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Effect of a 38mm restrictor on an LS7

Effect of a 38mm restrictor on an LS7

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Discussion

C Lee Farquar

Original Poster:

1,843 posts

137 months

Monday 16th January
quotequote all
I may have misunderstood what he was saying to me. This was to increase the bore by 10 thou from standard. He mentioned something about a diamond cutter.

I'm taking the block, crank and pistons to be measured at Performance Unlimited next week. That should put me in a better position to decide what I can get away with.

Boosted LS1

16,340 posts

181 months

Monday 16th January
quotequote all
.010" is rebore territory plus new pistons, rings plus a balance job of the crank. It's the worst case scenario. I suspect you only have .001" of wear in which case the bores just need a tickle with a hone. That's the best case scenario and massively cheaper. You could use file fit rings to restore nice tight ring gaps.

Still, lets see what measurements you get. :-)

stevieturbo

12,581 posts

168 months

Monday 16th January
quotequote all
Usually for the smaller engines, you can get pistons in 5 thou oversize which you could regard as a hone or bore.

Clearly a DIY hone is never going to take 5 thou out though....well unless you're very patient. So this would require a proper hone tool. And DIY tools would never guarantee a proper parallel bore etc.

Whether 5 thou is enough to clean yours up...again to be determined. Whether it is all worth it.....value for money etc etc...to be determined.

Whether just to chuck it back together at very modest cost....there can be a lot to be said for that too.

Boosted LS1

16,340 posts

181 months

Monday 16th January
quotequote all
Op said:

"I want to refit the engine, learn the lessons of the failures and get another 10 years use".

You won't get that from an ls7 used for competition. They are good blocks/engines but I'd never buy an ex comp engine. It'll be buggered.

Stan Weiss

210 posts

69 months

Saturday 21st January
quotequote all
Max_Torque said:
Right:

1) do the regulation specify the position of the restrictor, and crucially, the geometery of the pipework upstream and downstream? if not, hurray, you can quite get a lot of air through a 38mm hole and with proper geo and get a decent pressure recovery downstream. Normally, the position is mandated to prevent people installing inlet systems that can help negate the restrictors pressure loss! (i.e in WRC, it has to be <50mm from the turbo compressor eye etc)

2) Make sure you feed the restrictor with the highest pressure air availible to you! A 38mm smooth edges restrictor will choke (the point at which the flow through it becomes just critical (supersonic) at 0.270kg/s (assuming 1bar, 15deg C upstream) and at this point the air pressure in the choke will be 52.8kPa (abs). At the critical point the downstream air (and shockwave) can no long propgate up stream (as the flow is now supersonic) so no matter how much you reduce the downstream presure you can only flow 0.270kg/s! But, increase the upstream airpressure, and the density increase will increase the mass flow. So gain say 5kPa (for 105kPa (abs) from dynamic ram in your airbox at high vehicle speed and you get 0.284kg/s ;-)

3) we know the conditions at the choke must be critical (52.8kPa (abs) and Mach1.0) so we need to slow the air back down in as efficient a manner as possible, "recovering" the dynamic pressure back to static pressure with as little loss as possible. This takes a expansion nozzle with an included angle something less that 15deg. Generally by limiting where you can put the restrictor, the regs aim to make it impossible to install a nice pressure recovery nozzle, and it can be difficult to get discharge co-efficients >90% in these cases.

4) a 7.0litre engine, sucking in air at 15degC, with 95% Man Vol Eff, and an inlet manifold pressure of 95kPa will be consuming that same 0.270kg/s we can flow through the restrictor at only 4275rpm. As engine speed rises above this point the plenum pressure will be throttled by the restrictor, and effectively WOT (Wide Open Throttle) will not actually be WOT ;-(
As a double whammy the engines overall pressure ratio will fall as rpm rises resulting in an increase of in-cylinder exhaust gas residuals as the charge scavanging efficiency falls, this will result in a higher end-gas temperature and may lead to detonation phenomina, requiring spark retard (and resulting in even less power output that directly as a result of the reduced airflow)



So what we need:

1) the best intake system & restrictor geometery possible:
- nice long straight, even and slowly tapering pipe downstream of the restrictor to the throttle.
- High static pressure upstream of the restrictor (smooth, large diamter, intake, with a MASSIVE entry diameter bellmouth feading into the smoothest precisely 37.999999999999999999999999mm dia hole you can make
- use the vehicles speed to increase upstream restrictor pressure above ambient

2) An engine that is as efficent at using air as possible
- high static compression ratio
- good detonation resistance
- Valve timing optimised to prevent charge contamination on the overlap
- makes peak power at as low rpm as possible to reduce Fmax (engine mech friction)
- has as low exhaust backpressure as possible (reduce effect of engine pressure ratio falling)
- lowest parastic friction as possible (lowest oil pump, water pump, camtrain & ancilary loads etc

I suggest a good long look at other race series restricted engines to see what has been done to optimise the powertrain for the restrictor!!
I must have missed this the first time around.

