ALFAGTV6.COM

[GarthW]

Hi all. Got a couple of questions to ask...

My last dyno session was interesting, but then again it wasnt...
Interesting that we realised the coil was pretty well dead, and after changing it to another coil it was much better, and sounded very nice.
But not so interesting was the fact that the old girl was only making around 170hp at the rear wheels on 12psi. Basically i'm not sure if my turbo is too small, but then again its a 460hp turbo, so i'm abit puzzled why i'm not getting more HP.
I've been told the engine simply cant make too much HP because of the plenum and intake runners, but after reading afew of the posts you guys have written, that isnt so much the case...

Yeah i've said i was going to enlarge rear exhaust housing to an 0.86 from the current 0.64, so i'll have more mid-range to top end grunt, but with the current setup boost comes on very quick and strong down low which is what i originally wanted.

Can anyone tell me if they think the turbo is too small..?

Next dyno session will run 15-16psi and see what that produces..but basically i'm expecting, or was expecting around 250hp at the wheels without much fuss. I thought with a 460hp turbo that it shouldnt be a problem. If i wanted 180-200hp at the wheels, i simply would have gone with a n/a 24v and be done with it.

Also my brother, which in the past he has done alot of drag racing, said the standard cams may be restricting..? Where me personally i've always thought standard cams are just fine, for its the turbo that makes all the power..?

Basically i was expecting more. Changing intake runners and plenum will be expensive, for injectors would have to be changed, etc.

Does anyone have any hp figures from a boosted 2.5 12v gtv6..? And what boost was run to achieve that..?

In the end car is going very well and its quick to say the least, but i want more than 170-180hp at the wheels. Yeah its making alot more torque than a 24v sure, but why such low HP figures...? Maybe with 16-18psi i'll hit 200hp with abit more ease..? 18 psi is the sweet spot with this turbo, which is what i was told when i bought it, so maybe i should simply wind it up and see, but dont see my clutch lasting with that boost pressure. As long as i dont launch it i'll be fine...

Thanks for any help guys.

[SydneyJules]

Power at the wheels is simply a measurement, Garth- it isn't everything.... how does the car drive? If it goes well, don't go changing shit to arrive at a figure that sounds good when you're at the pub with your mates! Do you really want more? (of course you do)

If you've got room in the fuel flow - ie injectors are big enough, fuel pump is big enough, and the computer can handle the increase, then gradually bump your way up to 18psi, and get it re-tuned for that, providing engine, turbo and exhaust will allow it..

I don't think it's at the point where you should start chasing plenum and inlet changes-

1) You're no where near the level of power where it is going to make a difference (not meaning to sound demeaning at all- just a straight statement)
2) You're squashing the air up and jamming it in there, so it isn't as though it's an NA donk that really needs plenum and runners sized to match desired rpm bands.

*What are your comp outlet and throttle body inlet temps?
*How quickly does your engine arrive at full boost ie RPM and Load- full throttle at 3k rpm?- as a measure of whether or not the turbo is sized correctly- If you spin it any harder than what it can deal with, all you will do is spit out hot, turbulent charge air. Maybe you do need an exhaust wheel change as you've talked about? It could be choking it and arriving at its' peak so early in the rpm range that a further increase in exhaust volume and speed are more than it can cope with
*How well is your exhaust sized for the amount of boost you want to run?
*Is there any chance your new exhaust manifolds are causing the issue?

If you were to build an engine revving to 8k rpm under 30psi with serious rods and crazy headwork, then Runners and plenum will make the difference, for sure, but I don't think you're at that point yet...

See what Kev and Greg Gordon say about their experience, but I think the problem is elsewhere.

Don't go chasing that path with heaps of cash when you aren't efficiently, as far as you could be with what you already have.

[ChrisS]

I'm not sure if it's any help...but my recent experiences with my supercharged 3l. 7psi rising to 8 from about 6k, gave 256bhp at the flywheel and 261lbft. I did some guestimate calculations. Assume 30 bhp to drive the blower, that gives 286bhp, divide that by 1.5, gives about 190bhp....which is pretty much what you'd expect for an aspirated 3l 12V motor running at 8.8:1 more or less....so, what would you expect from your motor aspirated? Multiply by 27/15, to give you a guide. Yes, I get that this is very rough and ready, but it'll help to see if you are in the right area at least.

It's emotive....but I'm with the rr operator I use on this, RWHP is almost totally useless, except as an indicator for the same car, same day, same conditions, and even then it's not hugely accurate. Unless the dyno does an accurate run-down correction to predict back to flywheel HP, comparing one car to another is uttterly pointless IMO - far too many variables.


FWIW, my car indicated about 212 RWHP IIRC for a 256 flywheel figure. Change gear, change loading on tyres, change tyre pressure - RWHP number changes a lot.

YMMV !

I'll second what Jules says too - how well is it driving? I'm dissapointed in the boost figure I'm getting, and the power figure reflects the boost.....but does it drive nicely!!

At least with a turbo it's realtively easy to wind the boost up - not so easy for me. I'd expect a good 300bhp at the flywheel from 12psi on mine. If I can find my missing boost, I reckon that'll do me.

[Duk]

Garth, regardless of what coil you are using, take it and the distributor and place them firmly in the bin .
OK, I'm being dramatic, but you really really should move to a multi-coil ignition system. You have the computer to do the job, you just need the new hardware.

