How to convert lbs/min into CFMs...

[starscream5000]

Ok, here's what I've come up with, it's probably wrong, but I tried: at 10 psi the 7M is pumping out 512.6688 CFMs @ 6500 RPMs or 35.425 lbs/min. At 12 psi it's 555.3912 CFMs @ 6500 or 38.377 lbs/min. And at 15 psi it's 616.4232 CFMs @ 6500 or 42.594 lbs/min.

So with these numbers it looks like I'm riding right on the center circle's right sided line on that compressor map towards the bottom part, am I right? Where is the optimum performance of the turbo suppost to be at on the compressor maps?

 

[Doward]

The island of highest efficiency is the very centermost island.

When you want to hit that island, depends on what style of powerband you are looking for.

I personally like a strong midrange car on the street. I'm not so concerned with a MKIV big turbo style dyno graph - IMHO, for the street it is better to maximize your turbo right around 5500-6000rpm.

Especially if you are running stock rev limit. Kinda pointless IMHO, to just be getting into the turbo's 'sweet spot' only to have to shift again

Your calcs sound right - if you are on the right side (about to leave) the center island, you'll have a wicked powerband between about 4500-6500

*edit* Yep - @ 24psi, and 4500rpm you'll just be entering the 76% island - that thing must be a fun turbo on the street!

 

[starscream5000]

bear in mind this compressor map is of a GT61 turbo from ITS, not the BOSS turbo itself. In the message I got back from suprasport he said that ITS claimed that the housing on the BOSS turbo was much better, so they will differ some, but this should give a good idea of what to expect .

 

[jdub]

Yeah...looks about right to me too. If you can get the actual map for the BOSS, it would be a good thing. The term "better" might not be what you're looking for performance wise for a street turbo.

With this housing at 6500 rpm, 15 psi, and 616 CFM flow...2.5" piping puts you at critical velocity. I agree with Doward, you want to be getting near max at the 5500-6000 rpm range. See how it flows at 20-24 psi there and take a look at what that gives you for IC piping velocity.

 

[starscream5000]

At 20 psi it should be flowing around 720.1776 CFMs @ 6500 RPMs, which would put it around 10 ft/sec less than critical velocity on 2.75" piping, correct? I don't foresee myself going any higher than 20 psi (probably not even that) as my power goals are 450-500 reliable HP. So hopefully I'll be reaching this power output before I'll be needing 20 psi . So it's like this, I'd be running almost perfect velocity on 2.5" piping at 15 psi, or a little below 300 ft/sec at 20 psi, which I wouldn't see much of anyways. Looks like 2.5" piping may be my best bet. What I could do is get an intercooler with 3" inlets and outlets incase I decide to increase boost and piping size (will worry about TB later on down the road becuase I'm just researching right now) and only be out of the cost for new larger pipes. What do you guys think?

Edit:: It looks like at 5500 RPMs and 2.5" piping velocity is 297.9. At 6000 RPMs and 2.5" piping it's 324.9 ft/sec. So it jumps up really fast here at 2.5" piping and at redline it's 352 ft/sec. This is all at 20 psi BTW.

With 2.75" piping and at 20 psi it's 246.2 at 5500 RPMs and 268.5 at 6000 RPMs... Input please.

 

[jdub]

I would go with Plan A...2.5" piping with 3" IC inlet/outlet. Make sure the IC is sized to flow at ~ 750-800 CFM. The same applies to the TB...err to the little larger size.

You are really close to the velocity you want and it appears you are hitting the "sweet spot" in the compressor map. If you look at most dyno charts for the 7M, power peaks (and levels off) at about 5500-5800 rpm...plus (as you said) most of the time you will be in the 15 psi range. If the BOSS map is close to the one you posted, that would be a wicked street turbo...fast spool, good top end with a little room for growth.

How much did the psig increase from the 5500 - 6000 - redline?

 

[starscream5000]

Psig for 5500 (at 20 psi) is .73, at 6000 it's .87, and redline is 1.02... At 15 psi psig at 5500 is .54, 6000 is .64, and redline is .75... Forgot to add this in my last post: velocity @ 15 psi (2.5" piping) @ 5500 RPMs is 255, and @ 6000 is 278.1...

 

[jdub]

That's not bad at all for the 20 psi numbers...you are getting a psig increase over critical velocity, but it's almost linear. What you have to watch for is a big jump in a psig increase. I think you should go with the 2.5" pipes...it will keep velocity up and only a small drop in efficiency at 20 psi and redline.

 

[starscream5000]

Yep, that's what it looks like I'll be doing. Now when everyone reads this thread they'll know just why most people use 2.5" piping. Guys, both of you have been very helpful in this lilttle bit of research. Maybe the mods could put this thread in the tech section for a detailed reference on how the 7M engine breaths?

The good (or bad, depends on how you look at my addiction to power) part is, if I ever decide to go past 500 the only thing I'll need to change on the intake side will be the hard pipes (100-150 bucks, that's it). Whatever throttle body I use it will most likely be at least 2.75".

