Your leak down test is flawed.

My tester is 2 gauges, one is a regulator, the other is a flow through valve with a gauge. The regulator is regulating 100 psi into the cylinder and the amount of air that leaks out is measure by the open air flow valve's gauge. If you shut off the air supply, the psi will go down to 0 in a short time. You have to have a constant air source supplying at least 100 psi of air.

 

Chris you are right on the money. The more I thought about it I realize that the first one needs a regulator. I wanted to buy one like that and the guy told me I could regulate the air, but it turned out the first one just had an On/Off valve.

Thanks for the clarification all.

Another lost soul saved :lol:

 

hey, guys, i stole this off the forum for when i build one :lol:
i hope this helps some, and thanks goes out to the original poster. of course, i forget who that was :bb

 

That is my diagram ;). The second regulator is actually just a shutoff valve with a gauge though. I guess next time I should sign my work huh ;).

Chris

 

thanks for the pic, chris!

u should absolutly sign them, they might be worth $$ some day :crazy:

 

That is the one that I modeled mine after! Except the guy at A-zone screwed me with the regulators. Bastard! :lol:

 

ski_dwn_it,
Just for kicks, did a leakdown test on a engine I'm tuning for a friend. I set my supply at 100 psi, my flow through was 97 indicating 3% leakdown. Then I turned my supply up to 140psi like you were using, the flow through was 139/140 just to the left of the line! You can use the set up you have, the one I made is just a on/off valve-gauge-on/off valve-gauge-quick disconnect for hose. All you need is a regulator to put in your line. Most air compressors have a regulator on the output side to regulate the pressure in the lines used through out the shop. I've got one at the compressor, as well as one on a line that is dedicated for painting. All I do is adjust regulator at compressor to 100psi all the time, and I'm set. If you get a seperate regulator, when you are adjusting it, do it with the line out of the regulator open. What I mean is put a blow gun on your air hose, plug it in to the "out" side of regulator, and hold the blow gun on while setting your regulator. Most regulators when adjusted with "out" side closed will read less when the line is opened. As far as your headers glowing, have you tried to lower your fuel pressure or adjust your fuel mixture "leaner" at the given rpm your headers are glowing at? If not give it a try. If your headers are glowing at 3000 rpm, run your engine at 3000 rpm and either back your fuel pressure down or lean your fuel mixture at that rpm. Then let it cool back down until your headers are not red anymore, then fire it up and run it at 3000 rpm and see if they still glow. You might want to time how long it takes to glow before you start adjusting your fuel system, then once you adjust it, time how long it takes to glow again. If it is longer, you are getting somewhere, if it is quicker go the other direction with your adjustments. It is alot easier to do if you have a infared heat temp. gun. You should ask around and see if you can borrow or rent one. Do you know any guys that race circle track cars? Usually these guys(especially if they race asphalt) have them for checking thier tire temps. Just a few suggestions for you to try. Good luck :cheers:

 

You DO NOT have a real leak down tester.

For a leak-down tester to work, you must have a calibrated orifice between the inlet pressure regulator and the cylinder side. You use the pressure regulator to regulate supply pressure to make the guage read 100% leakdown while NOT connected to the cylinder, then you connect the outlet side to the cylinder and check the differential pressure across the orifice.

Anything that stops flow between the regulator and the cylinder will invalidate the test. ( IE: Your valve setup will make the result complete garbage, you have no way of calibration. )

The truth is, 10-15% STATIC LEAK DOWN IS PERFECTLY NORMAL FOR A BRAND NEW ENGINE.

What WILL cause a loss of power, on the other hand, in the order of up to 30%, or more, is too tight of a piston ring to groove up/down fit!

If compression gas can not get behind the ring, excessive blowby leakage at power will occur because the combustion pressure travelling in the ring groove clearence forces the ring to seal to the block, which is THE major contributor to putting the combustion pressure to the piston to make power.

It's something very few know about and compromises are made to adjust for it depending on engine purpose...too loose a ring groove fit and high rpm blow by occurs, too tight and power loss at all rpm's will occur. Race pistons get around it by having holes drilled into the backs of the ring grooves into the outer perimeter of the piston combustion chamber surface. That works well for racing engines that get torn down every weekend, but it only works for the first few thousand miles if these types of pistons are used in a street engine ( carbon quickly fills the holes and then insufficient ring sealing pressure occurs).

It's just another reason a blue-printed engine makes so much more power than an identical engine built to difference tolerances.



[Modified by BBA, 7:08 PM 8/23/2002]

 

BTW: I learned the above by reading a motorcycle power article back in the 80's. They were dyno testing different cams on two identical 120cc engines. pme was newly built, the other had a lot of test pulls on it. One engine made 60 HP more than the other ( on a 150 HP engine, 60 HP is a LOT to loose ), no matter which cam was in which motor. Then they started swapping parts from one motor to the other to see where the power was lost...and they found using the new engines pistons with the new piston rings in the freshly built motor was the problem, no matter which cylinder block they were in. They found that the worn out loose fitting rings in the older motor made more sealing pressure than the tight fitting new rings. At which point, they hand picked a set of rings that fit looser and got the power back in the new engine.

