hacker-pschorr

Hey now, that's Mr. lunatic to you!

So far it's looking to be a very productive winter in the great white north for the Murf crew

BC

When performance developments assembled my heads, alot was done to get proper spring heights with the 944S2 springs. The S3 and S4 spring seats are way too tall to use and get proper open and closed pressures. Even cut down the S3 spring seats were too high.

Louie928

John,
The 51 lbs would have been with the S4 spring height. Using the S3 lower perches would have given higher closed pressure. In reviewing my notes, I see that I have another set of spring pressure readings and I have to conclude the readings I gave Erkka wasn't right. I have for the stock S4 springs 61 lbs closed pressure, 160 lbs open pressure at 10mm lift (GT cam). The rate would be approx 9.8 lbs per 1mm lift. Now, I don't know which is right.

Louie928

Hi Errka,
The spring pressure numbers I gave you may not be correct. I looked back over my notes and see another set of readings. Those show 61 lbs seated pressure for the intake valves with S4 springs at the stock spec height. The spring rate was 9.8 lbs per 1mm lift. That pressure is higher than my other set of notes and I can't verify which set is correct. I think the springs you are using will be fine. At the time I did my engine, I couldn't find much information on using 11mm lift cams, which springs should be used, and spring heights. I was spooked by the pits on my GT cam lobes with the stock springs and wanted to not have that happen. Were I to start from the beginning again, I'd measure the spring pressure to open the valve with the stock spring at the stock height. Then put in the new springs and set the height to give about 10 more lbs than the stock seated pressure. Maybe less increase over stock for the exhaust valves. The open pressure will be higher because of the higher lift. I also used Engine Analyzer Pro engine simulator to evaluate valve spring pressures. That requires inputting all the valve system mass; lifters full of oil, keepers, retainers, 1/2 of the spring weight, cam profile, etc. The program alerts when you have "valve toss", but also shows a top end power loss even with no valve toss shown. I tried to strike some compromise between having no top end loss and still keeping valve spring pressures within reason.

Vilhuer

As four cylinder engine springs are meant for higher lifts I think they are better option even if they weren't any stronger.

BayAreaEngineer

Thanks everyone for the helpful hints....Louis, your engineering is amazing...I remeber your GT back when at an event at devek when they were testing a MAF sensor reducer..thanks for the welcome.

Does anyone know exactly what Devek did to get those results? I have read just about everything i can find on rennlist on or by anyone who built or was going to build a stroker, but actaully, very little real test data/results. What is the blue print for a 400 rwhp engine using stock parts....how much head air flow, pistond mods, CR, cams, tuning, what is the piston to bore dims, what are the compoenent weights, crank to bearing dims, rod bearing dims, etc.

Is devek still around...Mark and Sue right? Where are they now...? How did Tim Dey get his engine built...

Merry X Mass to all.

largecar379

most of the folks doing this (strokers) are pretty much closed mouth about it.


I would offer you my suggestions, but it would not add anything due to various person's opinions as to what works.....and what can be done.

there are several avenues you can take.







--Russ

IcemanG17

Marc and Susan are still "around" just not in the 928 business anymore....

If you want to build a stroker yourself and have that type of knowledge there are guys in the bay area and on this list that can help......if your looking for a shop to drop off your 928 at then pick it up later with a completed stroker, after a large donation of $$$, then its time to call Doc Brown like others on this list have done.....

slate blue

First of all this is was posted on 928 racing, I thought I would post it here as
there might be interested readers or stroker builders that aren't members of the other website. It was an answer I gave to my original post. It starts from here.

The engine I am talking about is a 2 valve dry sump engine that will get a new custom "lightweight" dry sump with 4 stages, It also will have a teflon scraper system with windage tray. It will be a very comprehensive system indeed, I didn't post on that issue because I thought it would be just rehashing old material.

Personally I believe that our unmodified engines require in general Australian
Conditions a 20w-50 with plenty of ZDDP, for people outside Australia that would equate to weather in California. There are people on this list that have been racing with other grades of oil in Oz and ended up with no oil pressure at idle, just a mechanical tappety tap. So I personally support the thick end of the range for oils in standard engines for the reason above and also camshaft wear, ZDDP and viscosity are important factors here.

