Effect of a 38mm restrictor on an LS7

[stevieturbo]

Clearly you need to establish why it is using so much oil.....and given a restrictor is in place, perhaps you did not re-configure the crankcase breather system and this is why it was ingesting so much oil ?

Has it done this since day one, or is this something that has got worse over time ?

At that amount of oil, there must be some indication of where it is getting used from ?

And a 6 thou out of shape bore...sounds incredibly bad. Unbelievably bad really.

If 10thou pistons are readily available and sitting on the shelf and for standard rod size, then you are probably ok, especially as it's n/a
And if you did need a new block, there are probably better options to consider than an LS7, certainly more affordable ones.
Given the restrictor, there is probably little point in overly worrying about the size of the engine.

[C Lee Farquar]

stevieturbo said:

Clearly you need to establish why it is using so much oil.....and given a restrictor is in place, perhaps you did not re-configure the crankcase breather system and this is why it was ingesting so much oil ?

Has it done this since day one, or is this something that has got worse over time ?

At that amount of oil, there must be some indication of where it is getting used from ?

And a 6 thou out of shape bore...sounds incredibly bad. Unbelievably bad really.

If 10thou pistons are readily available and sitting on the shelf and for standard rod size, then you are probably ok, especially as it's n/a
And if you did need a new block, there are probably better options to consider than an LS7, certainly more affordable ones.
Given the restrictor, there is probably little point in overly worrying about the size of the engine.

Hi Stevie

I think the oil consumption is partly from the crankcase breather (this is connected near the restrictor) and partly the bore/ring wear. There are occasional wisps of blue smoke on some videos.

I believe the bore wear occurred just before I fitted the restrictor.

It used no oil when new.

The bore wear varies between cylinders rather than a 6 thou variation within a cylinder, The engineer who measured it couldn't be sure it will clear at 10 thou and would have preferred to go straight to 20.

I've considered other engines but if I stick with LS I need a dry sump, if I go much less power my car's too heavy to be competitive and I'd need a sequential box. I don't see any cheap solutions (other than an LS7 being far cheaper than the race engines used by other competitors).

I'm also trying to build a house so there's only so much time I have available. If I had the spare cash I'd buy another LS7 and sell my bits. But you are right, for what I'm doing you wouldn't start with an LS7.

[Boosted LS1]

Op what are your ring gaps? Your bore wear sounds huge, what are the bore measurements if you don't mind my asking?

[stevieturbo]

If your crankcase breather was connected on the engine side of the restrictor, then it would pull in huge amounts of oil.. not good.

Even on the other side, for a performance application I would never route the breathers back into the inlet are at all, unless there is very good oil/air separators to make it impossible for oil to get into the intake.

And the LS is a good platform...I just meant not necessarily an actual LS7.


Really though, first thing to do is take the block to 10thou on the worst bore and see what happens. If it cleans up, all good and well, if not, you'll need to investigate other options

[227bhp]

Markbarry1977 said:

Commented just to follow.

Max_torque you blow my mind. I swear I am a reasonably intelligent guy, all be it in electronics not engine design but I literally have no clue what your saying sometimes (no offence intended, your clearly an expert in your field). I'm now off to read about air flow and intake design so I can understand it.

Don't suppose you have a link to some appropriate reading for a novice trying to follow this. It would be greatly appreciated.

'Engine airflow' by Harold Bettes is a good place to start.

[C Lee Farquar]

Boosted LS1 said:

Op what are your ring gaps? Your bore wear sounds huge, what are the bore measurements if you don't mind my asking?

I took the block, heads off and pistons out, in before Christmas and the engineer measured the bores in the back of my Land Rover. I didn't write them down, I brought the block back to strip the rest out and am due to take it back in the new year.

I haven't measured the ring gap, I figured I'd be in for new pistons and rings anyway. The pistons are forged, a limited edition run of engines from GM, and the anti slip coating has worn.

stevieturbo said:

If your crankcase breather was connected on the engine side of the restrictor, then it would pull in huge amounts of oil.. not good.

Even on the other side, for a performance application I would never route the breathers back into the inlet are at all, unless there is very good oil/air separators to make it impossible for oil to get into the intake.

The breather fed in between the air filter and restrictor, along with the dry sump breather. The pipe was also small bore which I now realise was more likely to draw oil droplets. I didn't notice any oil in the intake when I changed some pipwork earlier in the year but there was definitely some residue when I pulled the engine.

Originally I had both breathers going to their own small filters. I changed it as I was concerned about contamination of the filters when I steam cleaned the car. I see now I must keep them separate from the intake.

[227bhp]

C Lee Farquar said:

The breather fed in between the air filter and restrictor, along with the dry sump breather. The pipe was also small bore which I now realise was more likely to draw oil droplets. I didn't notice any oil in the intake when I changed some pipwork earlier in the year but there was definitely some residue when I pulled the engine.

