Brettus

iTrader: (2)

I know many will say I'm biased towards low mounts ..............and they would be right.
But I feel people need to think about the things listed here when they make the decision. Those with top mounts who disagree, I'd like to hear your opinions on the points I raise here.

Top mount downsides:
1/Heat from pipework and turbo into the engine bay extremely difficult to keep controlled without major attention to insulation detailing. This heat can cause premature failure of many components in the engine bay if not properly addressed.
2/Need to modify thermostat and run pipes around the turbo etc.
3/Most setups delete the omp which means you are forced to go 100% premix . This means the car loses much of it's practicality ... with the added hassle
4/Most setups delete the APV , which means to even get close to the powerband of a car that retains it, you need to run an extra 3-4 psi of boost .... adding heat to charge temps on an already compromised 10:1 compression ratio engine.
5/Performance is inferior . This is just physics. Turbos belong as close to the engines exhaust ports as possible. Putting it far away dampens the exhaust pulse energy and allows the air to cool somewhat. This is what drives the turbine, so poor spoolup and lower transient response can be expected along with increased backpressure.
6/Additional exhaust pipework makes the area beside the engine not only a plumbers nightmare, but puts a lot of heat into the lower intake manifold = bad.
7/ The lack of room for the exhaust also makes in extremely difficult to use appropriate sized pipes further decreasing performance.
8Aftermarket ECU open to engine bay with no cooling . While this isn't unique to top mounts , I mention it because I seem to see this so often on top mount setups. I really shudder to think how hot the electronics get and how this affects the reliability of the ecu. Give me the stock , well cooled and proven reliable OEM ECU any day.

Upsides to a top mount :
1/Bling factor . This is undeniably better with a top mount.
2/Ability to choose virtually any turbo you wish
3/Good accessibility to the turbo itself


Low mount downsides ;
1/Can't see the turbo
2/Cramped space available beside the engine means it can be very difficult to assemble and work on.
3/Turbo selection is very limited .... but there are excellent turbos that still fit.
4/Difficult to get full ground clearance ... not impossible though.

Low mount upsides :
1/Best possible performance if design is good.
2/No problem keeping full apv and omp funcionality
3/Potential for excellent heat management
4/Relatively unmolested topside pipework and wiring making for easier fitment and good reliability.

wcs

iTrader: (2)

Hey Brett, I'll add what I can.
You know my top mount setup isn't pretty but has served me well.
I'll just go down the list and comment where I can:
DOWNSIDES:
1) Yes heat management is a bit of a bear. Most of my coolant hoses are heavily wrapped including my the exhaust manifold and downpipe. I also use a turbo blanket which has its own pro's and cons. Other than that, it hasn't been quite to bad to manage.
2) Yes a modified Tstat housing would be the ideal solution but not entirely necessary. I do not have a modified T-Stat housing.
3) OMP Deletion - Well you've seen more setups than I have so I can only take you're word on this, but I still run the stock OMP. I've had to do some heavy heat management to protect the wiring harness.
4) APV removal - Huh I honestly didn't know this was a thing. I still have mine, no issues, no extra heat management. Now it will likely go and break on me lol
5) Agreed
6) I don't think this has been a plumbers nightmare. (maybe I'm not sure what you mean). As far as heat to the lower intake manifold, yes I've added a heat shield to try and mitigate this issue.
7) Agreed
8) I'm running the Stock ECU - Like you said overheating an aftermarket ECU shouldn't be a Top Mount only problem.

UPSIDES:
1) My setup has zero bling. Hope to address this over the winter.
2) Agreed
3) Agreed and I can't even begin to say how much this means to me. This point alone makes up for many of the downsides, at least for me.

Nice write up Brett - Cheers

Brettus

iTrader: (2)

Thanks for that WCS .
Good to know that you still have omp and APV . What type is your setup again ? Unfortunately most kitsets do delete these so it's something people need to consider when purchasing.

wcs

iTrader: (2)

Complete custom setup.
It's a Top Mount design using a BNR T04e 60-1 turbo charger.
The original manifold and downpipe was purchased from a forum member, IIRC it was fabricated by Mawnee (years and years ago now)
I can't even remember how long I've had this kit to be honest.
The original manifold and downpipe of since been replaced as the manifold succumb to heat fatigue. I found a local guy to fabricate new pieces based on that setup.
I think the manifold is 2.5" O.D (I'd have to go check) and the downpipe is 3" O.D

I was considering getting another set fabricated with a little more bling factor but I see you're producing a low mount manifold now ... so that got me thinking

jcbrx8

Here's a link to a similar discussion from 2016: Low Mount vs. Top Mount

I believe another low mount advantage / top mount disadvantage is ease of general, non-turbo related, maintenance w/in the engine bay. Top mounters please advise if you believe otherwise... but it appears low mounts are challenging to install / refresh, but top mounts have a good deal of challenge to install "well", e.g. OMP protection or delete, hose & wire re-routing, heat mitigation, etc.; and are more challenging w/r/t ongoing general maintenance.

Additionally, although there are a number of factors, e.g. specific turbo, intake / charge section dia., IC, control, etc.; beyond low vs. top mount that affect system performance; it'd be of value to see simple metrics for each: e.g. peak boost, dyno / VD, peak HP & torque. These metrics can give some indication of what "has" been achieved via each design type. At the end of the day I suspect that "performance" was high on all our lists of motivations for pursuing FI.

Could be a good discussion...not good or bad, right or wrong; but realistic expectations from each design.

Brettus

iTrader: (2)

Yeah , read that other thread before starting this one ... I think we have a lot more knowledge on the topic from those days so thought a new thread was worth it.

As far as performance goes ..... there is that much variation in the quality of installs and products used, that it's kinda hard to show apples for apples. One thing that stands out for me is that some of us (one in particular ) thought that the fastest spooling turbos in the world (BW EFRs) top mounted, would be a huge game changer. Results were predicted to be far and away superior to anything a low mount could do. That didn't happen and that in itself demonstrates how much top mounting kills turbo response.
Based on what I've seen over the years, I'd expect a top mount of the same size to lose anywhere between 500-1000 rpm of spoolup vs low mount.

Jose Zuma

1 pro for low mount:

• In countries where turbocharging an NA car is illegal, low mount is a great "hidden" solution.

1 con for low mount:

• Considering the space restrictions, it's hard to design a manifold that would keep the emap low (you have more room to play with a top mount).

Brettus

iTrader: (2)

A friend of mine went to some length to re-install the stock engine/battery covers and you would never guess it was a turbo 8.

Difficult yes ..... Impossible ?......... definitely not.
And while you have more room for the actual turbo on a top mount , the room for the up pipe and downpipe is limited meaning few systems are optimal in that respect.

KaneD

Thank you for the detailed information and for talking about the advantages and disadvantages. I've never dealt with a turbo, but I'm thinking of experimenting on my Chevy. I have not found the best turbo for 5.3 ls for my car, there is also a lot of information about the turbo system and how it can add horsepower to your car.