HTT 71 series

[cougar]

Any pros and cons on the High Tech Turbo 71 series?
I'm looking seriously at their "Super Stock" 62/71/14 because of its "low drive pressure" turban wheel.

[cedardiesel]

may be slightly laggy on a ve setup unless good injector used but will probably be pretty hazy tho.

[cougar]

HTT claims the larger wheel will spool sooner at lower drive pressures than smaller wheels. I have a lag now after I installed a 4" exhaust and I think it may be due to a loss of drive pressure.

[Richie O]

I have a lag now after I installed a 4" exhaust and I think it may be due to a loss of drive pressure.

Less back pressure should not make less power. It should help with spool, not hurt.

[Tacoclaw]

Less back pressure should not make less power. It should help with spool, not hurt.

+1

The only drive pressure in our system is between the turbine and the exhaust port. Anything after that is purely waste heat/gas and it's only job is to gtfo.

[Richie O]

A low flowing exhaust system could increase drive pressure just by the exhaust not being able to get out. But, like said above, drive pressure is the pressure in the manifold pre turbo.

[cougar]

It is not making less power, it is making more. It just has a big lag with smoke now.
So why do I now have a lag with the 4" exhaust? Nothing else has been changed and nothing is damaged or restricted. I went over every inch. What in my pump adjustments can I change?

[cougar]

I emailed Brandon at HTT on this. He said bad idea with the mods I have. Said I'd be better off with an HTB2 62/65/14. My lag is a drive pressure issue caused by the 4" hole. Not unusual for some applications.

[Tacoclaw]

I'm not about to argue with a professional, but I just don't see how that's possible. I didn't check your sig, but are you running a turbo with a clipped turbine wheel? That's the only way i could imagine it would let exhaust slip past the turbine wheel without having to help spool it.

Guess it's over my head...

[AHineman]

I think that the 65mm exhaust wheel will be better at your power level. I believe GLHS has run both and said that the 71mm exhaust wheel is more for trucks over 400 horse. As far as your lag issue, I can't say I agree with HTT. I went from crappy stock exhaust to a 4" downpipe and 5" all the way back and gained 2 psi of boost on my '93 with no increase in lag. It was enough of a difference that my wife said something about it running better. I called HTT when I was researching twins setups and was not impressed with their "help" choosing turbos. I told them what I wanted to price and they said "why would you want that?". Then they couldn't tell me why I should get something else, so I went elsewhere.

[dvst8r]

62/65/14 is as big as I would go on a VE, if you need more turbo after that, add a primary.

[cougar]

62/65/14 is as big as I would go on a VE, if you need more turbo after that, add a primary.

That is what I settled on after some more research.
I have noticed that everyone that has gone to a larger exhaust without issue also has a smaller turbine housing than my 16 non-gated. (One of the things that let to my decision) First considered an HX40, but that would be about the same as what I have now, hybrid H1C. I also considered a 62/65/12, but was worried about my EGTs going back up while towing.

[dpuckett]

I've put 4" exhaust on several trucks, with a variety of turbos (all H1C/HX35 based) and injectors, and NEVER increased my lag. If anything, it decreased it, because the turbo could breathe. This was with 14-18cm hsougins on the hot side, IIRC. Havent run a 12 in 10 years, and dont plan to go back to one.

You sure you dont have a boost leak somewhere? Not trying to be a smart ass, but it just seems counter-intuitive.

Someone told me a few weeks ago about a bigger exhaust cutting down on the torque, what was he smoking? The guy is into gas engines, no turbos. Is there something different in a NA engine than a turboed one?

DP

[cougar]

I understand, that is why I've gone over they system several time now hoping I missed something. No such luck. The only wild card that remains in this puzzle is my timing, I don't know what it is. So that is the where I am focusing my attention now. It may be too advanced and that is why I'm having this lag and may be why the M&H timing spacer didn't work either. I now have the tools to check it so all I need is a day of no rain.

Thanks for bearing with me on this, I haven't been able to figure it out on my own.

My related threads;
Under the KSB
This is getting old
Head scratcher