Alex Posted January 20, 2002 Share Posted January 20, 2002 These things make no sense to me but are probably really useful in determining what turbo is best for you. So can anyone please explain these in laymen's terms? http://www.turboneticsinc.com/comp_maps/fig10.html Quote Link to comment Share on other sites More sharing options...
Chris Wilson Posted January 20, 2002 Share Posted January 20, 2002 Quote: from Alex Holdroyd on 10:07 pm on Jan. 20, 2002[br]These things make no sense to me but are probably really useful in determining what turbo is best for you. So can anyone please explain these in laymen's terms? http://www.turboneticsinc.com/comp_maps/fig10.html Not had time to SPECIFICALLY look at thes maps, but in general terms a compressor map shows the air flow at certain pressure ratios of the turbo, over RPM of the turbo. To make use of them you need a good idea of the engines appetite for air at given RPMS, which can be worked out from its adiabatic efficiency. To say it's a complex subject that few get the experience needed to grasp beyond the theoretical stage is an understatement. I got into long discourse with Geoff kershaw, MD of Turbo technics many years ago re a Volvo engine I was building to run turnboed. I spent hours with calculators and maps, suggested a turbo spec (T)4B is S4 trim) to him and he said "No, that may look OK from the maps, but a blah blah unit will be better". i said but, but but the maps suggest it's too small. He said 25 years with turbos told HIM otherwise, and to hell with the maps. he was DEAD right... Like many mathematical and computational assessments of the internal combustion engine, they get you close, real world experience gets you closer. I have just done the same with my RX-7 turbo, I got close, gurus in Oz suggested something similar but slightly less restrictive on the exhaust A/R. They will undoubtebly be correct. Experience... You need to get a turbo that is running in the centre "islands" which are a percetage efficiency area. What people are doing with stock TT turbos is running them faster, up top right of the maps, overspeeding them and well outside their optimal efficiency. Temps go up, reliability comes down. Exhaust back pressure goes sky high, combustion and valve temps rise, det occurs and a big bill is the result if taken to extremes. Move to turbos that have the airflow requirements at a sensible turbo RPM, and efficiency area on the map and things improve, but they are usually laggier. Quote Link to comment Share on other sites More sharing options...
Alex Posted January 21, 2002 Author Share Posted January 21, 2002 So are you saying if you find the T-66 at high boost can get you the power you want go for the T-70 or whatever to bring it down to a lower boost pressure for the same power...add the lag but think of the longer lifespan. And try to resist the urge to add that extra boost! Would you then try to reduce lag with over fueling (flames out the back job, from a motec ecu) or nitrous? Would you just put up with it? Would porting the head (especially the exhaust valves) and having 264i & 272e cams reduce the lag and help the spool up. Cheers Chris - sorry for being the bain of your life on this BBS! Quote Link to comment Share on other sites More sharing options...
Chris Wilson Posted January 21, 2002 Share Posted January 21, 2002 Quote: from Alex Holdroyd on 1:40 pm on Jan. 21, 2002[br]So are you saying if you find the T-66 at high boost can get you the power you want go for the T-70 or whatever to bring it down to a lower boost pressure for the same power...add the lag but think of the longer lifespan. And try to resist the urge to add that extra boost! Would you then try to reduce lag with over fueling (flames out the back job, from a motec ecu) or nitrous? Would you just put up with it? Would porting the head (especially the exhaust valves) and having 264i & 272e cams reduce the lag and help the spool up. Cheers Chris - sorry for being the bain of your life on this BBS! Decide the boost you need to run, work out the approximate amount of air the engine consumes (the tricky bit) pick a turbo that runs this air flow and boost at the best efficiency. Move map up and right for less lag, but less efficient high boost, lower and left for converse. Order turbo, fit and map to suit. Expect to play with housing sizes on compressor and exhaust one or two sizes each way on both to optimize (Easy on an engine dyno, PITA in the car). That's about it. Forget anti lag on road cars, too destructive. If anything the 2JZGTE could do with bigger exhaust valves. 272 cams on both intake and exhaust are still very tame, but fine for road usage. Expect a LOT more lag than stock, and IMO these mods need a manual transmission, the engine falls flat with an auto and doesn't work nicely at all. If a lower diff ratio is available use it. I just hate web based miling lists, too time consuming! Quote Link to comment Share on other sites More sharing options...