It may not be the total answer to your HP challenge, but you are going to be limiting your overall results with 1 poor old coil trying to deliver spark to densely packed combustion chambers via a distributor and long ignition leads.
The harder you rev it, the worse it gets.
The more boost you run, the worse it gets.

[Mats]

If you suspect the coil and everything else is on the large side I'd DEFINETLY try another coil. You sure don't (shouldn't) bin the dizzy. Just remove any kind of vacuum advance if you have programmable injection and get a good coil.
I'm building my new engine with an MSD Blaster2 coil + MSD 6A amplifier. Have used that in the past on other cars with truly amazing results. Very easy and cheap way to go compared to COP.
My old Saab went from coughing, sputtering drone when my final injector kicked in to a 100-150Km/h dash in 5 seconds in top gear with the MSD. The stock coil didn't like rich mixture and 1.6 bars of boost. with MSD it just went like stink, even if we opened up the plugs to 1.2mm...

My GTV ran just fine with 3 out of 4 center electrodes completely eroded away, easily 5mm gap for the spark... Couldn't even tell the new plugs were in if I didn't know it.

[la_strega_nera]

What are your turbo size and a/rs?
Could be that you're just not in an efficient part of the compressor map?
Look at what the single turbo 1JZ guys are achieving with 2.5l for sanity check on turbo size/a/rs/boost numbers.

[4SFED4]

A 460BHP T2 based turbo does not really exist, whether .64 or .86 A/R. Even with a compressor that will flow the 43-46 lbs required to generate 460BHP it will be restricted on a T2 turbine housing. Look to the T3 family of housings the .63 A/R will give you more response and the .82 A/R more top end.

Based on your quoted power figures there is a restiction somewhere, it still could be on the intake but the turbine housing is a given. Start with the low hanging fruit first.

Good luck.

[GarthW]

Thanks for help guys, greatly appreciated!!

Jules-Yeah your right, why i'm concerned about the HP now, well i think with what i've spent i was just expecting more, but yes the car drives really really well, amazing down low torque and boost holds very steady. Inlet temps were very low around 30degress.
Comp outlet temps i dont know, but will know on next dyno run for i've now got a insert in exhaust to read temps there. Maybe new manifolds are restricting top end power, but down low its sooo much better now. Running full 3inch exhaust, rear muff is straight through.

Chris-Great HP figures there on low boost, the 3.0 gives more grunt for sure...

Duk- Yeah i'm still running old dizzy, i think your right, well i know your right!
Will change to a better coil pack for sure.

Ben- Turbo size is 0.64 front housing, rear 0.60. GT2871R was down sized abit for low down power.

4sfed4-Yeah that sounds good, will look at the 0.82 for abit more top end for sure.

Again thanks everyone, basically i should be happy with what i have, great low down torque and reliable setup, but yeah will give final power figures once another tune is done with another coil pack and 1bar-18psi run.

[ChrisS]

...... basically i should be happy with what i have, great low down torque and reliable setup,......

same here......but like you Garth, I'm not!! It must be contagious

[Duk]

...... basically i should be happy with what i have, great low down torque and reliable setup,......

same here......but like you Garth, I'm not!! It must be contagious

Don't worry, it doesn't just apply to Alfa Romeo's (or just their engines)

Much like Garth, my turbocharged/supercharged MR2 has some pretty ordinary outright performance. It's got some excellent midrange grunt, but the top end....... Meh .
I attribute most of that to poor exhaust manifold design and weak, standard ignition system.

I think it's just the Petrol Heads inherent desire to want to get as much out of their person input (read: horsepower ) as they can.

[GarthW]

He he yep, its abit addictive thats for sure..

I mixed up the a/r specs before, rear is 0.64 and front is 0.60.

I'm thinking now the turbo is pretty small for a V6.
Have been talking to a guy who does jap cars and stuff, and he said that the turbo i'm running, is one less than a RB26 setup, basically a R34 nissan skyline runs 2 of the same turbo on a twin setup. And thats a 2.6 straight six! So maybe down the track i'll change turbo...when i heard that i was quite shocked, but all good.

[Mats]

A/R is only half the story, we need wheel sizes or housing sizes (or a turbo series name or similar) to be able to figure out what power figures you can obtain.

[4SFED4]

The GT2871R is made by Garrett. It is a hybrid between the GT2860RS and the GT30R's. Since it is a .64 T2 it can be only one exhaust wheel, the 53.8mm wheel. It's a GT2860 exhaust wheel mated to a compressor wheel almost the size of the smaller GT30R, terrible combination for any motor.

The compressor wheel is big enough but the turbine whell and the housing are too small. Have it rebuilt with a larger turbine wheel and the .63 A/R turbine housing and you will be over 250WHP at 10psi and over 300 at 1 bar and you will have even bigger midrange. Go for the .82 A/R if you want over 400BHP.

[Mats]

hah! Sorry for my useless reading abilities, now that 4SFED (Jim?) wrote it I found it in your previous reply Garth...

[Giuliettaevo2]

Just sell the turbo and put a nice fat Holset HX35 on it...

I reckon mr 4SFED4 knows a thing or two about turbo's. Remember seeing a license plate with that lettering on the rear of some old Alfa on a website somewhere...