1) how do you select a basic displacement, bore & stroke combo and compression ratio
unless we are building a class specific race car, or have an unlimited budget, its basically a run what you brung deal. dynamic compression ratio is the only real factor to consider and that can be played with thru the cam. iskendarian has been spec'ing fast turbo cams for a long time and they have a long lengthy history with camshafts and turbocharging.
2)how do you select the cylinder heads, port size.
some consideration needs to be taken for port size as it relates to expected power output. so it isnt a bad idea to get a larger port than you would in an NA application since port speed is affected differently when the manifold is pressurized. also as it relates to cylinder head flow, having a big bore is important for valve shroud reasons we talked about in another thread. valves and valve springs are very important, hollow stem valves will break with any real power, sodium filled valves seem to handle the stresses much better and are still very light. obviously it would be nice to get titanium wherever we can in the valvetrain, but sometimes those parts dont exist for the application or they are simply too expensive. on the exhaust side, again, with an unlimited budget i would use inconel valves in everything but sometimes its either impractical or out of budget. stainless steel at least.
3)what rotating assembly, crank ,rods, pistons, rings ETC.(obviously forged) but related info on set-up and clearances, ring gaps, heat coating, is welcome
most applications have a wider gap in the top two rings than you would expect in the NA world, the high heat from the extra air and fuel causes the usual gaps to close and then we have busted rings, pistons, and all around catastrophe. or you could use a gapless ring setup and not worry about it, but a certain amount of blowby probably saves more motors than it hurts. if ordering custom pistons its a good idea to have the top ring lower in the cylinder than a typical NA motor (something like you would for a big shot of nitrous) to add some clout to the top of the pistons. ive seen alot of people use coatings both on the piston face and in the combustion chamber to great effect. but i subscribe to the school of thought that if you rely on those coatings, when stuff inevitably breaks, you have alot of extra down time sending parts out for coating than just slapping your combination back together.
4) Header design, Size and construction
turbo headers on a street car are dictated way more than 75% by packaging. there are very successful turbo combinations that use factory cast iron manifolds with some sort of crossover tube setup for singles. also, theres a big market for turbo headers right now and theres alot of people making nice entry level setups for small block and big block ford and chevy of most generations that you can use as a building block to fit your application.
5) Crossover tube design, size and construction
a quick note about crossover pipes. a 2.25" crossover tube is good to atleast 900hp before it gets to be a restriction, so dont go crazy with a huge tube, its just gonna slow down the exhaust gas and cause lag my buddy had a great idea to use the wonderbar on c4 corvettes as a crossover tube and mount the turbo flange right on the square bar with the two headers low and straight forward into the bar. food for thought i know alot of us on here have c4's and packaging in that engine bay aint easy.
6) How do you choose the correct turbocharger make and model/flow map,and boost range
theres basically three methods, you can call a turbo company and take heir recomendation, use the software that we went over earlier in this thread, or you can use a turbo that someone else is using and hope it works with your cam, head, converter, and gear combo
7) Exhaust system basics feeding the turbo and leaving the turbo to exit the car
every time a moving gas or liquid has to make a turn in a tube, its a restriction. the turbines efficiency is greatly dictated by its ability to evacuate the gases that spin it. so have a very free flowing exhaust is IMPORTANT. theres alot of charts and tables here that correlate inside diameter of exhaust pipe to horsepower capacity, size accordingly and keep in mind oversizing (after the turbo) has no horsepower penalty.
8) Waste gate selection ,installation and optimal performance
if you want to run low boost pressures (14psi or less) on a large displacement motor that means alot of exhaust has to run out the wastegate instead of thru the turbine to keep boost levels down. therefore we need a larger diameter wastegate to control that large amount of exhaust gas. a smaller wastegate could possibly do the job at lower rpms but as exhaust gas volume increases, the smaller wastegates flow capability will be pegged and boost creep will happen.
9)intake manifold and throttle body selection
i really dont see anything working better than a single plane in any v8 application. it just moves the most air with the least restrictions, its the easiest to port, and most applications already have an efi version if you want to go that route so yea. single plane wherever packaging allows.
10) injector size and type selection
based on expected power output same as any other setup. figure for 85% duty cycle and add atleast 30% volume capability vs regular gas to your fuel system if running e85
11) heat shielding
i like to run a blanket on the turbine side at a minimum, it genuinely keeps underhood temps down and looks cool too. turbine housings get ugly like all the other cast iron parts on a car that reach cherry red glowing levels of heat. so a blanket insulates them and protects stuff from getting heat soaked and protects your eyes from looking at that crusty hunk of metal. i didnt mention it in the header section because i dont have enough experience with it but i havent seen a ceramic coating in person that can withstand the abuse of a regularly driven and raced turbo car. so header wrap would be a worthy investment on cast iron manifolds, however i wouldnt use the wrap on tubular headers for the same reason i wouldnt do it in an NA application, it ruins the headers and drastically reduces their lifespan.
12)intercoolers
we went over this before but briefly here, water to air is the best efficiency, but in a street car it isnt very practical. air to air works great but again in a street car you really have to make due with what you ot for space and packaging. guys with a/c probably feel it even more in the space department because of the condensor taking up room ou there by the front of the car.
13) engine cooling & lube system designs
same as any other high horsepower application, no special considerations different from NA in regards to operating temps or anything like that. the cars gonna make more power so expect it to generate more heat. both in the engine and under the hood
14) turbo lube supply
theres lots of ways to skin a cat and every application is different but basically tapping a pressurized part of the block typically near the oil pump outlet or after the oil filter and feeding that into he top of the cartridge (usually thru a restrictor orifice in a fitting like a banjo bolt or a nitrous jet with an orifice to turbo manufacturers specification) and the return of that is gravity, lord willing and packaging permiting, if gravity return is impossible youll need to utilize a scavenger pump of some sort. good luck with that
15) cams designed for turbo tend to have equal or lower duration on the exhaust to keep exhaust gas speed high and a
112-116 lsa to limit intake flow of fuel/air pressure exiting the exhaust
traditionally thats true and it definitely works. but theres alot of people who are using big NA style cams too as a way of maintaining performance while in vacuum or at the starting line. theres alot thats still developing every day in the world of camshafts and turbochargers.
16) the fuel lines and injectors will need to be calculated at near 85% duty cycle and BSFC of near 65%
17) AN#8 fuel lines and 200 GPH, or larger fuel pumps at 40-60 PSI are normal
some people running alot of boost pressure (like 50 psi or more) run very high fuel pressure to combat reversion thru the injectors. something to consider.
18) how to select rearing and converter stall speeds
turbo cars run a numerically lower gearing to build load and come into boost faster, the fat torque carries them thru the rpm's very quickly still. in a 240z i helped build when i was younger, with a 3.36 gear, the turbo came on hot and it felt like a bad ass NA car with 4.56's. as soon as you let the clutch out in first it was time to shift to second. as for converters hughes performance and PTC have alot of experience with converter for turbo cars i would trust their experts
19) solid copper head gaskets and ARP head studs are suggested as cylinder pressures are noticeably higher than N/A
20) BLOW OFF VALVES, bov, settings and size and location
on an automatic car i wouldnt even run a blow off valve. ive seen enough evidence to say that its really not necessary unless you have a manual transmission where you are going to be letting the throttle slam shut multiple times per pass... even then with the new antisurge technology thats out in turbochargers today its really more of a "i like the way it sounds so ill run one" type of deal
