Adding a turbo to a high cam lift engine

Adding a turbo to a high cam lift engine

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TotalControl

Original Poster:

8,017 posts

197 months

Saturday 6th February 2016
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Started a top in GG but this may be more appropriate a place for discussion.

I'm not going to pretend I know a lot about the ins and outs but curiosity got the best of me.

Lets take 2 engines that are relatively the same. Say, for example, the Celica Gen 7 140 and 190 engines (1ZZ-FE & 2ZZ-GE if memory serves me). If one had to be chosen to turbo charge, which would be more effective? Also, which could be pushed further? Would the VVTLi in the 190 allow for the turbo to kick in and the lift after, or would the lift be made redundant?

Educate me.

Other examples of the same type of engine could be used by you guys who are a lot more knowledgeable as examples, but none spring to my mind right now.

Luther Blisset

391 posts

131 months

Saturday 6th February 2016
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I'm just a layman like you but to me torque is a function of airflow and airflow would help spool up.
The 1ZZ makes peak torque at lower rpm than the 2ZZ but if the latter still makes more torque everywhere I think maybe it would spool quicker.
I'm assuming things like friction etc is equal right the way through here, and ignoring things like compression ratios etc, which I guess is what you want for this hypothetical scenario?
I'm sure one of the professional engineers will slap me down in a short while.

battered

4,088 posts

146 months

Saturday 6th February 2016
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IANA Engineer, but here goes: the problem with lairy cams and turbos is that of cam overlap. In a non turbo engine the inlet valve and exhaust valve can be open at the same time. Because of the fact that moving air has inertia, you can afford to have this happen with minimal inlet charge blowing straight out of the exhaust.

Add a turbo and this all goes to pot. The fact that a turbo effectively pressurises the inlet tract and maybe even the cylinder before the compression stroke means that you can't afford to have the exhaust valve open, since if you do then the inlet charge just gets blown past the exhaust valve and out of the exhaust.

Apologies to engineers here for the simplistic nature of this discussion and the glossing over of any kind of analysis.

AdamIndy

1,661 posts

103 months

Saturday 6th February 2016
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A chap I used to kind of know had a supercharged 190 T Sport celica. It was brutal! With performance like that I wouldn't bother with turbo charging.

stevieturbo

17,229 posts

246 months

Saturday 6th February 2016
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Whichever has the strongest block/cylinder arrangement.

And the lift isnt a big deal, duration or overlap may be.

But depends on design of turbo setup and any expectations.

But none of it matters a damn if the base engine is a weak piece of turd

anonymous-user

53 months

Saturday 6th February 2016
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If you have an double overhead cam engine, which uses a separate intake and exhaust cam, then "overlap" is just the result of the basic cam timing you use. Valve lift, is irrelevant.

Assuming you have ports and profiling to support it, more lift = more air flow, more air flow = more power potential.

A typical production N/A engine at WOT peak power has a pressure ratio of about 0.85 generally speaking (98kPa intake, 115kPa exh), whereas a turbo charged version has a significantly lower pressure ratio, often as low as 0.5 (200kPa intake, 400kPa exh). All that a turbo does is to increase air charge density, it DOES NOT blow air into the engine, in fact, quite the opposite as the restriction of the turbine reduces the engines pressure ratio.

This means that turbo engines cannot run as much overlap (intake AND exhaust valves open at the same moment) because the momentum of the incoming air charge is not enough to prevent the much higher exhaust back pressure from pushing exhaust gases backwards into the chamber (on an N/A the higher pressure ratio allows the momentum of exhaust gases to continue to pull clean, fresh air charge into the chamber even when the piston is travelling back up on the compression stroke.


But as i said, as long as you can adjust the overlap independently then this should not be a big issue....

1st U.S. AutoProtect

1 posts

97 months

Wednesday 10th February 2016
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you are going to burn alot of oil doing that...

YankeePorker

4,763 posts

240 months

Wednesday 10th February 2016
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High lift valve engines are obviously designed to improve cylinder filling on normal induction engines. In theory the pressure developed by a turbo in the inlet manifold reduces the need for higher lift valves, improving the packing just by increased pressure differential.

High lift valves come with other constraints, stronger valve springs, increased cam lobe loads, lighter valves maybe more prone to overheating, etc. It would be reasonable to assume that a turbo combined correctly with the lower lift valve version of an engine at an appropriate compression ratio could give power more reliably and durably than with the high lift valve version.