Originally I had both breathers going to their own small filters. I changed it as I was concerned about contamination of the filters when I steam cleaned the car. I see now I must keep them separate from the intake.

There is a third type which the OEMs use and for some reason aftermarket people rarely do, It's called a fume/oil or oil mist separator and is the most intelligent solution of the lot.
The gasses from the crankcase (sometimes cam covers too) get piped to the side of the lower half of a sealed unit, it's sometimes compartmentalised inside. It's also sometimes stuffed full of very coarse wire wool best made from SS.
When the heavily laden fumes go in the oil is seperated (by the lower temp, the wool and sometimes by a cyclone or centrifuge effect) and it drips to the bottom where it's piped off back to the sump.
At the top is another pipe, this goes to the engine intake so the engine itself draws off any pressure which can build up and burns it off.
There are pros and cons of course, but I think the advantages outweigh the disadvantages quite easily.
They go by different names and there are different types, you can pick them up for a few quid at a scrap yard.

Edited by 227bhp on Friday 30th December 08:10

[stevieturbo]

I think some BMW's have a good design oil/air separator....seen pictures but never used one

But for an aftermarket install...just make your own that will suit your install.

And presumably when you say dry sump....is this a proper dry sump, or the OEM LS7 semi dry/wet sump ?

A proper dry sump should take care of all crankcase evac with almost no requirement for additional breathers from the crankcase itself, although it will depend on the scavenge pump used.

[Mignon]

You're missing a number of important points. Unless the air filtration is non existent competition engines don't really wear bores much because they don't do enough miles. So it's more than likely you've always had whatever bore wear is present since you started using it and it ran fine for ages. Also if you're stuck with a restrictor then why bother how good the base engine is? Even if it's a bit shagged it'll be the restrictor limiting power not the engine.

So give it a quick hone, stick some new rings in, regrind the crank, check the valves and seats. She'll be right cobber.

[C Lee Farquar]

227bhp said:

There is a third type which the OEMs use and for some reason aftermarket people rarely do, It's called a fume/oil or oil mist separator and is the most intelligent solution of the lot.

Thank you, I'll look at that.

stevieturbo said:

And presumably when you say dry sump....is this a proper dry sump, or the OEM LS7 semi dry/wet sump ?

I thought I might get that Yes it's the standard sump. This main issue is clearance to a drive shaft running underneath, sub 10mm.

Mignon said:

You're missing a number of important points.

Yes, I have little knowledge of engines but I'm trying not to jump to conclusions.

Mignon said:

So it's more than likely you've always had whatever bore wear is present since you started using it and it ran fine for ages.

It was a new crate engine from GM in 2006, it's never been used in any other application. I ran a particular air intake that was useless (in hindsight) The intake manifold looked like a mud hole.

Mignon said:

So give it a quick hone, stick some new rings in, regrind the crank, check the valves and seats. She'll be right cobber.

I respect your opinion, but can I just check you're not being playful?

GM do plus 20 rings but they are for the standard cast pistons. I assume my Mahle forged ones would need different ones?

The engine works well up to 5k, as was predicated by the sages above.

[Mignon]

No I'm being serious. The engine didn't suddenly get 6 thou bore wear during one event. It just ran a crank bearing from oil starvation by the sound of it. Fix that and anything else major and the bores will still be as good as they were before. Yes your pistons need the ring pack that fits them. They'll be available easily enough.

[stevieturbo]

Mignon is right.

It's very easy to be over fussy...and he would usually be that person.

But if budget is tight, then just rebuild it on a budget. Bores dont need to be perfect, etc. I'm rebuilding mine at the minute and changing a few things....the bores have some light scores, but nothing I'll be worrying about.

A quick hone, some new rings and bearings and that's mostly it. You can easily get rings in almost any size shape you might need.
If GM dont offer them, then Total Seal will and are easy to get hold of via Dave at Performance Unlimited.

Have the crank journals checked and measured, if it needs ground, just grind it. That is an easy machine job and bearings are readily available.

Measure and inspect the pistons, if they are ok and no damage or heavy scoring, rings grooves all good and no ring sticking etc, then there may not be any real need to re-bore.

I'd like to see some actual measurements of the bores though to see how good or bad they actually are.

[Boosted LS1]

stevieturbo said:

Mignon is right.



Measure and inspect the pistons, if they are ok and no damage or heavy scoring, rings grooves all good and no ring sticking etc, then there may not be any real need to re-bore.

I'd like to see some actual measurements of the bores though to see how good or bad they actually are.

I'd also like to see if they're straight. Some aftermarket LS7 pistons come with the clearance built in. Mahle & JE do this, a .006" clearance designed into the skirt is typical. So .001" of bore wear puts them out of tolerance. I reclaimed an engine by having an additional layer of moly coating applied to the piston skirts as they to were worn.

As for the breathing aspect, your valley plate has a separater underneath. I wonder if you could put some gauze in there? It may not be a solution and no doubt others' will have opinions.