As I stated in my first post with regard to the top end of the engine the
lifters will be DLC coated and depending on the cost so will the cams. The two important things here are one my lifters are solid lifters, two the lifter/cam contact area is coated with DLC which slows wear and reduces friction dramatically. Here's a link that gives you an idea on the differences in wear

http://www.bekaert.com/bac/Products/...ne%20Parts.htm

Also I have concerns about thin oils and scuffing the rings on the bore (my top ring is barrel shaped 1mm thick, made by Total Seal) with a thin oil like 10w-30 but again there is a coating, problem is, I don't know how long it lasts, the DLC on the lifters lasts a very long time, certainly as long as the springs will last in my engine, given the springs are Comp Cams I can now afford to change them of a semi regular basis (probably check them for tension after the first 10,000 kms and again for the next 10,000) from what I have been told I would expect 100,000 kms at least. Here's the link for the piston coating, it is good reading as we use chrome rings.

http://www.poeton.co.uk/coatings-motorsport.htm

The mechanical lifters buckets are custom made in the U.K and as such I can
specify the clearance to the housing, btw they are quite cheap 14 pounds for standard lifters uncoated and 40 pounds for superfinished DLC coated ones, the reason I bring up the clearance is again if you use a thinner oil you should run a tighter clearance and this tighter clearance will also help with valve control at the high rpm this engine will see.

If you have ever seen this video on youtube http://au.youtube.com/watch?v=_REQ1P...eature=related

You will also notice how the valve stem wobbles from side to side, this shouldn't be so much of a problem on our engines as the tappet doesn't exert a side ways force. The springs I am using are beehive springs and the weight of the valvetrain weights are as follows, valve 76 grams, retainer 8 grams collets 3 grams lash cap 3 grams portion of valve spring 14 grams lifter 82 grams for a total of 186 grams intake has net lift of 0.542" or 13.77 mm. The springs have roughly 80 pounds closed pressure with 255 pounds open pressure. That compares with the stock Euro of about 290 grams and lift of 0.472" or 12 mm 60 pounds seat pressure with about 250 pounds open pressure.

The one thing that is concerning me is how to spray the springs with oil to keep them cool at high rpms. Maybe a spray bar? This is one area that some of the excess oil could be directed to.

So then we go to the bottom end, Cosworth put out a paper on their recent Grand prix engines,(the last ten years) it detailed where all the friction was in their engine, it also had a graph on the rising friction with rising engine rpm. Bottom end mechanical was roughly half the entire friction in the engine! It is in fact slightly less than half. The bottom end mechanical is made up of the mains, big ends, piston pins, piston and the rings. So the losses here are just massive, then add to that the churning losses and the pumping losses which in the Cosworth are massively better than the standard 928 engine, you
have losses exceeding half the entire friction. The pumping losses are the losses when the piston forces the atmosphere in the bottom end into the scavenge pumps and the churning losses are the oil mist/windage.

So these reasons are behind my bespoke crank which runs tighter clearances than standard so that I can run thinner oil, also in regard to the 2/6 bearing issue the crank is drilled like a Chevy with the straight shot oiling design and small teardrop, although just for the record there is now a better system that has just been devised that the top race engines are using but I wont go into that, the weakness in the standard drillings mine included are that they are said to be a great spot for the oil to leak out and lose pressure in the rods, another reason to run a tight clearance in IMHO.

My journals for the big ends are Honda sized or 48 mm or 1.888" for our American friends, the reason this size was chosen was that it was common at the time in Nascar, I run Nascar Lentz rods and if the crank needs turning down I could always go to the BMW journal of 47 mm or 1.85". Standard journals are 52 mm and the stroker cranks are the standard chevy journal of 2.10" or 53.34 mm.

The smaller big end journals are said to be worth 7 to 10 hp at high rpm also you need to consider the mass forces here too, some stroker guys have had cracked blocks, I would put this down to excessively heavy rotating assemblies and potential harmonic issues. To put this is better perspective the standard 928 crank weighs 26 kgs mine is a touch heavier at 26.7 kg from memory, the GTS crank is much heavier again. The big difference is in the bob weight, the bob weight for a standard crank is 2350 grams mine is less than 1600 grams my design for the crank was the 8 cwt design as I wanted better high rpm balance. So with lighter components and lighter oil it should spin up quite quickly.

I stayed with the standard sized mains for convenience, (I haven't verified what clearances I actually got on the mains but I did get 0.002" on the big ends.) Nascar run approximately a 50 mm journal here instead of our 70 mm, so there would be a quite a gain here, what they do is when they found gains in these areas they had the cranks made smaller and fitted inserts into the blocks, ala the chevy 2.2 whereas the latest RO7 engine has very
small mains in the block standard. No problems with longevity have been reported from race distances, the cranks are made from great material though it is a variation of 4340 and I think it is referred to as AMS 300 M although I wouldn't think it is much better than the Moldex crank material.