But that's all theory, we need someone who has actually tried the experiment in the "suck it (or blow it!) and see" manner.

anonymous-user

53 months

Wednesday 10th February 2016
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YankeePorker said:
In theory the pressure developed by a turbo in the inlet manifold reduces the need for higher lift valves, improving the packing just by increased pressure differential.
er, nope. Turbo basics fail i'm afraid. Repeat after me everyone:


Turbochargers only act to increase manifold density, they DO NOT blow air into the engine


(The pressure ratio across a turbo engine (with very very few exceptions outside of the scope of this discussion) is WORSE than for an equivalent N/A engine, because the turbo has an efficiency less than 1)

Boosted LS1

21,167 posts

259 months

Wednesday 10th February 2016
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^ Could you explain this in more detail Max? It's an interesting statement. My boost guage reads pressure where an atmo engine couldn't.

anonymous-user

53 months

Wednesday 10th February 2016
quotequote all
Boosted LS1 said:
^ Could you explain this in more detail Max? It's an interesting statement. My boost guage reads pressure where an atmo engine couldn't.
And what does your exhaust manifold pressure gauge read??


Because people are familiar with "boost" gauges reading higher than atmospheric, it's easy to assume that a turbo blows air through the engine. But very few people stop to consider, and even less to actually measure, the pressure in their pre-turbine exhaust manifold at the same time. And because a turbo less than 100% efficient, it generally, takes an even higher exhaust pressure to make that "higher than atmospheric" pressure in the inlet manifold. I say generally, because under certain conditions, you can get a turbo engine to give a positive pressure ratio across the engine.

Boosted LS1

21,167 posts

259 months

Wednesday 10th February 2016
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Max_Torque said:
And what does your exhaust manifold pressure gauge read??


I say generally, because under certain conditions, you can get a turbo engine to give a positive pressure ratio across the engine.
This is the bit I like. ;-)

reggid

195 posts

135 months

Thursday 11th February 2016
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anyone used pressure equipment to measure cylinder pressure and port pressure to see whats happening in a turbo engine during induction regarding pressure ratios??

PeterBurgess

775 posts

145 months

Thursday 11th February 2016
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My mate Martin Faulks is experimenting with this on his most infamous Renault Alpine V6 Turbo thingies, he is using TFX stuff but is having problems getting clean rpm signal I think, not sure, I will see if I can get him to post.
http://www.tfxengine.com/

Peter

anonymous-user

53 months

Thursday 11th February 2016
quotequote all
reggid said:
anyone used pressure equipment to measure cylinder pressure and port pressure to see whats happening in a turbo engine during induction regarding pressure ratios??
Yes, pretty much every day for the past 20 years! We run high speed (10Khz bandwidth) water cooled piezo pressure sensors directly on the intake and exhaust manifold runners to record an engines real time pressure ratio, and generally to provide validation data for the fluid dynamics modelling and to validate the EGR systems (internal and external) performance etc

anonymous-user

53 months

Thursday 11th February 2016
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PeterBurgess said:
My mate Martin Faulks is experimenting with this on his most infamous Renault Alpine V6 Turbo thingies, he is using TFX stuff but is having problems getting clean rpm signal I think, not sure, I will see if I can get him to post.
http://www.tfxengine.com/

Peter
The TFX stuff is ok for a cheap solution, industry std in-cylinder measurement standard equipment is, and has been for 30 years, the AVL indicom system:

AVL_indicom

The down side is that a typical 4 cyl set up will cost you around £100k..........


Getting an accurate 0.1degCA crank position signal requires a precision encoder (usually a 3600 count optical unit) as the std engine CPS sensor ring has far to course a granularity and an unknown jitter.

Pumaracing

2,089 posts

206 months

Thursday 11th February 2016
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YankeePorker said:
High lift valve engines are obviously designed to improve cylinder filling on normal induction engines. In theory the pressure developed by a turbo in the inlet manifold reduces the need for higher lift valves, improving the packing just by increased pressure differential.
Ick!! Read this.

https://web.archive.org/web/20110918115242/http://...

YankeePorker

4,763 posts

240 months

Thursday 11th February 2016
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Pumaracing said:
Ick indeed! Hell, I was winging it anyway so no real surprise.

Boosted LS1

21,167 posts

259 months

Thursday 11th February 2016
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^^ Good read.

A good reason to use water injection imo. I used copper cored chargecoolers on my RV8 eons ago, they worked but added weight. Water injection works instantly and weighs very little depending on the tank size.

Beejayhay

120 posts

105 months

Thursday 11th February 2016
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One of the guys on GT4OC is putting out 700hp on a 5SGTE BEAMS engine which is VVti ...that's at the wheels! Build thread here.... http://www.alltrac.net/phpBB2/viewtopic.php?f=44&a...

sorry...cut n paste error..frown ... link sorted

Edited by Beejayhay on Thursday 11th February 14:51