 

Glowing headers is from either too tight of a valve lash/preload setting, weak or insufficient valve spring pressure or some other exhaust valve closing problems, or way too RICH of a fuel mixture in the combustion chamber...and DEFINITELY NOT from piston to cylinder leakdown.

Everyone thinks too lean makes the headers glow...but thats not the case. They just don't know the physics of it.

( BTW: I'm not about to get into a pissing contest about THAT topic again. Some people just cant learn, wether you think it's me or not, leave it at that. )




[Modified by BBA, 7:24 PM 8/23/2002]

 

BBA,

Thanks for the very informational posts!

I appreciate your time in making those posts.

I agree that with the overly rich condition causing the glowing headers. However, I checked the AFR with a different scanner and the results were the same, I am running right at 14.7. I have my WB and it too says that. The two systems for checking were indepentant of one another. The ODBII scanner that our dealership has, bounced from Roch to Lean very quickly, just as it should under those conditions. Still the headers glowed. Could it just be the ceramic headers?

My RR when the valves are at their closed positions are free to be wiggled back and forth. However when I see the RR start to move ever so little they are tight as heck, unable to be wiggled. Therefore I am 99.9% sure the valves are not overtight. If they were overtight, then I would not be able to move them the way I can. If anything I am probably bordering on too loose.

I am absolutely sure that even though I was doing the leakdown test wrong. That my valves are sealing off. I applied the air at many different valve positions. When the valves were closed it sounded much different, like someone shut the air off to that particular valve. Yet the air still came from the lifter valley, which I suspect from reading is normal.

I feel it is in my better insterect to let the guys at the shop take a look. If they find the rings are in good shape, then I will tell them to adjust my valves for me, and also degree the cam. If it cost a few hundered buck, oh well.

I seriously have been working on this car nearly every other night for the past 3-4 months! I am at my wits end with it, and whatever the problem is way beyond my knowledge. Don't get me wrong, I love doing the work, but I know I have met my match.

Last night. Thinking I found the rings were leaking and that was the reason I am not running were it should was not at all bad news. I was actually relieved. I just want to get to the bottom of it.

All I want is to go to the drag strip with the car and have a good solid running machine that is capable of running mid-low 12 consistantly. Is that too much to ask? :jester

My neighbors are all very old ladies, 70s-80s. They even are asking me if I have it running yet. I think they are getting sick of hearing it running at midnight nearly every night. The one always comes over into the garage. All she says is, "It might not be fast, but it sure is shiney!"

That just what I wanted to hear after putting the time and money I have into this frigging thing. Not that I am trying to impress 80-90 yr old women with it, but give me a friggin break. :lol:

Sooner or later I will be running were I should be and baby I am gonna have a friggin party like no tomorrow! :smash:

 

One other thing I remembered...doing a leak down test, you have to loosten the rockers completely because the crank will rotate as soon as you hit air to it, which will cause one valve to open if the rockers are all tight, thereby messing up the test.

 

That is a good point. I think that Ralph mentioned that in an earlier post too. It does make sense to make every precaution possible to make an accurate test. :smash:

 

i mentioned this on the other engine post also but jim pace has L98 short blocks for $1300, i have no idea how many & doubt they will last long but a zz4 short block is a few bucks under 2 grand, other than the pistons they are basically the same thing.

 

My parents dealership's service manager found me rebuilt 350 shortblocks for the following prices. This is the place they always buy theirs from. He said they are yet to have a problem with anything. Can't for the life of me remember what the name is. If someone wants it I will call him and ask again.

Performance SB
flat top pistons
Roller chain
internally balanced
ARP bolts

8k mile warranty or 6 month
$1324.00

Stock l98 shortblock rebuilt $970.00
3 year warranty or 36k miles

If your looking to just beat the heck out of something. The stock one would probably be the one to get. I am kinda thinking about trying that out. For all the more money it is and to have the warranty, hell how could you go wrong. Do you think they could tell if nitrous was used!

 

the $1300 idea looks great, ARP bolts on the mains and rods are a VERY good idea, also the flat top piston lends it's self to high compression. great stuff...the L98 idea might be alright also but find out what they use on it first.

 

gts,

Yeah I thought they would be a pretty good bottom. Not sure how precise they are with things, but for the price its not too bad. I will see what the specs are on them Monday.

I thought the 3yr and 36000 mile warrenty would be awsome from racing. Really if you put nitrous on it, who the heck cares, besides the work involved in swapping it out, if the baby goes south. I'm sure its built as good as the stock one from the factory.

As the manager said they build a good engine. They are yet to have one come back.

I will get the details. It may be an option for some people here on a tight budget.