Old Slow Coach

I have a "race-ported" motor which either needs a rebuild or replacement. I know nothing more specific about the race-ports, except was told that I would "freak-out when I see them because they are so huge". Before I bought the car, it had a T-88 on it with nitrous. I was told the car used to make in excess of 650 whp. When I bought it, it had T-61 with q-trim wheel (compressor map attached), and it was a 500 whp car. It had very good top-end power for sure, but I'm not so sure if the low-end could be better.

500 whp is almost plenty enough for me, and I want to stay with the T-61 q-trim. I will probably turn the boost up from 1.5 to 1.7 bar. I believe if I ran say 1.9, it would still be greater than 65% efficient and I'd be making over 550whp.

My question is, with a T-61, and assuming I have about the biggest port job imaginable, am I sacrificing some low end and do I have more top end potential than I really need? If so, what port job would anyone like to recommend that would allow the full potential of the t-61 to be had in the top end, and not be any larger than need be?

Thanks in advace for your consideration!

bobybeach

When it comes to turbo charged cars then the porting has little effect on were you make your power, a well ported engine will only bring the boost on earliar or give you the ablilty to drive bigger turbos .
Its all in the turbo and how much boost you put through the turbo which dictates where you will see you you maximum torque on the rev range.

for example a small turbo like a to4b runiing at 1bar will make imediate power but will not produce any real tourque after 5500rpm on a ported 13b. if you run this turbo with less boost like .6bar you will continue to make lower but consistant power through to the red line with a nice flat torque curve.

if you go to the other scall and run something like a GT45 at 1.5-1.7bar then power will be all up top. and nothing untill 4.5-5000rpm then it will continue to make power all the way through to the red line with much stronger torque as a result of the higher boost levels.

a T61 is a good all round turbo on a ported 13b. id say at 1.3bar you will be at its limits now, and if you watched the boost gauge at high rpm you will probably see the boost droping off after 7000rpm since the compressor will be maxing out now.
If you want to bring the boost in earlier then use a slightly smaller turbine housing than what your running now, a t61 matched with a .84 will see good early torque.
larger ports will also bring boost in earlier but they will also mean you will suck dry the maxium flow of a t61 compressor earlier in the upper rev range resulting in loss of tourque/boost sooner, leaving you with less usable rpm.
you can overcome this by running less boost to insure the compressor dosnt reach flow limits until 7.5-8000rpm.

Old Slow Coach

I really appreciate your thoughts! According to my read of the compressor map, I should be able to stay within pretty good efficiency range at 2bar up to 7500 rpm. Am I reading it wrong or could you explain more your assessment about reaching limits around 1.3?

__dave__

it has less effect on where you make power, but is still very important. even the turbo bp's i've done have peaked past 8k.