James' Civic Rebuild Thread + High Power ER Motor Theory

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James' Civic Rebuild Thread + High Power ER Motor Theory

Postby James » Tue Sep 04, 2007 10:10 pm

Hey all,

Ive been thinking about what an appropriate turbo to make 200HP in a street driven city motor is. I think 200hp is a realistic goal for a moderately worked street driven car with a good tune.

I recon due to the special characteristics of the city motor it needs a reasonably special turbo choice.

Firstly it has a very low bore to stroke ratio. What this means is that piston speeds are relatively high, which in turn means high intake velocities meaning good low RPM torque. The offset is that there is not much room in the bore for valves, so the engine can't breathe very well in the high revs because of this (lowering the volumetric efficiency).

This decrease in volumetric efficiency can be offset to a certain extent by running a higher lift and longer duration cam (or bigger valves but you cant go much bigger at all). More camshaft lift is a good thing, gives you more torque over the board, is just harder on your valvetrain. Having more duration hurts your low RPM torque, something turbo motors don't particularily like so we won't go there.

SO all this means we are never going to make much power over 6000RPM, its just the physics of it. With a decent cam and some headwork we might be able to stretch it to 6500 but not a lot furthur.

This all leaves us with a relatively narrow rev range in which to make some decent torque, say our target zone is about 3500-6500 rpm.

I have a lot more to say about increasing volumetric efficiency and will do so tomorrow :D, (actually today, its past 12)

I have been playing around with online turbo calculators all night and I have found a turbo which I think is perfectly matched to a 200hp city motor. Its a TD04-09b from a twin turbo Mitsi GTO or legnum.

Todays lesson shall end there :D
Last edited by James on Tue Apr 17, 2012 12:03 pm, edited 3 times in total.

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Postby sin-city_turbo » Wed Sep 05, 2007 3:57 pm

Great to see a good grounding for a discussion on turbo selection!!

I have thrashed a Familia GtX with a TD04, it made very good power from low RPM, probably somewhere around 3000rpm (which is a good thing for our engines), and boosted hard up until about 6000rpm where it seemed to drop off (another semi positive for ours), in the end he upgraded again to a Td05 from an evo, which shifted evryting up 1000rpm or so.

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Postby James » Wed Sep 05, 2007 8:36 pm

Cheers for your comments Sin city :D

I did even more playing around with values and stuff today and it turns out I wasnt really accurate in saying that the td04-9b would be a good turbo, its in fact far too small. I had made a bit of a cawk up in choosing the efficiency of the engine by choosing it too high.

OK so to make 200hp we need to run about 25psi, this seems about right from looking at at peoples past dyno runs. This equates to a pressure ratio of 2.75. This means atmospheric air is made 2.75 times smaller in volume to compress it.

To make 200HP at this pressure and at 6000rpm we need to run about 300CFM of air, or 21lb/min. This is a fair wack of air and its very difficult to find a turbo that will flow that much at such a high pressure ratio. One compressor map that seems fairly accurate is the one shown below.

Image

This is a Garrett T3 45 trim compressor. The points plotted on this map are 3000rpm, 3400, 3800, 4900, 6000, 6250, 6500. This theoretical city engine makes peak power at 6000rpm (500rpm higher than factory, very realistic with cams, exhaust and intake mods.) and is making full boost by 3500 (this doesnt mean it actual will, its just for the sake of plotting the points). This is pretty much the only compressor in the databank of the calculator im using at

http://www.squirrelpf.com/turbocalc/index.php

that even comes close to getting all the points anywhere near the efficiency map.

Now comes the joyus part, after MUCH MUCH MUCH internet whoring I found some interesting info on a mazda GTX forum:

T25 - Commonly found on the CA18DET S13 Silvia's and 180SX. Compressor - 45 trim T3 wheel with 0.48 A/R T25 diffuser Turbine - 1.77" wheel (62 trim), 0.49 A/R T25 housing


SOOO the t25's of ca18det's (s13 silvia K's among others) have the correct T3 compressor wheel we are interested in!!

