vbares Vittorio Bares Mega Moderator Location: Londonderry, NH Join Date: 04/10/2007 Age: Ancient Posts: 413 Rally Car: Audi 4k (3b conversion) |
Last event - we had some challenges (blew up a turbo and cooked the motor) - so the opportunity presented itself to build it better than it was
Subject: 2.2L 5pot Audi motor w/20v turbo head J&E Rods Weisco 81.5mm flat top pistons coated bearings Balanced rotating assembly 3-angle on the head light skim guides and seals CC'd the head - looks like we're at 9.48:1 CR - I wanted to get to 10:1 due to the 34mm restrictor on the turbo. Restrictor will limit flow to ~29 lb/in - so we're looking to produce torque at the bottom end and give up hp at the top (basically limited to a theoretical 290chp) - we saw 240whp on the dyno with a GTX2862 @3400 rpm with stock pistons and stock CR (9.3:1). I have a guy looking into a custom turbine starting from a GT2871 - from what I've read/studied having close to zero trim on the turbine wheel should allow quicker spool at lower rpm and thereby more torque at the low end, giving up top end...which is restricted anyway. But, I digress - that said, I'm looking for the vast wisdom on this forum with regards to cams... It has been suggested that if I were to use 7a cams and advance the timing on both exhaust and intake I could pop more exhaust into the turbine, thereby getting boost sooner as well as suck more fuel/air into the chamber - oh yeah, and I'd like to run pump gas... I found this nifty piece of data in the pic below... Many Audi folk will add the 7A exhaust cam for high end power enhancement - I'm not convinced with my application, restrictor and goals this is the best way to go - but I am thinking that using the stock 3B cams and adjustable cam gears could give some benefit in the low end without compromising my restricted power limit on the top - what say you? |
vbares Vittorio Bares Mega Moderator Location: Londonderry, NH Join Date: 04/10/2007 Age: Ancient Posts: 413 Rally Car: Audi 4k (3b conversion) |
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Cosworth Paulinho Ferreira Ultra Moderator Location: Charlotte, NC Join Date: 03/15/2007 Age: Midlife Crisis Posts: 721 Rally Car: Honda Civic |
Make sure you dont thin out the gasket too much and get the quench pad too tight, the piston to head clearance should stay around 1mm (40 thou) |
Do It Sidewayz Chris Martin Professional Moderator Location: Toronto, Ontario Join Date: 01/15/2006 Age: Midlife Crisis Posts: 567 Rally Car: E-85 powered Impreza |
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john vanlandingham John Vanlandingham Elite Moderator Location: Ford Asylum, Sleezattle, WA Join Date: 12/20/2005 Age: Fossilized Posts: 14,152 Rally Car: Saab 96 V4 |
Sounds like a broad hint... do you think you could hint just a little more why he should not? All in hinty hint type tone...You can tell us, we won't tell anybody.... all as hint naturally John Vanlandingham Sleezattle, WA, USA Vive le Prole-le-ralliat www.rallyrace.net/jvab CALL +1 206 431-9696 Remember! Pacific Standard Time is 3 hours behind Eastern Standard Time. |
Do It Sidewayz Chris Martin Professional Moderator Location: Toronto, Ontario Join Date: 01/15/2006 Age: Midlife Crisis Posts: 567 Rally Car: E-85 powered Impreza |
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john vanlandingham John Vanlandingham Elite Moderator Location: Ford Asylum, Sleezattle, WA Join Date: 12/20/2005 Age: Fossilized Posts: 14,152 Rally Car: Saab 96 V4 |
Since we have ample evidence that with enough money spent the restrictor doesn't slow anybody down---except the poorer privateers----and we see other bigger countries going to larger restrictors for the National cars ----why would Canada be doing something in the opposite direction than these other countries with more and longer experience? Look at the way Australia has adopted the idea of choice: people can choose either full FIA Group N rules to the T including FIA spec fuel--and 32mm soda straw or they can choose no restrictor and run on pump gas.....and its working fine...and it seems about 3/4 have chose the smarter choice: pump gas and no restrictor.. Shirley Canada can learn for others and craft something that serves the majority and saves huge amounts of money. Presuming CARS gives a shit about the well being of their series--because when the Aussie foolish went to straight GpN and 32mm their series suffered a huge loss of entries and interest.. John Vanlandingham Sleezattle, WA, USA Vive le Prole-le-ralliat www.rallyrace.net/jvab CALL +1 206 431-9696 Remember! Pacific Standard Time is 3 hours behind Eastern Standard Time. |
Cosworth Paulinho Ferreira Ultra Moderator Location: Charlotte, NC Join Date: 03/15/2007 Age: Midlife Crisis Posts: 721 Rally Car: Honda Civic |
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john vanlandingham John Vanlandingham Elite Moderator Location: Ford Asylum, Sleezattle, WA Join Date: 12/20/2005 Age: Fossilized Posts: 14,152 Rally Car: Saab 96 V4 |
then wtf is anybody yammering about 32 for? Seems a number of places allow 36mm for National cars... The rationalizing that USA and or Canada should adopt FIA spec for anything is truely stupid when nobody is dragging the club spec Blue Subie to rallies in Portogallo or Italy or Bulgaria... THEY, those especially in smaller (geographically/population) countries might want to do some events in other countries just casue their own country might no have so many rallies or the level is low so some kind of common spec is understandable...But "we" don't even speak with our cousins to the South so its just USA and Canada.. Its sooooooooooooooooooooooooooooo stupide have now 2 decades showing restrictors only hurt low budget teams. John Vanlandingham Sleezattle, WA, USA Vive le Prole-le-ralliat www.rallyrace.net/jvab CALL +1 206 431-9696 Remember! Pacific Standard Time is 3 hours behind Eastern Standard Time. |
vbares Vittorio Bares Mega Moderator Location: Londonderry, NH Join Date: 04/10/2007 Age: Ancient Posts: 413 Rally Car: Audi 4k (3b conversion) |
Well you're both right (I'd rather see pump gas as the only allowed fuel) - now with fluctuating restrictor requirements one would want to build for flexibility.
