CFM Rating?

interex · 09-27-2008, 05:39 AM

Okay so I'll try to explain myself real well so you can understand what I'm trying to figure out.

I have a 2G, bored .040 over (86mm) and it's a 2.3 Stroker. I have a Stage VI SBR head, 1mm over manley valves, crower 280 cams, and a JMFab clone, custom intake manifold. I've not got a turbo yet but I am looking at something like a HTA-35R, or T4Z, or GT37R, or equivalent. I am really trying to figure out my CFM Rating so I know which throttle body to buy. I've spoke with a guy at Holley, and MSD and they both told me their 90mm is rated for 1050-1150 CFM. I'm not too good with math, and measurements so I know I won't be able to get this info myself.

Can someone please help me figure out what my CFM rating would be so I can pick out a TB that will be perfect for my engine. And NO I'm not interested in a Q45 TB, I've found several local to me for $50 but I'm not interested.

Thanks.

xxShaneOmac · 09-27-2008, 07:05 AM

Are you sure they are not talking about CFM of your turbo?

Like how much air your turbo will be pushing through the TB?

Id think pre TB matters more then Post TB.

delta448 · 09-27-2008, 08:33 AM

I'm assuming the numbers you got from Holley and MSD were for V-8, naturally aspirated, LSx type applications. When you introduce forced induction into the equation the CFM rating of a TB doesn't matter as much. Anyway, a 90mm TB is huge and will not be much of a bottleneck IMO. How much bigger can you really go anyways? 90mm is a little more than 3.5".

interex · 09-27-2008, 01:01 PM

I'm not exactly sure how you measure the difference when introducing forced induction. I just want to make sure I buy the right TB for my application. If a LSx type 90mm TB will work then that is what I'll buy. If I need 75/80/85 mm TB then that is what I'll buy. No need in having something I cant use properly.

95GSXracer · 09-30-2008, 02:53 AM

Many people have had excellent success on those turbos with a stock 60mm throttle body. That being said, 75mm is a typical upgrade size, for reference. Most aftermarket SMIMs can be bought with a 75mm flange.

interex · 09-30-2008, 06:21 AM

Well, I want to make sure I am going to buy the right size. I don't want to spend the money and then end up needing smaller, or bigger.

dsm-onster · 10-02-2008, 07:51 AM

Bigger gives more throttle response and guarantees more flow potential, so you really don't have to worry about making the wrong decision. I would go for the most bolton friendly and affordable setup. Like the 75mm TB upgrade.

interex · 10-12-2008, 07:10 AM

Thank you much.

twicks69 · 10-12-2008, 04:38 PM

If your intake manifold is already flanged for a 70 or 75mm throttle body, then take advantage of it.

Otherwise, a 1G 60mm throttle body is more than plenty for any of the turbos that you have mentioned.

andy4g63 · 10-12-2008, 05:17 PM

Yep and there is a good read on Buschur foru
Random FMIC information with a little turbo info mixed in..... - Buschur Forums

I know it is mostly about FMIC, but somewhere along the way was their testing of 75mmTB and 3" UICP and they made less power and more lag. Turbotrix's built white Evo went 9.2 on a stock 60MM TB and this guy above me Twicks69, went 9.9 on a full weight 2G with a 60mm TB and made 740WHP.

interex · 10-17-2008, 05:21 AM

Very nice, thank you for the information! I think I'll actually test a 70mm bbk and a 75mm msd. I have a buddy who has both who said I could try them when I get my setup done and which ever works best he'll sell rather cheap. My manifold is already flanged for a 75mm TB but I feel I can make a thin adapter plate I can use if I need to go smaller.

twicks69 · 10-17-2008, 11:06 AM

Good luck!

andy4g63 · 10-17-2008, 11:06 AM

Check the following link, JMF has an adapter from 75mm BBK to stock TB.
JM Fabrications

Look under DSM flanges.

interex · 10-17-2008, 04:44 PM

I could make that in no time for much less than $61.00 Hell I bet I have an aluminum drop about that size sitting in the shop now. I'll see about cutting one up on Monday and seeing what I can come up with.

I do work in a machine shop, which is where my intake manifold was made. (JMF clone to exact specs).
My buddy does some awesome work with a TIG!

I thank you guys for your input, very helpful.

pboglio · 10-17-2008, 06:16 PM

Here's a throttlebody calculator:

REVTRONIX - Throttle Body Calculator

Hope this helps.

interex · 10-17-2008, 06:35 PM

I greatly appreciate it but I have no idea how to even use that. Short of calling myself ignorant... but I'm not very smart when it comes to measuring air, velocity, and displacements etc... :P

pboglio · 10-17-2008, 07:13 PM

Click on the pressure down arrow and turn the units to psi, then add whatever psi you want to run plus 14.7 psi. So say you want to run 25.3 psi on your boost gage, just type in 40 psi in the cell. Then just select 2.0 liters and the rpm where your max power will occur, say 7000 rpms. Switch the number of throttlebody bores to 1, type in the diameter of your throttlebody plate, 60mm for a stock DSM. And then select calculate at the very bottom. It'll basically tell you what your theoretical horsepower will be WITHOUT the throttlebody restriction, but it will tell you what your horsepower LOSS will be. Then keep playing around with throttlebody diameters to see what kind of power you'll gain by swapping bigger.

I don't know, I found it to be pretty stupid simple to use.

interex · 10-17-2008, 07:43 PM

I understand that much, but the Air temp, and Volumetric Efficiency I'm lost about, but I do understand it in theory and have played with the calculator a bit.