Compression test results

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TT5.9mag said:
I run a 236/242 @050 hyd roller in a 496 BBC. It’s in a jet boat so I needed the power in the 5600 rpm range and it’s just about perfect. I’d say for a street car/burnout machine with 500ish cubes that thing should make lots of usable torque and you won’t have to twist it up all the time to do it. If you can tune it, that’ll be the key with 190 psi cranking.
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It does seem like they were going for more of a street torque machine. Maybe to over compensate for the 3.23 gears ? . .also supposedly has a 3400 stall that I have to confirm
 
Garrett Ellison said:
But yes, what issues led you to want to check compression? And well, it's not that it's usually a small cam, but it does have an intake closing of 63 degrees. Assuming you're at average altitude of 250 feet of elevation in NJ, the figures show with a 7.1 inch rod and a 4.25 inch stroke, and an average of 190 PSI cranking PSI, that if the cam is installed "straight up", you have 11.2:1 compression, on the nose. And even if it's worse case scenario of the cam having been installed four degrees advanced (I would certainly hope someone installing a cam in stroker wouldn't advance it, it's not like it's going to need any more bottom end torque with a 230 @ .050 intake duration!) it would still have 10.8:1 compression. But it can be premium pump (preferably 93 or 94 octane) compatible with efficient closed or heart shaped chambers. I've seen 11.2:1 with the same cam and similar (195) cranking pressure in a 391 stroker 318 with Edelbrock heads, and with enough tuning, it ran well on premium pump 93. What intake, cam, and carburetor will be dependent on what it weighs, and what gear, transmission, and converter, if applicable.
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Got it, I guess the next step is to check the timing. . Would a larger cam bleed off some of the compression? . . .would you agree with others that a large improvement could be had with a larger cam, good carb, & lower gears ?
 
What car is this in and what's the weight? And what kind of rear suspension and what's the tire size? If your suspension is up for 10s, you're probably looking at 4.30 or 4.56 gears and an Edelbrock Super Victor dominator flange intake (2891 for standard ports or 2893 for Max Wedge sized ports) intake with
Holley 0-8896-1 Holley 4500 Dominator Carburetors | Summit Racing
Along with this cam and springs plus any potential machine work that the .657 I/.661 E lifts that the 1.6 will produce may require.
DODGE Howards Cams 720152-08 Howards Cams Mechanical Flat Tappet Camshafts | Summit Racing
 
Garrett Ellison said:
What car is this in and what's the weight? And what kind of rear suspension and what's the tire size? If your suspension is up for 10s, you're probably looking at 4.30 or 4.56 gears and an Edelbrock Super Victor dominator flange intake (2891 for standard ports or 2893 for Max Wedge sized ports) intake with
Holley 0-8896-1 Holley 4500 Dominator Carburetors | Summit Racing
Along with this cam and springs plus any potential machine work that the .657 I/.661 E lifts that the 1.6 will produce may require.
DODGE Howards Cams 720152-08 Howards Cams Mechanical Flat Tappet Camshafts | Summit Racing
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Good info . . .it's a 72 dart, if I had to guess maybe 3200ish lbs. 489 case 8 3/4 with posi & 3.23s, stock suspension mini tubbed. I'm anticipating changing the carb, gears, suspension so I'm ok with that. Just bought hoosier quick time dot ehich are 27" in the nose. . . .would I be giving up much if I stick with a hydraulic cam for ease of maintenence?
 
My unsolicited advice is...... fix the seal and don’t go any further until you have a well defined goal for where you want the car to end up.
It’s entirely possible you might be trying to balance a level of track performance and streetability that isn’t easily achieved.

Figure out the goal, and make plans accordingly.
 
GREEN GHOST said:
The previous owner told me that some times it will start to run rough due to the valve seals in cylinder 3 needing to be replaced. After letting it sit a couple weeks I took it out yesterday and it was just not running well. Some forum members recommended I do a compression test while the plugs are out before I start on changing the seals. The plugs looked pretty trashed, all are black with varying degrees of wetness
View attachment 1715843478
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Do not change a single hard part (except plugs) until you get the tune sorted out. That thing is stupid rich. Get a good close up clear pic of a plug.
 