Edited by Boosted LS1 on Friday 30th December 19:48

[C Lee Farquar]

stevieturbo said:

A quick hone, some new rings and bearings and that's mostly it. You can easily get rings in almost any size shape you might need.
If GM dont offer them, then Total Seal will and are easy to get hold of via Dave at Performance Unlimited.

I spoke to the technical chap from Total Seal yesterday at Autosport, he's on the stand with Performance Unlimited.

By coincidence he has an LS7 in a drag car which he has had honed.

He passed on his experiences and I felt I would be better sending my engine up to Dave to be evaluated and honed/bored or relined there.

As I don't know what I'm doing I feel I'm better off dealing with one person who can do the engineering and has the knowledge of the parts available.

[stevieturbo]

C Lee Farquar said:

I spoke to the technical chap from Total Seal yesterday at Autosport, he's on the stand with Performance Unlimited.

By coincidence he has an LS7 in a drag car which he has had honed.

He passed on his experiences and I felt I would be better sending my engine up to Dave to be evaluated and honed/bored or relined there.

As I don't know what I'm doing I feel I'm better off dealing with one person who can do the engineering and has the knowledge of the parts available.

I didnt get a chance to speak with him myself, but Dave was on the Total Seal stand.

Dave definitely has the knowledge and abilities....but it could end up expensive.

Which again goes back to what we said earlier about how fussy one should...or should not be....relative to budget.

[PhillipM]

Steve we just piped our dry sump system to a separate breather in the header tank - it saved worrying about oil seperators and/or PCV valve systems - at least then you never really have to worry about it, just pop a plastic bag over the filter before you pressure wash it at the end of the event.

There is a good reason to stick with the LS7....one, it's already in , and two, it means you can pull full power against the restrictor for a wide rpm range given your 'box. Something small and peaky isn't going to give you that, although I suspect the unrestricted lads in the championship class are probably pushing more power than your restrictor allows...but then they're putting 40k of engine and clicky 'box in...

Edited by PhillipM on Saturday 14th January 20:49

[C Lee Farquar]

stevieturbo said:

Dave definitely has the knowledge and abilities....but it could end up expensive.

Which again goes back to what we said earlier about how fussy one should...or should not be....relative to budget.

The chap from Total Seal convinced me that honing them is not easy, you must use a torque plate and the right cutters (or whatever the term is) for honing. He said the liners are so thin that they can be stretched by the machining so it's not difficult to end up needing new liners or a block. He said that he drove to a machine shop 6 hours from his home to get the work done despite knowing of numerous engineering shops in between.

I don't have the facilities or ability to measure or the knowledge of what will work and what wont. I think it makes sense to go to someone who has the experience and knowledge of the parts available. I want to refit the engine, learn the lessons of the failures and get another 10 years use.

Thanks for your thoughts Phillip! I'm sure you're right. My car is also too heavy to be competitive with a smaller race engine, even with a clicky gearbox. A clicky gearbox on the LS would be nice is funds ever allow.

[Boosted LS1]

Honing is a simple process that barely tickles the bores. You don't need torque plates and you certainly won't disturb the liners.

The main issue is finding a garage with a honing bar of the right diameter that reaches right to the bottom of the bores. I use a firm local to me for my LS engines.

[stevieturbo]

C Lee Farquar said:

The chap from Total Seal convinced me that honing them is not easy, you must use a torque plate and the right cutters (or whatever the term is) for honing. He said the liners are so thin that they can be stretched by the machining so it's not difficult to end up needing new liners or a block. He said that he drove to a machine shop 6 hours from his home to get the work done despite knowing of numerous engineering shops in between.

I don't have the facilities or ability to measure or the knowledge of what will work and what wont. I think it makes sense to go to someone who has the experience and knowledge of the parts available. I want to refit the engine, learn the lessons of the failures and get another 10 years use.

Thanks for your thoughts Phillip! I'm sure you're right. My car is also too heavy to be competitive with a smaller race engine, even with a clicky gearbox. A clicky gearbox on the LS would be nice is funds ever allow.

Dave owns a machine shop, he can install liners so I can only presume you were not talking to him. If you are using a machine hone, then yes you could probbably need all that.

If using a ball flex hone....it will not require anything other than a drill. If the bores are as bad as you say...then no hone will fix it unless they go so far as to require new oversize pistons.

So again...it's back to how much you want to spend and how anal you want to be about it all. And whether you want to risk oversize and if the liners are really that thin.

Or a quick ball flex hone, new rings and throw it back together and save any money for a new block/build/whatever at a later date

[Mignon]

C Lee Farquar said:

The chap from Total Seal convinced me that honing them is not easy, you must use a torque plate and the right cutters (or whatever the term is) for honing. He said the liners are so thin that they can be stretched by the machining so it's not difficult to end up needing new liners or a block.

ROFL. If liners were held in a block so weakly that honing could ever disturb them they'd fall out as soon as the engine started. How TF do you think they hone them in production if it's that hard?

Utter BS.