marvin
Oh, yeah,... .015" preload is what I set all the Quattro engines with stock brgs to that I build at our dealership here.
Ken.[/QUOTE]
Wow, that's .381mm, do the crank even turn by hand!
griff851
Well yesterday i squeezed in a full 8hrs. First I began on the the heads. I fitted the new valve guide seals, then went for the smallest closing shim, exhaust first then Inlet. Much to my disgust the cam fouled the rocker arm on both. Nuts! This is what I get for losing my piece of paper, with the figures on it before sending the valve seats to be machined, and buying a set of valves for $50, that looked like they might fit. So I fitted the openers and took all the measurements. Monday its off to the valve seat machining guy and get the valves dropped 0.3-0.4mm for the exhaust and 0.4-0.5 for the Inlets, that will give a whole 1.1mm to play with on the closers. Its probably a good thing as the Inlets valves were sitting a bit proud into chamber.
The next drama was the con rod bearing. After having the journal polished it was time to recheck the clearance. One rod is 0.050ish mm with 998 red shells and the other is 0.07ish with 998 blue shells. I swapped rod positions and got similar results. Dam! It does go to show that the bearing manufacturing tolerances come into play, and that the machine shop failed to carry out my instructions correctly. Poofters! luckily I think I can now move into the monster range of shell. Mondays job.
Griff
griff851
Today after staring at the crank in the vice, and having coffee and smoke, trying to make a little more sense of the dilemma. I decided to get the DTI out and measure the shells. While looking for a steel flat plate I discovered a secret stash of 998 blue shells hiding under a fallen wall chart. I measured them all and found all to be 1.492 maybe 1.493 tops. So I grabbed two sets and threw them in the rods and broke out the flexi gauge. This time it made more sence. Just under the 0.050 mark on one rod, and just over if not dam close to bang on 0.050 on the other. The temp this morning was more normal at about 26-27°C as opposed to the 36-38°C the other day.
Still at the wrong end of the tolerance, I decided to ring up the coating guy. Yep, he has a special bearing coating that a light coat constitutes about or just under 0.0005" (Ford and GM guys still speak imperial here). This will take me down to the lower tolerance of 0.025mm. I think I'll go with that.
Griff
WolfManSpecial
hello,sorry but dont understud your last movement🙁
griff851
Sorry, it should be DDI not DTI. Basically the conrod BE/Journal tolerance is 0.025mm-0.059. Ideally I would like 0.032-0.038mm. The available bearing shells will only let me have one end or the other of the tolerance range. If I leave the shells as they are its the top end of the range, if I coat them with a ceramic coating I go to the tight end of the range. If you go too small there is a risk of not enough gap for an effect layer of oil. If you go too big the rod will flop about on the journal and you add a vibration which will lead to accelerated wear. Its not that much of an issue at 0.050 (still with in the range), but at least if the coating wears off, and eventually it will, the tolerance will still be in range.
Griff
griff851
Today the heads are at the valve seat cutting blokes shop, he has managed to convince me that 30° back cut is a crock, and that 39° gets better flow. Has anyone any arguments against before he starts to hack into them? Other than the one that the manufacturer uses 30° and they generally know what they are doing.
Bearing shells are being coated which will give me near on the lower tolerance. However, using scotch brite I can get my 0.032-4m if I'm anal enough.
Griff
griff851
Correction first. Its a change from the seat top cut 30° to 39° this article explains it better than I can as before I read it I knew nothing. Now I know a little bit more than nothing. A 30° back cut on the valve itself is a good thing.
http://www.enginebuildermag.com/Article/16025/the_inside_angle_on_valve_seats_what_you_need_to_know_to_go_with_the_flow.aspx
Attached is a pic. The top green band is being changed to 39°. The seat contact will be 46. And I don't know what the the third angel will be at this stage, let along whether he is adding a fourth. I will call Todd on Monday and get the gen on "Race Cut"
Griff
griff851
I've finally pulled apart my 748 throttle bodies and they are now prepared for boring out. Unfortunately first I have to fix the lathe. I ordered the bit so now I have to wait.
Having some sort of known sizes (thanks Robert), 748 43.5mm, 851 46mm, and 996 50mm. I have come to the conclusion that for every 18.5cc you go up, you need another 1 mm of bore size at the bottom of the throttle bodies. So at 888 I need 47mm or just a tad more due to the port cleaning up and valve seat changes. It has to be remembered that this is street application, a race eng is open season. The next issue is to straight bore or taper. Bob tapered his 54mm butterfly, 52mm lwr bore,(for a 1026cc) but found that by changing the size of the angled step down he lost throttle response. Anyone else experienced this?
I also rang up Todd the eng builder guy and the valve seats will be 39.45.58 intake and 45 mm seat/valve face and radius's on the others for exhaust. An approx increase of 15-20 cfm and a few extra HP as previously proven on a Dyno. So it seems you may want to consider this if your doing head work.
Griff
brad black
the 888, 916 and 996 throttle body outlet size is exactly the same, tapering down from the 50mm throtle to 46.5mm from memory. i thought the 851 were the same as that too.
griff851
Hi Brad, Yes I thought that all the bodies were the same, but somebody at the shop mentioned that the 996 was restricted for road use, and they should have had a 54mm butterfly with 50mm hole. Anyway when I put this theory to Todd, he seemed to think that was about right.
Griff
griff851
I might ring up Arthur and Pete Smith and see what they have to say.
Griff
hauge
griff851 wroteI've finally pulled apart my 748 throttle bodies and they are now prepared for boring out. Unfortunately first I have to fix the lathe. I ordered the bit so now I have to wait.