So add to this mix, the DLC coated piston pins I have and I am seriously
considering the ring coating. I think there is major gains here and the engine should also keep its cool as all that friction wont be there, the fuel will be turned into power not heat. The fitting of piston squirters while adding to churning losses are required to keep the piston cool as the material of the pistons is 4032 (high silicon content low expansion) like the Mahle
124S in the original 928 pistons but it doesn't like to go past 210 C.

If the oil was thinner the losses wont be as high, or I at least don't think they will. Also if I did use a 10w-30 oil I would still make sure it had plenty of ZDDP like Royal Purple. Another Nascar trick is to now use a smaller capacity oil pump (as per the early 928 engines) as a reduced amount of oil is needed with the coatings and tighter clearances, I have heard that Nascar engines are only using 50 to 60 psi oil pressure as higher pressures again rob power, so now you may be able to better understand my thinking on the total engine design, will it work for sure don't know until I try.

Greg

RKD in OKC

Don't forget that Nascar engines only have to last the race.

BC

Yes, but at redline (9000rpm) for 500 miles.

mark kibort

Marc's motor is Tim's motor . tim bought it when they took the "white car" apart. It would be interesting to find that chassis and finish it.

The 400rwhp blue print is merly the stroker that we all know and love. 6.4 liter bottomend and all stock top end except 968 intake valves and a GT cam. I did this and got 380rwhp with no real tuning yet and without the 968 valves. (optimizing fuel seems to gain 20hp or so if you are starting from the rich side, which most people start from.

mk

mark kibort

Amsoi for the oil. It has lots of zinc now in their racing oil and seems to not break down at 260F temps and high rpms!

pistons rings without chrome is recomended for the strokers using the nicasil blocks.

as far as the valve float. (that video is very interesting!) do we really need to worry about it. even at 7000rpm, the valves seem to be solid as a rock! imagine what ours look like at 5 to 6500 where we use the motor when racing!
One of the GREAT things about a 928 race car and race engine, is we dont have to worrry about the most troublesome issues in the area of the valve train. I can tell you about 10 stories of the BMW guys that twist their engines up to about 8000rpm and all the valve problems they have and have to modify to fight! We just toss in 20-25 year old valve trains and springs and off we go to the races without a care!

mk

slate blue

I wont be going to 9000 rpm, it will see 8000 rpm occasionally but 7500 is where the normal redline is planned. I am not forgetting they are race cars but I might have forgotten something else? Remember it is the principles I am copying not the engines, their engines run on 0w-7 oils, I am not going that thin or using oil pressure that low, it is a modification coming from technology that wasn't around at the time. Just look at the Chevy LS7 engine as a example of a production engine that uses later tech in an old design. I understand why you make the point though.


Mark I am hearing you on Amsoil, you can't really buy it here, Royal Purple is more common and very expensive but in the case for the gearbox it was certainly worth it.

As to the revs, well I reduced the stroke of my crank, the reason is, once the engine is built, my engine just uses domestic "wear"parts, such as pistons, pins, valves and springs, most parts will never need replacing, like the rods, just for the sake of story Lentz told me that some people use them in 1000 to 1200 hp engines that spin to 10,000 rpm, He said you won't hurt them. As I was doing a 2V stroker, things are a bit different as I can't use 968 pistons and here in Australia there is nobody doing the Nicasil either.

So the build is different, also in another thread, stroker guys said they wished they could use 103 mm pistons, well my 103.124 mm pistons are off the shelf items for my engine at Mahle Motorsports. $800 for the set coated for Alusil, I wasn't that keen on the side thrust that is exerted in a normal stroker with a piston with short skirts like a GT3 piston, my rod to stroke is the same as a GT3 btw.

Then when I had the cams ground, they didn't tell me that it was a solid grind but really it didn't matter, I needed the biggest bump stick I could get, it is also a fairly quick cam but still is supposed to have street reliability, solids are the way to go again the springs are cheap. Now to your comment about the BMW guys having trouble I would be interested in hearing what you have to say here. Are they early engines? The M3 sixes, don't they redline around 7,500 rpm? The new engines use some very light bits, some are common to the GT3 engine, GT3 engines have very little trouble, is it just a BMW thing like their brakes?

Last word on the revs, I didn't want to break my drive line, so I went with the theory of more revs and less torque, longer spacing between gear changes, my car already has trouble getting of the line with a 5.0 litre euro.

Greg

IcemanG17

Its out there and i'm sure they would sell it......its pretty well gutted with just the body-cage & maybe fuel cell left?