times but I do try to get 93 octane. I have 915 closed chamber heads as well. I would be looking at other area's for the solution to your problem if you haven't already. You will figure it out!!

 

[Meep-Meep]

I'm running 10.1:1 440 with closed chamber heads and it will rattle on 91 if I lean on it hard. Light throttle driving is usually OK. I don't have a big cam and the engine blows 190 PSI. The correct way to get to your fuel goal is to set the compression and cylinder pressure for the octane being used while running the proper advance curve. You might take a look at your timing curve first but the other stuff like too lean, engine temp too hot, intake air temp too hot, too much advance, too much vacuum advance, large bore engine, etc.. will contribute to the condition. Get some data before making any decisions but the bottom line I think is 10:1 will not work on pump 91. If you have 906 heads and a comp gasket you're pretty much done with cheap and relatively easy mods.

 

[Meep-Meep]

......Or, I just thought of one possibility that may be cheap and easy. I just did some Mickey Mouse mathematics and you will need to add about 5 cc's to the chamber volume to drop the CR .5 point - thereabouts - and that will require you to add ~.010" to the compressed gasket thickness. Cometic makes a layered gasket but I'm not sure how thick you can go. I'm thinking 9.5:1 may get you to pump 91 but not 87. .010" shouldn't mess with the intake bolt alignment either.

 

[ykf7b0]

I love my set up because I can get by with 87 octane if I have to and I have a stout 10.15 to 1 440 engine that is .030 overbore. This engine is in a street 69 road runner with 727 and I have experimented with all gear ratio's. It is no stranger to the track with 1/8 mile e.t.'s at 7.50's and high 6.90's on nitrous oxide. Again, I have ran this on 87 octane at times. I don't know why some of you can't get by without mixing racing fuel unless the compression ratio is actually higher than thought or you have a cam selection that is not bleeding any compression at all and/or the advance is too much.

 

[hemiEssex]

Cam and timing specs

Cam Specs:
Duration at .50 227 Intake 241 exhaust
Gross Lift .486 intake .473 exhaust

Timing specs.
I sent my torque converter specs 2400 stall 3.25 gears and engine specs with the cam specs and I had a dizzy made for the motor.
It is set at:

16 degrees initial
34 total
All in at 3400
14 degrees at 10 inch vaccum
It has a vaccum advance and it is calibrated for the low vaccum.

One thing I have noticed is that the motor uses about a liter of oil every 200 or so miles. I just chalked it up to break in and was not worried. It does not smoke during start up etc. Maybe I have a leak into the intake some where that is causing detonation. No oil leaks on floor, or anywhere on engine. I am running a PCV valve on one valve cover and a breather on the other. Valve covers are un baffled. Maybe it is sucking through the PVC?? Or maybe I have a lean situation. The carb is a 670 street avenger. Jets are what came in it. Should I be givin this thing a little more fuel? Any thoughts are appreciated. I want to learn how to tune my own cars, as there is very little options for tuners around here.
Steve

 

[70rr-brian]

1 quart every 200 miles isn't good. If it were being sucked through the pcv presumably there would be smoke out the tail pipe. But if the rings never seated right and oil is getting past them one would think it would smoke as well. When you say breather....is it to atmosphere or does it connect to the air cleaner? If atmo is the engine compartment misted with oil? You should put some baffles in just to be safe. Probably wouldn't kill ya to preform a leakdown test and a compression test. Do the compression test normal the 1st time and then mist with oil the second time to see if the results improve. If they do your rings may not have seated right.

 

[lewtot184]

oil in the combustion chambers is one of detonations best friends. baffle the valve cover at the pcv.

 

[moperformance]

How bout installing a timing retard dial in the car so you can turn it back when on the gas hard? What are the cam specs? Have you done a compression check to see what you have? You should be able to run 10-1 with the right cam and tuneup and if you lower it, it will act about the same if you retard the timing. Imo, you would be better off using a timing retard on the MSD...

My box has 20 degrees of retard using the full sweep of the dial so first I set it in the middle then set my initial timing. That way I have up to 10 degrees advance and 10 degrees retard. Hope this helps.
Using a that much oil every 200 miles probably has a lot to do with your problem. Seems like one or more of the plugs would show up with carbon all over it. Good luck!

 

[Cranky]

How many miles are on the engine now? What rings did you use? Moly or cast? Moly seats real fast and standard cast takes a bit longer but should be seated fairly quickly too and that's usually within a few hundred miles. I'd have to say not having a baffle in the valve cover is the source of your oil use and ping problem.

 

[hemiEssex]

should i try

Would it hurt to disconnect the PCV, plug the hole to the intake and then put another breather in the valve cover. So I would have one on each cover. Then run it and check for oil usage and pinging? Do I need to have a PCV valve??
Thanks guys
cheers
Steve

 

[Cranky]

The engine needs to be vented and yes, you could go with a breather in each cover to check to see if oil usage drops and pinging but I would still recommend you do a compression test like mentioned above. The breathers will still put out a mist and you will be cleaning your engine compartment a lot.

 

[HEMI-ITIS]

Did you look at the spark plugs??Are they the right hear range??