Having some sort of known sizes (thanks Robert), 748 43.5mm, 851 46mm, and 996 50mm. I have come to the conclusion that for every 18.5cc you go up, you need another 1 mm of bore size at the bottom of the throttle bodies. So at 888 I need 47mm or just a tad more due to the port cleaning up and valve seat changes. It has to be remembered that this is street application, a race eng is open season. The next issue is to straight bore or taper. Bob tapered his 54mm butterfly, 52mm lwr bore,(for a 1026cc) but found that by changing the size of the angled step down he lost throttle response. Anyone else experienced this?
I also rang up Todd the eng builder guy and the valve seats will be 39.45.58 intake and 45 mm seat/valve face and radius's on the others for exhaust. An approx increase of 15-20 cfm and a few extra HP as previously proven on a Dyno. So it seems you may want to consider this if your doing head work.
Griff
Gidday!
I´m also interested in the tb thoughts. I have double sets from a 996 for my 1026 project. I´m still thinking of either taking a set out to 48 mm and standard butterflyes or making 54 butterflyes (54mm) tapering down to 50mm.
I´m NOT interested in losing throttle response just to get some more top end.
Edit: missed a quite importan word above.....
Cheers
Thomas
griff851
Right, I just got off the phone to Pete Smith. As big as you can go without cutting into the air bleed gallery.Which is line with the "race open season" comment. He has gone to 60mm at the butterfly plate section and 54mm I think he said on the out let with out any problems on a 916. Any transition problems you take out with mapping, to keep throttle response good. The big cruncher is the inlet manifold, you have to take that out to close to your TB outlet diameter. Which is what i suspected as you are trying to build a gentle taper tube before the ports. He confirmed don't hack out the ports too much as your trying to keep air mass velocity, not flow. Try to get close to 86-87% port to valve ratio. So I have a choice. 996 inlet manifolds which are 49mm, or go to 47-48mm outlets depending on how much I can remove from the 851 inlet manifolds. My Manifolds are on my heads at Todd's so I'll get them back and have a look. It the old adage still, "got to get them flowing to get them going"!
Griff
marvin
Why are you trying to build a high RPM engine, do you have a stash of rocker arms that you wanna destroy? ! 😁
griff851
It like a Ferrari, you don't have to use the power, but its nice to have it there. But yes, just in case I do have a stash of rocker arms. 😁 Actually I'm with Steve on the feeling that anything over 10,000 rpm and you just wasting away crank case life.
Griff
marvin
griff851 wroteIt like a Ferrari, you don't have to use the power, but its nice to have it there. But yes, just in case I do have a stash of rocker arms. 😁 Actually I'm with Steve on the feeling that anything over 10,000 rpm and you just wasting away crank case life.
Griff
Unfortunately most of the "things you do" to make for high end power makes for a real "dog" anywhere else.
griff851
A very valid comment. Yep its a trade off. I generally herb around town at 5 grand, don't drag race off from the lights and blast through mountains between 6 and 8 ish, but thats where the old eng felt good. I guess you adjust your riding to where it feels good. With a close ratio gear box it shouldn't be that much of a drama, and if it is, I guess I'll get another set of heads and start again.
Griff
PS Its just that i can't help myself, I read something and say well while I'm here I might as well, just to see what happens. I haven't changed the ports where they split by any great amount, virtually nothing. So it won't in theory be all that much of a high rpm motor.
brad black
you'll find bigger throttle bodies make them more responsive because you have to open the throttle less to get the same air in so for lower throttle openings you get the same performance. so it feels better at the twist grip. aprilia used 51mm then 57mm on the rsv motors, and i think honda used 60mm on the sp1/rc51. all the journos called them responsive, except those who couldn't open a throttle smoothly.
i think the aprilia guys find going from 51mm to 57mm beneficial over 135 or so dynojet hp, altho capacity increases will also cloud that.
i don't think velocity thru the throttle body has a great deal to do with it at all, especially at part throttle when the blade is a disturbing restriction anyway.
if you're running short duration cams and big valves like a 998 motor then the throttle body size may be a factor to power output to do required air flow over a shorter time window. but i've put 54mm ones on ported 996sps and seen no difference.
griff851
Ok then, so the its a bit like the increase in velocity stack case, in that it does SFA at low to mid range and only really makes a slight to minor increase in HP at high rpm. Where of coarse the torque curve has already dropped off.
What about torque?
I am only trying to get this right in my head, but. If you increase the length of the intake manifold, there by increasing the mass of air charge, which has inertia, you are forcing more volume of air into the cylinder during the valves time open. Hopefully increasing dynamic cylinder pressure and getting more torque. Then widening the inlet track area is not as effective because you have decreased the velocity of the air charge ( The pressure would have increased due to the wider area). Until of coarse you get to high rpm when the mass/volume/inertia thing starts to work properly again.
So if you manage to increase the available flow rate at the valve (by port work or increasing the cc of the cylinder) then naturally you should get an increase in velocity of the charge. If you widen the intake track, you slow the air down and loose what you have just tried to gain.
In which case leaving the Tb's at 46-46.5 or whatever is advisable, as ducati have already worked this out.(Funny about that!)
This of coarse changes at some point when a larger cc engine requires more flow, than velocity, as discussed in that porting school web site stuff.
Hows that sound?
Griff
got2dv8
ok my question is this...why use 50mm on one end and 44/46mm on the other? Seriously...is this just because of production ease? Can someone verify 916/996 tb size as i've read 44mm which is the same as 748..and smaller than 851/888.
Robert