These are as common as dirt over here, the turbos sell for less than $200 as anyone worth anything upgrades their silvia's to a bigger turbo like a t28. The other lovely thing is that they have a nice small exhaust housing, 0.48 A/R is about exactly where we want it.

I am currently after one on TM at the moment thats a single turbo off a 300ZX, it appears to be the same as the CA18det turbo so heres hoping I win it! (none of you steal it!!!)

OK so now we have found a turbo thats going to work quite nicely to get us to the magic 200hp, we need to think about what other modifications are going to be required to get the volumetric efficiency of the engine up in the 90%'s at 6000rpm where we want it.

Throttle bodies: I think this is probably the singly most restrictive part of a city turbo breathing system. They just dont have anywhere near the area that the intake runners or the valves have. Not sure why this was done, perhaps it keeps intake velocity and torque up, maybe it makes lots of turbulence to help mix the fuel or something, anyway its not good for high performance. I plan on replacing mine with a ~60mm one either from a CA18DE (which I coincidentally have one sitting around) or a ~62mm one from a b16a which colza has previously used on his abomination of an intake manifold. I am going to keep the CVCC throttle body, it will be attached to the main throttle system by some linkages, I havnt sorted this out yet but thats how it will be done.

Exhaust manifold: This is probably the next most constrictive thing in the breathing system. Since I am fitting a larger turbo with a different fitment I am going to make an equal length tubular manifold anyway, so this wont be an issue.

Intake Manifold: I recon this is probably the next most constrictive thing in the breathing system (there isn't much left :P) The hard 90 deg turn from the throttle bodies into the manifold can't be good for flow, its just gonna make it so nasty and turbulent. However members have previously stated that the factory manifold with a bit of a tickle would be good to 200hp (charles), but on the other hand with a decent straight runner log plenum style manifold you could probably get there with a few PSI less boost. So that is what I am gonig to make. I plan on cutting the original one off just behind the injector bosses so I can use the factory ones of those, but I will weld on new straight aluminium runners.

I have not decided on a good length for the intake runners. Staying close to the stock length will probably give good results in that low down torque will be boosted, but on the other hand I don't want to hurt high rev performance. Luckily with turbo cars this measurement is less important than with N/A cars. Staying close to the factory length will probably be wise as it should keep off boost performance torquey. Then when you are running higher boost the length doesn't matter so much I don't think.

I am going to keep the CVCC runners and run them seperately in their own little pipes. Will be a bit tricky to weld But I think keeping CVCC is a very wise move.

CAMS: Thanks to Charles we have specs for the cam duration of the Mugen racers(235degs at 1mm lift on both intake and exhaust) , I will probably have my cams groud to these specs and go with the cam grinder on what sort of lift I should run on a pretty much stock valvetrain. Correspondingly if anyone can remember the max lift value for a stock T2 that would be handy. EDIT: Just remebered the tighe cams website, it has stock lift's for the 12v honda of 8.9mm and they bump it up to 10.1 for a mild grind. It sounds like its ment for an NA honda motor so Im not sure how close that would be to the measurements of a T2.

Intercooler: The one I have got is going to be big enough I recon, expecially because it it mounted neatly next to my radiator and gets HEAPS of airflow there.

OK so thats my plan of action. Of course I will have to tune my fueling to get the powers I want but I have an idea for that, more on this in the coming months :D

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Postby James » Thu Sep 06, 2007 1:24 pm

Well 20 mins with a hacksaw and i have cut the flange and injector mounts off T2 manifold all in one piece. The ports are very strange in their design and it looks like quite a few comprimises were made sacrificing power and flow for compactness and idle smoothness etc. I will post up some pics later on.

As for using it as a base to make another manifold off it would take a fair amount of welding and grinding back to get it to look how I want, so I might just CNC a new flange from some 30mm plate, wont be a very complicated machining operation and will make the fabrication of the manifold HEAPS easier.

I also took some measurements off a reasonably tired T2 camshaft, it would appear to have around 6.8mm lift +- 0.3mm. with about 3mm on the cvcc lobes. I have a feeling this is quite worn.

