Sizing a Single Turbo for RV8

chodjinn · Post by **chodjinn** » Thu Jul 24, 2008 11:43 am

As some of you know, I run a 3.9 twin turbo, using T04B Rotomasters. They're only at about 5-6psi at the moment, and have the legs for a fair bit more than that I guess.

However, I will be building another short motor soon, and I've been thinking about going to a large single turbo instead (mainly so I can sell my Janspeed kit on as I only use the manifolds and turbos now). So, I've been reading on the 'net about A/R stuff and turbine/compressor sizes etc, but seeing as I'm not very good at this I don't really understand it all. I'm mianly confused about sizing the turbine/compressor correctly.

The plan is for a 3.5l (215CI) RV8, and to get 'big power' (whatever that may be!) - now please don't flame or fill this thread up with crap about what an RV8 can take etc etc I know that, this is only a theoretical exercise. (bear in mind Prism have a massive power TVR twin turbo so it is possible with the right kit).

I've read about a guy in Oz running a Garrett GT40, (only apparently the GT series can't be rebuilt) and getting circa 500bhp. And I've been lo0oking at the usual suspects; Turbonetics, Precision, Innovative (if you can find one).

I have also been reading up on Master Power turbos (the proper ones not knock-off 'xspower'/'ssautochrome' shite) which seem a good budget equivalent, and I've also found a decent dealer in the US (e.g. MPGT45 for about $1k but it does look a big turbo!). I've also read through the forum, and generally speaking I should be looking at something in the region of .80 to 1.00 A/R turbine, with around .70 A/R compressor to get good power.

Anyone care to help look into this a bit further??? Sorry about the long thread for something so vauge

roofman · Post by **roofman** » Thu Jul 24, 2008 1:10 pm

chodjinn wrote:As some of you know, I run a 3.9 twin turbo, using T04B Rotomasters. They're only at about 5-6psi at the moment, and have the legs for a fair bit more than that I guess.

However, I will be building another short motor soon, and I've been thinking about going to a large single turbo instead (mainly so I can sell my Janspeed kit on as I only use the manifolds and turbos now). So, I've been reading on the 'net about A/R stuff and turbine/compressor sizes etc, but seeing as I'm not very good at this I don't really understand it all. I'm mianly confused about sizing the turbine/compressor correctly.

The plan is for a 3.5l (215CI) RV8, and to get 'big power' (whatever that may be!) - now please don't flame or fill this thread up with crap about what an RV8 can take etc etc I know that, this is only a theoretical exercise. (bear in mind Prism have a massive power TVR twin turbo so it is possible with the right kit).

I've read about a guy in Oz running a Garrett GT40, (only apparently the GT series can't be rebuilt) and getting circa 500bhp. And I've been lo0oking at the usual suspects; Turbonetics, Precision, Innovative (if you can find one).

I have also been reading up on Master Power turbos (the proper ones not knock-off 'xspower'/'ssautochrome' shite) which seem a good budget equivalent, and I've also found a decent dealer in the US (e.g. MPGT45 for about $1k but it does look a big turbo!). I've also read through the forum, and generally speaking I should be looking at something in the region of .80 to 1.00 A/R turbine, with around .70 A/R compressor to get good power.

Anyone care to help look into this a bit further??? Sorry about the long thread for something so vauge

5-6 psi...i own a nissan 300zx twin turbo which runs at 16-17 psi and have t25's it might be better to upp the boost on your own twins rather than going big...ive never been a fan of massive singles because of the lag till they spool up and the logistics in fabracation fitting a single from a V engine is a nightmare but its your call so goodluck

motherofgod · Post by **motherofgod** » Thu Jul 24, 2008 4:16 pm

Just a note, my friends twin turbo minor has two renault 18 turbo's on his, 1700cc for each side if you know what I mean, also Nick manns minor originally had a single turbo, not sure what it was but I'm sure someone will know out there for your reference..............I look forward to playing with my boost when fitted!

James

Eliot · Post by **Eliot** » Thu Jul 24, 2008 4:51 pm

Use Eric's turbo calculator:

http://www.not2fast.com/turbo/glossary/ ... tyCycle=85
(I have tweaked the VE and boost to give 480bhp - which i think is a bit keen for a weedy 3.5L lump)

GT40 is a pretty big turbo for a 3.5L rover. GT37 will do it, even a GT32 will take you up to around 350.

