Why is it so hard to get good advice !!???

-
Kern Dog

Kern Dog

Build your car to handle.
FABO Gold Member
Joined
May 23, 2010
Messages
9,752
Reaction score
28,074
Location
Granite Bay CA
It seems that everywhere I turn, I get conflicting advice.
I'm trying to get the 493 to run right on pump gas. It currently has 10.7 compression with aluminum heads and the cranking compression is between 210-220. The cam is the MP 292/509. I have a 727 with a 9 3/4" converter and 3.91 gears.
The general consensus on the various web forums is that this engine CAN be street friendly with the right cam. Everyone so far agrees that the cam I have is too mild for the engine size and it traps too much cylinder pressure. Time after time I have read that I need a bigger cam, or more accurately, a cam with a later intake closing event.
I want the car to run strong on 91 octane fuel without detonation. I want power and reliability. I may drag race it some day, but 99% of the use will be spirited street fun.
I bought some 1.6 rocker arms to increase my lift from 509 to 543. Of course this means new/different pushrods. As I was getting ready to measure them, I wondered if I should just go ahead and change camshafts. One cam that looks interesting is the Comp Cams 294H. It has 250/256 degrees I&E Duration @ .050, ..553/.558 lift with the 1.6 rocker arms. This gets me within the .600 limits of the springs in the heads. I spoke with a guy at Mancini racing and he liked the cam, but he also liked the idea of using a thicker head gasket to lower the compression. This makes the THIRD time a "tech" guy on the phone has suggested a thicker head gasket. EVERYONE else online thinks that the thicker head gaskets would reduce the quench effect and make the engine MORE likely to detonate. I was slow to catch on but I am now thinking that the theory of quench may have merit.
 
quench is where its at. What pistons are you using? above deck, below deck?
 
Is this a running motor? If so.. What is it running like ? Is it detonating?
What seems to be the problem ?
 
Use online calculators and see where your DCR is. Get it under 8:1 and it will run on pump gas all day on the hottest day.
 
Rod-length on a 493" stroker is 'usually' the same as a stock 440-length. 6.7xx" thereabouts I recall.

I'm having a somewhat similar problem my own Eddy headed 493".
I went from a stockish hydraulic cam with 1.6 rockers, to a solid roller cam with 1.5 rockers. (1.5 rockers to stay below the .600 lift range of the springs).
The roller cam is the CompCams XR274R-10.

Now the engine pings after it gets warmed up (under the hood), mainly because that cam creates more cylinder pressure.
It doesn't ping when it cold so I'm fairly sure the pinging also has it's origin in the hot air being drawn into the motor.

Creating a cold air intake is something I would strongly advice looking into at first for your problem. Also try keeping the engine-temps low enough by using a 160 T-stat for instance.
 
EVERYONE else online thinks that the thicker head gaskets would reduce the quench effect and make the engine MORE likely to detonate. I was slow to catch on but I am now thinking that the theory of quench may have merit.


What is the quench now? If you arent in the proper range then quench dont mean much.. Increasing the lift i don't think will do much its the overlap/duration that bleeds off pressure. Maybe you have gotten good advice but are looking for an easy way out? Start out by getting to know you motor all the specs then go from there
 
I put the straight up 292/509-108 cam spec in my dyno program and it said its a 58 degrees intake closing point at 0.50", B rod length 6.358 and RB rod lenght 6.769.
Is your engine based on 440 or 400, 440 would have the RB lenght but 400 could have either.
 
RustyRatRod said:
Use online calculators and see where your DCR is. Get it under 8:1 and it will run on pump gas all day on the hottest day.
Click to expand...


Okay, Using the info provided by "273", I came up with 8.99 dynamic and 10.73 actual. With this I'll be able to calculate what #s I'll have with another cam.
Thanks all!
**********************************************************************************************
UPDATE :
Holy crap! I JUST looked up the cam specs for this Comp cam I was looking at. It has an intake closing at 73 degrees ABDC! That cam would make my dynamic 7.99! Wow...I might have stumbled onto a cure here (With the guidance of some great guys)
Thanks again!
 
mbaird said:
Is this a running motor? If so.. What is it running like ? Is it detonating?
What seems to be the problem ?
Click to expand...