Since I do all my calculations in American units I had to keep going back and is what I had not converted or used correctly. But I get the kg/s very close.

My problem is either I got my cfm wrong or I am wrong in my calculation of velocity as I only come up with 684 fps.

Does anyone see what I am doing wrong?

Stan


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C Lee Farquar

Original Poster:

1,843 posts

137 months

Sunday 22nd January
quotequote all
Hi Stan.

I can't help with the math, but the restrictor size was increased to 42mm in 2014.

I calculated, hopefully correctly, that this gave a 30% bigger orifice.

I would be interested to see how this affects the other figures calculated.

Stan Weiss

210 posts

69 months

Sunday 22nd January
quotequote all
C Lee Farquar said:
Hi Stan.

I can't help with the math, but the restrictor size was increased to 42mm in 2014.

I calculated, hopefully correctly, that this gave a 30% bigger orifice.

I would be interested to see how this affects the other figures calculated.
Since I am still waiting to see if my calculations were correct. Please takes these knowing that.

Stan


Stan Weiss

210 posts

69 months

Monday 23rd January
quotequote all
Was the engine when fitted with either the 38 mm or 42 mm ever dynoed?

Stan

C Lee Farquar

Original Poster:

1,843 posts

137 months

Monday 23rd January
quotequote all
Hi Stan, thank you for your time.

It has never been dynoed. I bought in new in 2006 with an E38 ecu. Initially I ran without a restrictor.

I did one race with the 38mm restrictor, quite a few with the 42mm.

Once I get the engine sorted I plan to get the ecu better set up for the restrictor.

C Lee Farquar

Original Poster:

1,843 posts

137 months

Saturday 28th January
quotequote all
Update for anyone who's interested.

I took the block to Dave and he's taken the worst cylinder out to +10 thou and he feels it needs another 7 thou to take the lip out. From most sources +5 is the recommended max oversize although +10 has been done successfully.

I took the crank to be crack tested and it is significantly cracked and scrap.

My current thinking is to try and sell as is and buy a new one when I've saved some money. I think the cost or liners or a block, crank, pistons, rings, couple of con rods, bearings etc. will be too high.


stevieturbo

12,581 posts

168 months

Saturday 28th January
quotequote all
C Lee Farquar said:
Update for anyone who's interested.

I took the block to Dave and he's taken the worst cylinder out to +10 thou and he feels it needs another 7 thou to take the lip out. From most sources +5 is the recommended max oversize although +10 has been done successfully.

I took the crank to be crack tested and it is significantly cracked and scrap.

My current thinking is to try and sell as is and buy a new one when I've saved some money. I think the cost or liners or a block, crank, pistons, rings, couple of con rods, bearings etc. will be too high.
A new short motor would be the best option. Or simply a replacement short motor....foregoing the LS7 aspect.

Although without the long nose crank you will probably lose the "dry sump" aspect of that particular engine...not that it seems to have worked very well in this instance.

eg

http://www.thompsonmotorsports.net/product_info.ph...

Or literally just go and find a good used LS2 or whatever and throw it in and enjoy it and think about any potential upgrades after that

C Lee Farquar

Original Poster:

1,843 posts

137 months

Saturday 28th January
quotequote all
Thanks, I have been looking at short engines but I think they will work out more expensive. Assuming it would be £5k landed.

There seems to be differences of opinion as to whether the LS7 heads will fit an LS3 block. TBH, the compatibility of bits concerns me, I don't have much knowledge, most advice is contradictory. I'm building an unusual house without detailed plans, I'm finding this challenging enough without learning how to be an LS expert.

The LS7 sump has worked perfectly, the oil light never came on when it had enough oil in the tank. The consumption caught me out, a gallon in 200 miles. The other reason I need the sump is clearance, I have a propshaft running about 10mm under the sump and block. I could possibly have a custom sump made to saddle the shaft but I still have to deal with surge. Time consuming and expensive, and if the oil pick up needs modifying even more hassle.

Then I have the loom and ecu to sort out, gaskets, new bolts.

Finally, the engine wasn't running right before I spun the shells and I'm not sure why. With a new engine with new injectors and sensors I would hope the problem would be cured or at least easier to solve.