Lets review - money spent on optimizing for restrictor so far in the motor: uhm zero... I've also decided to leave the HG alone as the 0.5 CR gain really isn't worth the effort, dollars or potential reliability. On the cams - Audi made several motors with the same bottom end but different heads. The cams in two of the motors ares described in the chart above. The 7A is a 20v NA head and the 3B is a 20v turbo head. 7A has cams that have a longer duration (not sure about lift) and start a bit earlier than the 3B - These cams can be acquired for a couple hundred bucks. If we add another couple hundred bucks for adjustable cams - would it make sense to: a) Go with the 7A cams and longer duration b) index the cams for more advance to improve spool My thought is that this could provide for a very flexible platform that can be adjusted for different intake limiting rules. (if we could stay focused on the technical merits of this approach it would be appreciated ) |
Cosworth Paulinho Ferreira Ultra Moderator Location: Charlotte, NC Join Date: 03/15/2007 Age: Midlife Crisis Posts: 721 Rally Car: Honda Civic |
Vitorio, more duration and lift isnt particularly preferable on a restrictor car. It tends to raise the powerband in the rev range and decreases port velocity. So on the exhaust it will hurt spool up in the lower rpms. Also it will effectively decrease your dynamic compression ratio. I'm sure those stock cams are still small enough not to hurt the performance but I'm sure John will know more about this. |
vbares Vittorio Bares Mega Moderator Location: Londonderry, NH Join Date: 04/10/2007 Age: Ancient Posts: 413 Rally Car: Audi 4k (3b conversion) |
I'm not at all knowledgeable in the dynamics of engine speed and what happens as you approach TDC - but I would imagine both valves would want to stay closed for as long as possible during the compression stroke to get as much bang as possible. Given that, I don't see how the suggesiont of advancing cam timing, opening the exhaust early would be good...??? Just trying to understand the dynamics and inform my choice - this is good - thank you! |
Pete Pete Remner Ultra Moderator Location: Cleveland, Ohio Join Date: 01/11/2006 Age: Midlife Crisis Posts: 2,022 |
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aj_johnson A.J. Johnson Ultra Moderator Location: Pendleton OR Join Date: 01/07/2011 Age: Settling Down Posts: 1,381 Rally Car: 88 Audi 80 |
Some missing info_
170HP( 7A ): In open before TDC 6 In close after BDC 38 Ex open before BDC 42 Ex close before TDC 3 Lift intake=10,5mm and lift ex=10,5mm S2/S4/S6(AAN/ABY): In open before TDC 3degrees In close after BDC 25 Ex open before BDC 42 Ex close before TDC 9 Lift intake=9,5mm and lift ex=8,6mm |
Josh Wimpey Josh Wimpey Junior Moderator Location: VA Join Date: 12/27/2006 Age: Midlife Crisis Posts: 649 Rally Car: Sneak the Golf |
I run a GT2871 setup on my street car (1995 S6 Avant with the 2.2L 20v 5-cyl) and it is no spool monster. I get about 5-6psi at 3000rpm even in 4th and 5th gear and about 26psi by 3700RPM. Not sure how much of this is a tuning problem (off the shelf 034 tune for the GT2871) but I have tried running a manual boost controller in lieu of the N75 valve and it made little difference in spool rate. Of course, I know nearly nothing about turbo setups and this is the first car I have ever owned with one. Not sure it is helpful but below is my current setup---no restrictor. If you have similar performance, it would be pretty awful with a restrictor.
Details: Wagner HO RS2-style exhuast manifold Stock cams 0.5mm oversized exhaust valves 3" downpipe and exhaust with hi-flow cat GT2871 (obviously with kkk flange) AR .63 ____________________________________________________________- One. Class -- 2WD www.quantumrallysport.com http://www.facebook.com/home.php?#/pages/Quantum-Rally-Sport/281129179600?ref=nf |