I'm sorry if I wasn't clear before. I have posted about this problem in a few forums so I have forgotten what I mentioned.
The engine has about 2500 miles on it since Feb 2011 when I had it out to deglaze the cylinders and put in new rings and bearings.

The engine makes decent power. It idles okay and has no hiccups or stumbling. Its just that I cannot run more than 31 degrees total timing without hearing detonation. Anything past 1/2 throttle and I'll get pinging. I have the distributor set to 17 degrees initial, 31 total and NO vacuum advance. MP electronic distributor and a Chrome box ECU. I can get the car to full throttle without pinging if I use some 110 octane race fuel, but to me that seems like a cop out. I want it to run on pump premium without detonation. Limiting the timing seems like I am cheating myself out of power. The way the car ran, I just KNEW that the combination was mismatched and that there was MORE power to be found. The 292/509 cam was picked by me because in 2004 when I first assembled the engine, Mopar Performance has a crate 500 engine that also used the '509 cam. I thought I was making a safe choice. I later learned that the MP engine was built on 9.5 compression and the '509 cam worked well with it. My higher static compression ratio is obviously not right for that cam.
Learning the cranking compression numbers and now the Dynamic ratio have really cleared things up. Sometimes it takes cold, hard facts to get me to understand.
 
1970Duster said:
quench is where its at. What pistons are you using? above deck, below deck?
Click to expand...

The pistons are flat tops, sitting .017 in the hole with a .039 head gasket. This puts me at the edge of quench with the .056 number.
 
Frankenduster said:
The pistons are flat tops, sitting .017 in the hole with a .039 head gasket. This puts me at the edge of quench with the .056 number.
Click to expand...
I`d try a .020 head gasket, put you about .036 , would be about optimum ( and minumim) for steel rods. it would help a lot! I`ve got .038 :coffee2:- .039 on my 505 w/ 7.1 steel rods. just my 2 cents-----bob
 
at .056" you have NO quench so if a thicker head gasket or a real thick custom one will lower the CR enough to get the DCR to an acceptable level then dont let the quench situation stop you since it's a non issue here. I been following your situation. Holler how it goes
 
famous bob said:
I`d try a .020 head gasket, put you about .036 , would be about optimum ( and minumim) for steel rods. it would help a lot! I`ve got .038 :coffee2:- .039 on my 505 w/ 7.1 steel rods. just my 2 cents-----bob
Click to expand...


I agree but would go with a .027" MLS gasket if your going to spin it over 6000 rpm just to be safe.
 
If you have .056 now you do not have any real quench now. The engine should have been built with dished pistons to get quench and higher static. So - you can drop the compression via gaskets too, but IMO that's a mistake. You found out the dynamic is too high. Because the quench is not there I would lower the dynamic to below 8:1. It will make more power overall with the larger cam, so don;t sweat it. Just change the cam.
 
Looking at the specs I've seen elsewhere, some list an intake closing point @ .050, others leave the .050 part out. THAT makes comparisons difficult.
In post #9 here, member 273 listed the 292'509 cam as having an intake closing at 58 Degrees ATDC. A guy on FBBO showed some link that showed the '509 to have a intake closing at 74 degrees! AHHhhhhhhh!!! The Comp cam I liked showed an Intake closing at 73. This stuff is so confusing!
 
Have you tried colder plugs? I had pinging pretty bad and went 2 steps colder, cut it in half. My engine is 10.2 with iron heads and I can drive it now because of the plugs.
 
Just remember, 90% of advice is to benefit the person giving it to you. Not the other way around. :D
 
72BBSwinger said:
Have you tried colder plugs? I had pinging pretty bad and went 2 steps colder, cut it in half. My engine is 10.2 with iron heads and I can drive it now because of the plugs.
Click to expand...