Also, an LS7 comes run in which is handy for a car you don't want to drive on the road.


stevieturbo

12,581 posts

168 months

Saturday 28th January
quotequote all
The fitment issue is only due to the valve sizes intended for the larger bore engine, so any shortblock using a 4.125" bore, your heads will fit just fine.
On a budget boring out an iron block might be the easiest way to achieve that, although some iron blocks apparently have shorter bores so not ideal for 4" strokers as per a 427/7.0L

And yes I'd say US $5k will easily be UK £5k landed, perhaps a bit more given exchange rates are crap at the minute.

But you could find a good used LS engine of various capacities in the UK for around £2-3k. Perhaps less to throw into the car and use. Although you'd need one with a 58x crank trigger and 4x cam wheel

Most later engines have the 58x crank and if you had to change a camwheel it wouldnt be the end of the world. Cheap and easy to replace.
So you could have a complete engine to swap fairly easily. Just not sure if you could work with the shorter crank and the LS7 oiling system

ERL could do a setup with proper bores and to suit your heads ( either 427 or 454 ) but at a higher price. And you'd need to purchase a core block to start from, cheapest are the 5.3 blocks and apparently strongest anyway, so add another $850 or so. I'd assume they could do you a crank with the longer nose too.

http://www.erlperformance.com/product/erl-na-stree...

It will just be more expensive to stay with the 7.0 platform vs moving to a smaller engine

If you could adapt a sump to use, and stick with a normal engine...even a brand new crate in the UK isnt terribly expensive for a complete engine

http://www.partsworldperformance.com/ls3-v8-crate-...

C Lee Farquar

Original Poster:

1,843 posts

137 months

Sunday 29th January
quotequote all
If it would fit I'd have an LS3 over a new LS7 and save £4k less ecu and loom costs.



the problem with fitment is that the valve covers only just fit in the inverted v of the roll cage. The hand made ali transmission tunnel also fits snugly. I really can't lift the engine.

I've had to grind the bottom of the block to clear the propshaft that runs to the rear diff. It's possible to lower the centre bearing of propshaft a little but then I lose my flat floor and it's running out of line.

This shot is looking forwards. The shaft runs 10mm below the transmission sump and about the same below the starter ring.

An aftermarket dry sump would be OK but I don't like belt driven oil pumps for off road work.



ERL stuff looks good, core charges kill it though.

stevieturbo

12,581 posts

168 months

Sunday 29th January
quotequote all
There is no difference in external dimensions of an LS7 vs any of the other LS platforms, other than the varying accessory drives.

So if an LS7 fits...the LS3 can fit.

The cheapest core charge is for the alloy 5.3 at around $850...not terrible for a brand new block. And for any built short motor you opted for, you'd just buy an LS7 type crank with the longer nose.

Maybe something like this would leave room in the middle for a shaft LOL


http://gmauthority.com/blog/2013/07/crazy-australi...


But you could easily have any short motor built with the crankshaft with the longer nose. If you opted for this and say an LS2/3 block it would bring the overall price down vs an actual LS7 based engine.

C Lee Farquar

Original Poster:

1,843 posts

137 months

Sunday 29th January
quotequote all
I raced against an interesting V16

here


stevieturbo

12,581 posts

168 months

Monday 30th January
quotequote all
C Lee Farquar said:
I raced against an interesting V16

here
Yea, I think someone posted about some of that mad stuff a few years ago. It's cool to see people doing stuff like that !

AW111

3,621 posts

54 months

Tuesday 31st January
quotequote all
C Lee Farquar said:
I raced against an interesting V16

here
Here is a longer compilation of the v16 (2 1/2 mins). Some of the stages it sounds like a giant electric RC car.

PhillipM

5,172 posts

110 months

Thursday 9th February
quotequote all
So, when's the Jag engine conversion then?
I hear there's a load going cheap...hehe

C Lee Farquar

Original Poster:

1,843 posts

137 months

Friday 10th February
quotequote all
PhillipM said:
So, when's the Jag engine conversion then?
I hear there's a load going cheap...hehe
Wouldn't be the first time! I expect you remember all those new supercharged engines at £2k a decade ago?

Been having off thread conversations considering the options.

My current preference is to sell mine on ebay as a complete lump for someone else to fix and buy a new one. Then buy a new one. Mrs CLF seems to think a new (house) roof is more urgent.

Considering building to a smaller capacity so we can run lighter in France but I don't think the weight lose will make up for the loss in power.

Work and house build is quite mentally draining at the moment. I rather like the idea of saving up and getting a direct replacement. Plug and play in a day. Not too bothered if I don't race until October.