Give AET turbo's a call, they can spec one up for you - and base it around cheaper comercial (i.e. tractors/diggers) unit. Unless of course you want to empty your wallet on a fancy GT turbo (which I understand cant be rebuilt)

motherofgod · Post by **motherofgod** » Thu Jul 24, 2008 4:53 pm

Just found out Nick manns turbo was TO4B (what ever that is

)

James

IainB · Post by **IainB** » Thu Jul 24, 2008 4:58 pm

Have you checked out 'theturboforums.com' - hours and hours and hours of reading over there.
Just make sure you have done a search of the forum first before asking a question - as they have a habit of being a bit 'grrrrrrr' if you asking silly questions

BUT - its a brilliant forum for 'real' details about being blown

chodjinn · Post by **chodjinn** » Thu Jul 24, 2008 5:49 pm

thanks for all the replies guys. And nice one for sorting the turbo calc Eliot. Nick Mann ran a single T04B and had silly power out of a 3.5. I've already got two of them

As i said, just interested to see what sort of single turbo would work. 480bhp at 20psi, hmmm!

With the compressor maps, how do you know when the little red dot is in the best 'area' therefore you have the right sized turbo?? dont know how to read the maps!

What i'll prob do is bung on the two turbos i have and wind up the boost a fair bit!

Mark · Post by **Mark** » Thu Jul 24, 2008 7:13 pm

chodjinn wrote:
With the compressor maps, how do you know when the little red dot is in the best 'area' therefore you have the right sized turbo?? dont know how to read the maps!

You need to be as close to the centre of the 'island' as you can get at the pressure ratio your going to use if I remember correctly. It does not help that some maps are in LBs of air per minute and some in cubic meters

Mark

chodjinn · Post by **chodjinn** » Fri Jul 25, 2008 7:27 am

Thanks Mark, I sorta figured it would be something like that. I have seen various compressor maps with horizontal lines on them - is that representing different pressures?? I'm guessing that if you had the same turbo, and ran it at say 5/10/15/20psi you'd get quite different plots on the map?

Mark · Post by **Mark** » Fri Jul 25, 2008 7:43 pm

Here is a Map for the turbo I had on my bike, a guy that knows far more than I do emailed it to me and the scribble makes it easier to understand

For 7.5 Psi of boost you need to look along the horizontal line at the pressure ratio of 1.5 and for 15psi the line for 2.0 as the numbers represent absolute presure and include one bar/15 psi for the air pressure that is allready present in the atmosphere.
You need to stay away from the surge line

Mark

Eliot · Post by **Eliot** » Sat Jul 26, 2008 7:42 am

Marks map looks a bit like the ones I plot. Essentially chose a selection of boost pressures (pressure ratios, up the left hand side of the graph) and ensure the turbo provides enough air for the engine (along the bottom).

Keep away from the surge line on the left, dont go of the edge of the map on the right. And try to aim for the most efficient of the map - the "island" in the middle. You can go outside of the island, but its just less efficient, which means more heat - which is no good for best power.

I've written it up a little on my site with some additional links. There are plenty of pages on the net on how to read/plot compressor maps. Its pretty simple.

http://www.mez.co.uk/turbo1.html

chodjinn · Post by **chodjinn** » Mon Jul 28, 2008 8:28 am

I got lucky on ebay and just bought the biggest turbo I have ever seen for peanuts lol, so at least I can start having a think about fitting a single turbo in an MGB engine bay!

Eliot · Post by **Eliot** » Mon Jul 28, 2008 8:31 am

chodjinn wrote:I got lucky on ebay and just bought the biggest turbo I have ever seen for peanuts lol, so at least I can start having a think about fitting a single turbo in an MGB engine bay!

Lets hope it suits your engine. What is it?

chodjinn · Post by **chodjinn** » Mon Jul 28, 2008 10:01 am

Lol its another rotomaster, with exactly the same compressor as I have now (.60 A/R), but the turbine side is hoofing massive! Think its about 1.0 A/R but can't quite read it from the photos. Came form a 5 litre RV8 apparently, and for the price I got it for it doesn't really matter if its not suitable, it'll look wicked on my mantlepiece lol

kiwicar · Post by **kiwicar** » Mon Jul 28, 2008 12:35 pm

Are the "spin it up with a squirt of nitrous" aproach to turbo matching

look forward to this one!!
Mike

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