 

[starscream5000]

Ok, I'm having a hard time finding or getting feedback from various sellers on ebay on their intercoolers and how many CFMs they are good for. I PM'd Big A this morning asking if he knew the CFM ratings of his two intercoolers setup with the inlets and outlets on the same side, no feedback yet, but I have faith in him .

Since they moved driftmotion's sections out of misc. vendors I haven't been able to find his old thread on the spearco style intercoolers (I'll search again later, I only did a search in his vendor section at first). Anyone know the CFM ratings of some intercoolers that are spearco style?

Jdub, Would it be too bad to get an intercooler good for 1000 CFMs (this is around the amount of CFMs I'm getting replys on ebay from)?

 

[jdub]

The problem you are going to get into is pressure drop if you oversize the IC too much...be careful about this on the eBay IC's. Spearco IC's have a straight through fin design...a Spearco rated at 1000 CFM will not have a big pressure drop and will definitely be an improvement over stock. If you can, 700-800 CFM would be just about perfect for your goals. You also want to take a look at the efficiency rating of the IC...the Spearco would be an excellent choice in this area as well.

CarTech can custom make you an IC...I believe they are using Spearco cores...hold on to your wallet.
http://www.cartech.net/

 

[starscream5000]

Yeah, no joke on the cartech, I've seen 'em . I'm wanting to lean more toward Aaron's replica intercoolers. The pressure drop shouldn't be too much worse than a spearco version hopefully...

 

[starscream5000]

Ok, I got some feedback from Aaron. He said the spearco replica flows aprox. 800 CFMs... Perfect . I was thinking about going with his slightly larger version though, it's half an inch thinner, but it's longer. The dimentions of the core show it's slightly larger than the exact replica of the spearco IC (this would be just in case I had some growing pains ). What do you guys think?

 

[jdub]

Are there any fitment issues with the longer core? And what are the inlet/outlet diameter options?

Are the cores for both IC's the same a Spearco design wise?...i.e. the straight through bar & plate the Spearco uses? Any pressure drop or efficiency numbers for both cores?

 

[starscream5000]

Inlets and outlets for both are 2.5" unfortunately. If I ever decide to go with larger piping I would have to tig on bigger ends. I'll follow up on the other things when I hear back from Aaron.

 

[Doward]

I'm running Aaron's bigger Spearco replica.

You need to relocate the oil cooler, but I took the opportunity to go ahead and replace/upgrade my oiling system at the same time. Look at my build thread 'Finally getting started' in the Build forum if you'd like to see what kind of fitting issues you may have (just have to relocate the oil cooler, really!)

I went with full 2.5" mandrel piping all the way through, as @ 15-18psi on my 57trim CT26 @ 4500rpm, I should be hitting the sweet spot of my turbo, and from there as my intake begins to heat up (and decrease the air density) my flow should top around 291 ft/sec @ 6300 rpm. (80% VE and 18psi used)

With a set of 220º/226º BC cams, I expect to have a hell of a street Supra

 

[starscream5000]

Nice Doward . I've already read up on people's fitment issues with the bigger spearco replica. The fact that the only Issue is relocating the oil cooler isn't even an issue with me since I'll be doing a B&M cooler... You got a complete list of parts on your oil cooler setup? I'll check out your build thread when I get home from work tonight .

 

[Doward]

1 $35 Summit oil relocation kit - SUM-G4985
1 $60 B&M 24 row SuperCooler - BMM-70273
14' of Aeroquip AQP hose - AER-FCN1020 - now, summit wants like $74 for 20' - I got 14' from Big Sun Hydraulic in Ocala for $2.20/ft (it was some they had left over, and they wanted to get rid of it ) If nowhere else, do no scrimp on the hose used. Yes, you will spend more - but I assure you, it is WORTH IT.
1 $40 Permacool Oil Thermostat - PRM-1070

Now, how you go about it is up to you - you'll notice that everything except the actual relocation kit is 1/2" NPT - I drilled/tapped the 3/8" NPT holes and made them 1/2" NPT on the Summit Relocation Kit. I'm also running -10an (5/8) lines everywhere, for full flow.

You can get 3/8" NPT to -10AN adapters, so you don't need to drill/tap - it was just me taking an extra step for full flow Things like this keep me up at night :3d_frown:

You'll need to map out where you want everything to go, then determine the fittings you will need. Figure probably $50-$75 in fittings

 

[starscream5000]

Not a bad deal really, under 300.00 bucks. That's pretty good condsidering the shit they try to sell on ebay for 400.00 and up .

 

[Doward]

And I have to say, it is completely worth it!

I now have greater cooling capacity, easier to do an oil (filter) change, holds about 7 quarts now, as well as increased my oil pressure 5psi @ idle (now idle @ ~12-14psi @ 650rpm)

Also, I've noticed my oil pressure gauge is a HELL of a lot more responsive! Now when I rev the engine, I can watch the oil pressure shoot up to just over 40psi, and let off the gas - comes right back down. I cruise 2k rpm with ~37psi fully warmed up.

This is all on 5w30 btw. Definitely one of the best investments I've made!