Also made some decisions regarding port sizing. I am going to run 32mm ID tubes on the exhaust manifold, this is a couple of mm bigger than the standard ones but not a lot, should be good to decrease the back pressure a little but not slow the gas down lots.

Also going to run about the same size on the intake, the standard manifold is about 29mm at the port so I will try to run about a 31mm runner.

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Postby Hyperblade » Thu Sep 06, 2007 5:37 pm

So what would you do if you were going for around 130-140hp and as much torque as possible.

And as good throttle response as you can get?

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Postby James » Thu Sep 06, 2007 7:45 pm

T2 turbo would be perfect for that, maybe even a T1 turbo at a stretch. I take it you mean at the engine?

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Postby Hyperblade » Thu Sep 06, 2007 8:24 pm

bigelboe wrote:T2 turbo would be perfect for that, maybe even a T1 turbo at a stretch. I take it you mean at the engine?


Yep

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Postby James » Thu Sep 06, 2007 10:21 pm

You will make about that at the engine without even an FCD on a T2... Exhaust and boost to 14.5psi

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Postby Hyperblade » Fri Sep 07, 2007 3:47 pm

What other mods would you suggest to engine to increase the response/ low down torque?

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Postby James » Mon Sep 10, 2007 3:53 pm

HyperBlade wrote:What other mods would you suggest to engine to increase the response/ low down torque?


Damn it all!!! I forgot about the bloody auction :(

OK hyper, depends how hard out you want to go.

A cam grind to increase lift but not touch duration will help your torque.

Smoothing of the casting dags off the manifolds and head will help keep port velocity high and thus increase torque.

An equal length tubular turbo manifold would make a significant difference to your torque and turbo spool time. If you have some basic fabrication skills and access to a welder it might be worth making one yourself.

Im not sure about the intake manifold, at a guess you could probably get more performance from an equal length runner system with a single well chosen throttle body and correct runner length but Im not sure this would be worth the gains, as you would probably want to heat it with coolant to get good fuel atomisation aswell. Probably filling down the shafts either side of the throttle bodies and maybe getting a small oversize on the main throttle body would help, Charles said that the filling down of the center thing helped torque all over If I remember correctly.

Bump the static compression, easiest way to do this is mill the head right down close to the limit. But if you do this it retards your cam and ignition timing so you really need to get an adjustable cam wheel on there, or else your shooting yourself in the foot a bit. If you measure how much you mill off the head you can work out how much it retards your cam timing.

High flow air filter.

High flow exhaust.

Boost controller to hold the wastegate closed until you reach boost (MASSIVE difference in torque.) What we have talked about will handle this tho.

Thats all I can think of at the moment, but I emphasize the last one, when I first put my home made boost controller on my car it made such a huge difference to the onset of boost, it came on so savagely.

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Postby James » Mon Sep 10, 2007 5:47 pm

OK I changed the topic to suit where this thread is heading better :D

Image

Image

Image

Image

OK so I have decided the ports don't come off this straight enough for me, it would require too much welding and grinding back to get the ports where I want them. Sooo I am going to mill version with straight ports and little flanges to weld pipes onto on the CNC mill at uni :D The last picture is showing the slab of alu I borrowed from work to make it out of :D

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Postby James » Tue Sep 11, 2007 8:36 am

I have bought a ca18det turbo, should be here later this week, will be buying steam pipe for the manifold within the next few weeks aswell.

Going to do a back-purged tig welded mild steel turbo manifold, figure its not worth going for stainless just yet.

If you hadn't already gathered, yes, I am embarking on a 200HP ER build :D

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Postby city_cabriolet » Tue Sep 11, 2007 9:15 pm

I have a t25 from ca18det in my shed, never got to install it.

That and a spare T2 computer, i should dig them out and sell them...

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Postby Hyperblade » Wed Sep 12, 2007 3:42 pm

Thanks for the info Bigleboe, was much inline with what i was thinking.

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Postby sin-city_turbo » Thu Sep 13, 2007 10:46 am

what BOV are you going with, Bigelboe? Plumb back?

I have a brand new ssqv BOV but have been offered a Plumb back, which with help alot with keeping my vf10 spooled


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