Edelbrock calls for Champion RC12YC plugs. Those made the engine run on and on... even after shutdown. I wanted to try RC10s, but I had trouble getting them. I've ran RC9YCs and they stopped the dieseling completely.
I didn't notice a difference in engine performance or spark knock.
 
moper said:
If you have .056 now you do not have any real quench now. Because the quench is not there I would lower the dynamic to below 8:1. It will make more power overall with the larger cam, so don;t sweat it. Just change the cam.
Click to expand...

Wouldn't there be some quench even at this number?
I have talked to people at Hensley Performance, Comp cams, Mancini Racing and all of them have offered advice opposite to what I have read on several web forums. This is what they had to say:

Hensley: "You need a thicker head gasket to lower the compression and a smaller camshaft."
Comp Cams: "The '509 cam should be just fine. I wouldn't change it. You just need a thicker head gasket to lower the compression."
Mancini: " A thicker head gasket, something like a Cometic MLS would lower the compression enough to run on 91 octane. I'd do that along with using the 1.6 ratio rocker arms to give your cam more lift."
See what I am dealing with?
For the record, even with my lack of experience, I agree with the following:
Quench helps an engine make more power by allowing it to run more static compression without detonation.
An engine with over 190 cranking compression will not run to its potential on 91 octane fuel.
Long stroke, big displacement engines can tolerate a more radical cam than a stock stroke 383/400/440.
In 2006 I tried the combination of a .060 Cometic head gasket and a Comp XE285HL cam. The car ran great but I never drove it hard enough to determine the detonation condition. It wiped a lobe within a few weeks. I tried another cam and it also failed. I felt burned by what I thought was defective Comp cams products, so I reinstalled the MP '509 with new lifters.
 
why cant you back up the initial timing and bring in the advance curve later???? its a big block they don't like all that timing.... just sayin
 
In my program I put the advertise and the 0.050" duration the .509 lift and 108 and installed straight up. The program gave advertise and 0.050" intake closing points 58 was at 0.050" which the CR calculator needs plus 15 so 73 and I'm sure it was 70 something at advertise. I don't know how the computer program gets its numbers but I'm sure there in the ballpark. Plus if you advanced or retarted the cam that's gonna change the intake closing number.
 
The cam is installed straight up, which was shown to be 1.5 degrees retarded when we degreed it.

Years ago when I first built the engine, I actually had it advanced 4 degrees. The cranking compression was in the 230 range then!
 
In terms of quench - the smaller the disance the greater the benefit - it's the parts getting very close that squishes the mixture to the plug. That's what "quench" is. Keeping the intake charge mixed and inducing what they call "tumble" and "swirl". that process cools the outer regions of the chamber lessening the tendency for the liquid fuel that falls out of suspension and ends up out in the dead spots to self-ignite. The further apart the parts are, the less squish. The less squish, the less affect. You get a lot of benefit when the distance is less than .035. I tend to run between .025-.035 depending on the rod, the bore, and the commpression height of the piston. You get less affect from .035 there to .045. You get almost nothing over .050. The best example is to take your hands and bring them together in a prayer looking pose - a clap with your hands near enough to your face to feel the air movement. Clap once. Then stop your hands when they are an inch apart. then 2 inches. What does that do to the air movement you feel on your face?

You are asking a lot of builders, a few manufacturer, and hobbyists for opinons on a fix. If you cast a big enough net you'll catch one of everything and there are many ways to skin this cat... none are right or wrong. they will all help with your problem if done properly. You can slow and limit the timing curve. You can replace the ehad gaskets to lower the static and dynamic ratios. Or you can change the camshaft to lower the dynamic. In my opinion the best way is the camshaft approach. the cheapest would be head gaskets and change the timing - but to me you're giving up on power by keeping the small cam and hobbling the engine to run with it.
 
You must log in or register to reply here.
-

Back
Top