[leeklm]

Not looking to start a filter debate- but I was curious about the function of oil filters with an internal bypass or relief valve.

Like many here with race applications, I have plugged the factory bypass on the oem filter adapter and ran various filters like the Fram HP4 and a Bosh extended life filter (or similar) that has a high burst strength rating.

The HP4 includes an internal bypass, along with a screen filter to keep out any big chunks going through the bypass. My question... if the filter relief valve is rated at say 22lbs, and the system psi operating at 60psi, does this mean a large percentage of oil is going through the bypass, or does the bypass only come into play when the filter media is plugged or cannot keep up with the volume?

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[Sirrotica]

It comes into play at pressure differentials. When the pressure side is 60 psi and the clean oil side is 40 psi then a 20 lb relief would open allowing equalization to both sides of the media being 60 psi, once equalized to under 20 lbs differential, it will be closed.

Any filter will experience a pressure drop when the fluid crosses through the media, when the differential is too much, is when internally lubricated parts will starve for oil.

Blocking a relief will hydraulically place an inordinate amount of pressure on the media, and then it can collapse, or rupture. When that happens all the solids caught previously in the media will be pushed directly into the bearings. I've never blocked a relief on any of my street, or race engines because of the potential of a catastrophic media rupture, dumping the whole contents of the filter downstream. Other people will disagree, but a conventional oil filter was never designed to operate without a by pass valve, and the media area is too small to filter all the oil, all the time.

Smokey Yunick calculated it would take 4, 1 foot long filter cannisters to filter 100% of the oil of a engine at full RPM. Just look at how much filter area you have in a conventional filter, compared to 4 feet of canister at full RPM. With a conventional oil filter you're about 44 inches short of media, from Smokey's calculations.

[spectramitch]

When running a stock housing with a functional bypass, should you use a filter with no internal bypass? or does it not make a difference?

[Sirrotica]

Not all oil filters have internal bypass valves. The correct Pontiac filters don't have bypass valves internally, it would be redundant to have two. The designers of the Stratostreak V8 opted for an in engine bypass valve.

If the filters had an internal bypass valve, blocking the one in the filter elbow would have no effect.

Many GM engines have bypass valve located in the engine, and no need for a valve in the filter. The filter media in a conventional filter is not fine enough to remove all the finest particulate, which causes most engine wear, when it becomes concentrated to a high percentage, due most times to extended oil change intervals.

[chuckies76ta]

Not looking to start a filter debate- but I was curious about the function of oil filters with an internal bypass or relief valve. Well, my way of looking at it is, the bypass in the filter tells me that if there is pressure differential at some point, the bypass will open and flow oil to the engine. I too like Sirrotica, have never plugged the bypass on the filter housing. Reason for me is so the engine may never be starved of oil. I would have to say it was engineered like that for a reason. I don't run a bypass filter. I would also agree with Sirrotica that two bypass are redundant, but I would rather have two then none.

[Jay S]

Most oil filter’s with an internal bypass the bypass pressure is 8 to 15lbs. 22 is comparatively really high, depending on the flow rating, that is fine IMHO. I can’t remember what Pontiac bypass pressure was, 8 at the most I think. 50+ year old factory bypass spring probably is lower. When I have had trouble it is pretty obvious the factory type is constantly bypassing, a few lbs difference on a bypass can make a big difference. I plug the factory and run a higher bypass’s in the filter. But it depends what filter is available too. Some I leave factory. It doesn’t bother me to not run a bypass if the filter has a high enough rating, then change filters so they stay fresh, especially over here in the race section. Filters should have rating specs listed if you look up the specs, that flow rating is not utilizing the bypass.

[Sirrotica]

The original HO bypass valve modification was engineered to replace one bypass valve with another. The HO modification didn't totally eliminate the bypass valve, it removed one, and substituted another one in the Lee 2 stage filter.

I was around making my living as a mechanic, and working on my race cars at that time, so I have first hand information on the modification. Lee went out of business in a matter of years after the modification was featured in the car magazines at the time.

To my knowledge The original HO bypass modification was to be used with a Lee 2 stage filter which did have a bypass valve built into it, and when it opened, it filtered oil through a second section that only the Lee filter had. The modification was not to be used with a single stage filter with no bypass valve, the blocked bypass valve was eliminated, but then replaced by a specially designed filter with an internal valve. People that had the modification usually couldn't reverse it easily because the elbow would need replacing, so I guess they just started using single stage filters without a by pass valve, and some people thought it was a good idea.

If I had never seen a filter with crushed/ruptured media, I might draw that conclusion also, but this was also the time period when the 80 PSI SD pumps were available from Pontiac, and they did make standard oil filters of that time leak when the oil was cold. I had one in my 428 in my 69 GP, and even if it was idling cold, the O ring would leak, and the 100 PSI gauge would be pegged, until the oil warmed up and thinned out. As I already posted, my engines had the bypass valve operating, and they still leaked when the oil was cold, not zero degrees either, this was in the mid thirties, right around freezing.

I've also looked into filters and seen the media flattened down, crushed, and in one case it was actually torn, so all the dirt that was caught, got released into the engine. In all instances the bypass valve was operational, but the hydraulic pressure still damaged the filter media internally. Seeing this first hand cured me of ever wanting to block the bypass valves in any engine, especially my own. The blocking of the bypass to my knowledge, and it's pretty extensive, especially with performance cars, and engines, has never saved any engine from destruction when something went awry mechanically anyway, so I see no reason to block it. They will still destroy bearings, even with blocked bypass valves.