Yeah, definitely get the tune straightened out and then see what you’ve got. I believe you’ll need chassis work well before you need more engine.
 
TT5.9mag said:
Do not change a single hard part (except plugs) until you get the tune sorted out. That thing is stupid rich. Get a good close up clear pic of a plug.
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What seems strange is that it has an old 750dp on it which I would think might be starving it but the plugs look like this:
20211228_120305.jpg
20211228_120310.jpg
20211228_120315.jpg
 
Wow. That's horribly rich. That engine should be easy to tune. High vacuum and stock type idle. Look at carb and initial and total timing.
 
aaronk785 said:
Wow. That's horribly rich. That engine should be easy to tune. High vacuum and stock type idle. Look at carb and initial and total timing.
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Right now it actually sounds very "cammy" at idle which I like. .maybe the 750 is way jetted up or timing retarded
 
I’d start with a carb kit and overhaul, and a new set of plugs.
If the carb has the plastic floats in it, those should get replaced with brass or nitrophyl units.

Get rid of the non-projected tip race plugs too.
 
I think you have more going on with the carb then simple jetting and powervalves.
PRH said:
I’d start with a carb kit and overhaul, and a new set of plugs.

Get rid of the non-projected tip race plugs too.
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This is good advice. I’ll add check fuel pressure and float levels to it.
 
PRH said:
I’d start with a carb kit and overhaul, and a new set of plugs.

Get rid of the non-projected tip race plugs too.
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Any plug & gap you would recommend? Could they be so beat up looking from bad valve seals ?
 
GREEN GHOST said:
What seems strange is that it has an old 750dp on it which I would think might be starving it but the plugs look like this:
View attachment 1715843606 View attachment 1715843605View attachment 1715843607
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You are mis understanding how a carburetor works. A big cube engine with a (relatively) small carburetor and lots of cylinder pressure, with a (relatively) small cam will make a big strong signal at the carb. But before changing anything parts wise you need to make sure it’s functioning properly. What’s your fuel pressure at the carb inlets? Is it dripping fuel out of the booster while idling?
 
TT5.9mag said:
You are mis understanding how a carburetor works. A big cube engine with a (relatively) small carburetor and lots of cylinder pressure, with a (relatively) small cam will make a big strong signal at the carb. But before changing anything parts wise you need to make sure it’s functioning properly. What’s your fuel pressure at the carb inlets? Is it dripping fuel out of the booster while idling?
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TT5.9mag said:
You are mis understanding how a carburetor works. A big cube engine with a (relatively) small carburetor and lots of cylinder pressure, with a (relatively) small cam will make a big strong signal at the carb. But before changing anything parts wise you need to make sure it’s functioning properly. What’s your fuel pressure at the carb inlets? Is it dripping fuel out of the booster while idling?
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No gauge on it, looks to be very old and I can visibly see some fuel leaking from seals
 
Old doesn’t mean bad and conversely new doesn’t mean good. You need a fuel pressure gauge, they’re cheap and it’s another tuning tool. On a Holley you need fuel pressure to be around 7 psi. But you won’t know without a gauge. Sounds like a rebuild/freshen up is in your future. Don’t worry they’re easy to rebuild. What’s the list number? It’s on the choke horn, or on the side of the carb.
 
Pull the air cleaner off and start the engine. Look down the throat and see if it’s dripping fuel.
 
TT5.9mag said:
Old doesn’t mean bad and conversely new doesn’t mean good. You need a fuel pressure gauge, they’re cheap and it’s another tuning tool. On a Holley you need fuel pressure to be around 7 psi. But you won’t know without a gauge. Sounds like a rebuild/freshen up is in your future. Don’t worry they’re easy to rebuild. What’s the list number? It’s on the choke horn, or on the side of the carb.
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I was holding off on really adding anything to the fuel system now but seems like a pressure gauge is in order just for diagnostics. The fuel lines are 12yrs old and need to be replaced. I was going to replace tank , carb, & everything in between.
20211121_091225.jpg
 
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