Compression and leak down tests
Thread Starter
Joined: Jan 2002
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From: Casselberry FL
Compression and leak down tests Looking for some hands-on help performing these tests to confirm I have no problems in the shortblock which might be causing me to be down on power. Casselberry area, PM me please.
Thanks!
Thanks!
Thread Starter
Joined: Jan 2002
Posts: 4,069
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From: Casselberry FL
Shortblock's been in the car since, hmm, last June I want to say. Some are claiming I'm down a good 40+rwhp *shrug* scr should be around 11.4, dcr around 8.9. See here:
https://ls1tech.com/forums/generatio...92-intake.html
When I didn't gain anything from the Fast 92 makes me think something is amiss.
https://ls1tech.com/forums/generatio...92-intake.html
When I didn't gain anything from the Fast 92 makes me think something is amiss.
Thread Starter
Joined: Jan 2002
Posts: 4,069
Likes: 74
From: Casselberry FL
I'm near the intersection of Red Bug Lake Road and SR436. How long does this process take? Do we do it dry first, then confirm with a wet test? Is it a good idea to follow this up with a leak down test?
I ordered the cam through Mike Norris, and he also built the shortblock. I requested he degree the cam and I don't have any reason to believe he didn't.
I ordered the cam through Mike Norris, and he also built the shortblock. I requested he degree the cam and I don't have any reason to believe he didn't.
Try this...disassemble the FAST intake, then bolt up just the lower of the three sections to the engine( you may need some shorter bolts without the upper housing installed) to see what the port alignment looks like. Since the deck height of this engine is considerably shorter than stock considering the block being cut, the heads being cut, and the thinner head gasket, It's fairly likely that the intake ports are not aligned with the head ports and it (intake)may need a little epoxy/port work to work correctly.
Thread Starter
Joined: Jan 2002
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From: Casselberry FL
That's something which has been in the back of my mind regarding the original installation. I doubt they take the time to check this, although it would be nice to merely be told they are out of alignment and offer to fix it there. I bet I would find it does need massaging, but I'd be skeered to handle the epoxy/port work myself.
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will start with a compression test. and go from there, if we find problems then we can check it with leak down test. we can also check the intake alignment if you want. ill be free sunday afternoon i think.
if it needs work, i recommend whistler ive seen his epoxy port work first hand its amazing.
if it needs work, i recommend whistler ive seen his epoxy port work first hand its amazing.
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Chris brings up a very viable point for sure in verifying that the intake ports line up correctly.
The only other time I have seen a FAST not do much at all if on a set of poorly flowing heads. And keep in mind that a head may have good number with an open port, but two heads with the same CFM on an open port can have quite drastically different numbers with the intake bolted on.
If need be Jimmy we can do the leak and compression test here and on a weekend if need be. Let me know if the other offers pan out or not.
Mike Norris
The only other time I have seen a FAST not do much at all if on a set of poorly flowing heads. And keep in mind that a head may have good number with an open port, but two heads with the same CFM on an open port can have quite drastically different numbers with the intake bolted on.
If need be Jimmy we can do the leak and compression test here and on a weekend if need be. Let me know if the other offers pan out or not.
Mike Norris
Thread Starter
Joined: Jan 2002
Posts: 4,069
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From: Casselberry FL
I know Lizzy flowed two intake & two exhaust ports at our request last summer, but I know he didn't have the intake and I don't recall if he had an exhaust pipe. But either way I don't think it was flowed in the optimal method.
Weekends seem to be best because the car is outside and poor lighting to work under the hood weekday evenings.
It appears that the FAST needs some TLC during re-assembly regarding preventing leaks, etc?
92slowmaro: I'm PM'ing you my cell number.
Weekends seem to be best because the car is outside and poor lighting to work under the hood weekday evenings.
It appears that the FAST needs some TLC during re-assembly regarding preventing leaks, etc?
92slowmaro: I'm PM'ing you my cell number.
Thread Starter
Joined: Jan 2002
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From: Casselberry FL
I drove the car around 10:30AM running some errands, then it sat until 2PM. Ryan with the compression gauge was to be here at 2PM so I wanted to get a head start on getting things disassembled. I had almost started pulling spark plugs when he called to advise he was on his way, and he requested I run the car for just 20s before pulling the rest of it apart.
Cylinders 1,2,7,8: 160
Cylinders 3,4,5: 165
Cylinder 6: 170
That was with turning the engine over ~3 times. Whistler thought with the SCR of 11.4 that it should reach a higher number, so we re-tested #1 turning over ~6 times, and that yielded between 195-200. I inferred there was a question on why it didn't build more compression sooner.
The port alignment between the intake and the heads was off about 2/16" of an inch on the floor of intake port 1. Intake gaskets are red, which I presume are the FAST gaskets.
Cylinders 1,2,7,8: 160
Cylinders 3,4,5: 165
Cylinder 6: 170
That was with turning the engine over ~3 times. Whistler thought with the SCR of 11.4 that it should reach a higher number, so we re-tested #1 turning over ~6 times, and that yielded between 195-200. I inferred there was a question on why it didn't build more compression sooner.
The port alignment between the intake and the heads was off about 2/16" of an inch on the floor of intake port 1. Intake gaskets are red, which I presume are the FAST gaskets.
Last edited by JimMueller; Apr 19, 2009 at 06:19 PM.
I usually crank them for 5 to 6 compression strokes to get a reading. 195-200 is not bad with that cam. Did you do a leak test also??
You mention that the port alignment is off 2/16" (1/8") whihc is a bit, but as long as the step is getting bigger going to the head not a big deal. Now if the port on the intake is larger then the port on the head creating a step up, then there can be a bad flow issue even at 1/8".
Mike Norris
You mention that the port alignment is off 2/16" (1/8") whihc is a bit, but as long as the step is getting bigger going to the head not a big deal. Now if the port on the intake is larger then the port on the head creating a step up, then there can be a bad flow issue even at 1/8".
Mike Norris
Last edited by Mike Norris; Apr 20, 2009 at 06:09 AM.
Thread Starter
Joined: Jan 2002
Posts: 4,069
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From: Casselberry FL
No leak test, didn't have an air compressor. The intake port sits down about 1/8" lower than the floor of the head intake port (creating a step up). Whether that's significant I do not know.
Having that step up is not helping and a step that large could cause quite a disruption in airflow. Is the exit of the intake manifold larger then the cylinder head port all the way around??
Mike Norris
Mike Norris
Thread Starter
Joined: Jan 2002
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From: Casselberry FL
No, we couldn't see the edge of the roof on the head intake port. I don't know how much lower the intake port ceiling is than the head port ceiling, we didn't try to scribe a mark, etc.
Thread Starter
Joined: Jan 2002
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From: Casselberry FL
The idle is surging more since we put everything back together. Not sure if that points to a resolved issue where the tuning simply needs to be adjusted or a new issue.
Thread Starter
Joined: Jan 2002
Posts: 4,069
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From: Casselberry FL
All of the throttle body bolts could easily be snugged 1/2-1 full turn but the intake bolts themselves were all snug. That seems to have cured the surging problem. At least until I was tuning the VE in 4th gear through 6800RPM a few times on SR429 and when I pulled into a parking lot to change the calibration it was overshooting a bit. But under normal conditions it seems at least very similar to before.