Syed Shah Posted January 21, 2002 Share Posted January 21, 2002 Lower diff ratio? Wouldn't that mean longer gears? If it does, wouldn't that just make the lag even worse...... or am I getting confused Quote Link to comment Share on other sites More sharing options...
Ian C Posted January 21, 2002 Share Posted January 21, 2002 I think it makes the gearing longer, so you spend more time in each gear. This means a large-lag turbo will get up to speed at a lower rpm (turbo spinup speed is dependant on gas flow, not strictly an rpm value, you see) thus giving you more rpm to play with at full boost. I don't know enough about this to hazard anything more than that guess, though. -Ian Quote Link to comment Share on other sites More sharing options...
Syed Shah Posted January 21, 2002 Share Posted January 21, 2002 I thought it only gives you more mph per rpms, and that the longer gears would slow you down. Which is why rally cars etc have their gears as short as possible. Quote Link to comment Share on other sites More sharing options...
Ian C Posted January 21, 2002 Share Posted January 21, 2002 Yes, that's entirely correct, but these rally cars have fearsome anti-lag systems, so they don't have to worry about the lag. Upping the gearing on a big single/twin setup would mean full power for say 4500-6500rpm instead of 5500-6500rpm, which would more than make up for the longer gearing. I can't quote any figures or anything, I'm just thinking about why the longer gearing would be better, and that's the only reason I can come up with. The torque factor may come into play as well, a big turbo will give loads of torque when it's on song, so longer gearing is a good thing, the acceleration will still be fantastic. The Porsche whaletail GT car only had a four speed box, and it would hit what, 230mph?!? It had sooo much grunt that shorter gears would have been wasted on it. -Ian Quote Link to comment Share on other sites More sharing options...
Syed Shah Posted January 21, 2002 Share Posted January 21, 2002 That brings me to another thing That is, I think that the first four gears in the TT are pointlessly short, what diff would be better, not only for this lag stuff, but for lenghtening the gears significatly (so i could use 4th for all overtaking rather than being stuck between it and 5th). I would have thought something like a 2.950, or a 3. Back to you Ian + CW Quote Link to comment Share on other sites More sharing options...
Chris Wilson Posted January 21, 2002 Share Posted January 21, 2002 Quote: from Syed Shah on 8:44 pm on Jan. 21, 2002[br]That brings me to another thing That is, I think that the first four gears in the TT are pointlessly short, what diff would be better, not only for this lag stuff, but for lenghtening the gears significatly (so i could use 4th for all overtaking rather than being stuck between it and 5th). I would have thought something like a 2.950, or a 3. Back to you Ian + CW Finger / brain interaction trouble, I meant the lag could be helped with lowering the potential top speed to something more modest perhaps, via a diff ratio change. The stock 6 speed hasn't got very nice ratios anyway, so ideally a gear kit with different ratios might be the better option. Quote Link to comment Share on other sites More sharing options...
Ian C Posted January 21, 2002 Share Posted January 21, 2002 You see? I told you I didn't really know what I was talking about I was just trying to think logically (I knew I was going wrong somewhere) I like the stock 6 speed gears, but I can understand what you mean - 1st is fairly hopeless for wheelspin, 4th to 5th is a noticeable ratio hike, and you need to drop to 4th for overtaking (but that's an artefact of the sequential setup - you need 4000+rpm to get all your power). I love the idea that it's geared for 200mph at the redline. I'm a high speed cruiser myself and I wouldn't swap it for anything. -Ian Quote Link to comment Share on other sites More sharing options...
Alex Posted January 22, 2002 Author Share Posted January 22, 2002 Slightly off topic, but, The Quaife Sequential or Manual 6 speed gearbox comes with the gears of your choice. I had a play on their site with the gearbox creator/config tool and settled for a gearbox which hit 205mph in 6th at 7,000rpm 2.8k rpm drop between first and second, first was capable of about 50mph (low enough to keep it driveable in town). If I was drag racing the car I'd spec a first gear which cleared 60mph as big power allows you to use longer gears and thus change less. The gearboxes themselves are about 5k to buy which is alot but it might be worth it to have a set of gears which match your cars powerband. Just FYI. ******* Ian, Your argument was logical in a way, but you can't help it when the experts we rely on trip us up! Think Chris was just testing us! Quote Link to comment Share on other sites More sharing options...
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