If a needle bearing in a roller lifter grinds up, are you just going to throw a new filter on it after changing the defective part, and run it? I highly doubt it, because even if the bypass is inoperative, there is going to be shrapnel all through the engine.

In the 428 in my GP I blew a hole through the piston, there was aluminum in ever nook and cranny of that engine, all new bearings, hot tank and rifle brushes to get it all out before rebuilding. A blocked bypass valve wouldn't have saved anything, because the oil was so hot that it wasn't opening the bypass valve, excessive heat is what caused the piston to melt initially. Brand new filter, and brand new oil, first time out after building the engine. So much for an oil filter stopping metal particulate from circulating. I didn't even make 1 lap after the piston melted through.

A real race engine many times has an Oberg tattle tale oil filter, which is basically a fine screen in a canister that catches errant particulate. It is used not so much to clean the oil, but as an engine health indicator. Periodically it is inspected and cleaned, to show what type of solids are in the oil, much the same as reading plugs tell the fuel mixture needs corrected. Certain solids will tell a skilled mechanic what is wearing, and if it needs immediate attention.

If you study the video, you'll notice the flat screen in the Oberg filter, and how it lends itself to showing metal particulate much better than dissecting a pleated conventional oil filter. Even though the Oberg filter is a performance style filter, it does include a bypass valve in it for situations that oil flow would be restricted to the engine internals. If a performance company has designed a bypass valve into their filters, I'm certain that they have weighed out the benefit, risk factor of not having a bypass valve.

If you have a good PM program for your engine, you're certainly changing oil, and filter often enough that a blocked by pass valve is of no real benefit.

Link to inspecting an Oberg oil filter:
https://www.youtube.com/watch?v=gShCgKrGgPU&t=466s

This has been my own experiences with performance engines, and oiling systems. You can choose to ignore all of the information if you so choose to.

[Dragncar]

K&P offers a Pontiac oil filter with or without a by pass. There is so little pressure drop with them that even with a by pass version there is little chance of it ever by passing.
They are cleanable, reusable and you can buy new screens for them. They spin on your stock adapter.
Plug your by pass in your PMD oil filter adapter and run their filter with a by pass, done.

https://kandpengineering.com/product/S16/

[Jay S]

Originally Posted by spectramitch

When running a stock housing with a functional bypass, should you use a filter with no internal bypass? or does it not make a difference?

If you did use a filter with a built in bypass, and internal Pontiac bypass, the bypass that has the lower pressure setting will always open first. The higher pressure bypass will never open.

Ideally the filter should be able to filter the full flow of the oil when hot and not run on the bypass. If the bypass opens and there is a particulate that gets by the bypass it gets to run thru the system over and over until the filter media blocks it. If it is a catastrophic failure and the filtration is overwhelmed the fanciest filter set up probably won’t help a lot. The damage is done. But, when possible, it is always a great idea to clean that particulate out after one pass thru the filter system.

Trying to catch particles in one pass, or for increased efficiency, things like that are why we block the bypass sometimes, or add secondary bypass filter systems. Some filter systems get the oil cleaner than it was when the oil was new and first put in the engine. All the filter systems work at some level of efficiency, Pontiac’s factory system included. If the factory bypass spring is getting weak, the efficiency of the filtration is lowered, because there is more oil thru the bypass circuit, and some particulates will take more passes thru the system to get caught.

I don’t find it to necessary to get bent out of shape one way or another on filters. My Grandpa bought a plain 283 power 61 chevy that didn’t even a place on the block too have a factory oil filter. The oil filter was the screen on the oil pump pickup! LOL

Good info on the HO system!

[Sirrotica]

Just for grins, a little Lee Maxifilter trivia. I found an old 1983 TV commercial on You Tube for the Lee Maxifilter, 2 stage oil filter. It has a small animated schematic on how the bypass valve works, even though it's in bypass mode, the oil that is detoured around the main filter, still gets filtered by a second filter. This is how the HO modification was intended to work, by substituting one bypass valve for another. Problem was that Lee Maxifilter was discontinued, leaving those people that had made the modification, without a filter source. To my knowledge, no other oil filter was made the same as the Lee Maxifilter was, before, or since.

https://www.youtube.com/watch?v=Z9DAp4DXsQY

Lee was owned by Champion Labs, same company that still produces many private label filters, among some of the better known labels is Bosch, Supertech, K&N, Mobil1, and STP.

As far as I can determine, the Lee portion of the business was shut down sometime in the 90s. Lee was never a huge name in filters, and had limited availability through retail outlets, and the availability dwindled as time went on. I was surprised that it stuck around into the 90s, because I hadn't seen any Lee filters in retail outlets since the late 70s, early 80s.

[nas t eh]

The way I see it there are a few options.

1. Stock short Pontiac filter with factory unfiltered 8 psi bypass.
2. Stock long Pontiac filter with factory unfiltered 8 psi bypass.
3. High Performance Pontiac/Buick/Olds/Cadillac filter (available short and long) with factory unfiltered 8 psi bypass. (eg Fram HP 5 - short or Fram HP 2 long)
4. High Performance Chevy filter (available short and long) with screened internal 22psi bypass and factory unfiltered bypass blocked off. (eg. Fram HP4 - long)
5. Remote mount filter plate( factory bypass eliminated) on the block and dual remote filter housing with High Performance Ford filters with screened internal 22psi bypasses. (eg Fram HP 1 - long)

I like options 4 and 5 the best, even if options 1-3 are good enough.
Fram HP 4 or HP 1 filters are low cost.