Mod'd 930's, What size Header primaries?
 

Hello,
For you folks that have mod'd your 930's. What diameter of Primaries are you using on your headers?

i am in the process of making my own headers utilizing Burns collectors. I will be going with 1 5/8" primaries. i want to keep the velocity up. I have read that 1 3/4" to 1 7/8" is too big for a 3.3 to 3.6L motors... if anyone else has an opinion.... let it out. I am at the stage of ordering material.... So, still open for changes....

Design to application is crucial. Too big and lose velocity as stated.
Another design issue is primary length and symmetry. This is also critical to efficiency. Very few headers have equal length primaries.

What are your goals, specifically?

I had a well-know "tuner" tell one of my customers that 1.5" primaries were too small for his 400HP application. I sent him a picture of a 600HP engine using the same exchangers.
LOTS of BS out there. Find an unbiased expert who builds successful systems without being tied to the manufacturer giving the best discount. Goran (beepbeep) comes to mind.

Hi,
I have some cracks in mine, I believe they are 1 5/8". Since some new ones may be in my future, I was just wondering what diameters most are using.

My car made 5 to the tire on a 12 year-old set of bolt-on B&B's that were modified for a T-4 flange. I dont know, mabye I should go bigger...

I use 1 5/8 headers on an EFI car. If it were CIS, I would stick with stock. I also have equal length headers, but would recommend short pipes for mostly street driving. The most important part of my pipes is the waste gate circuit and how efficient it is.

Mine are 1 3/4 equal length headers with twin tial 44mm wastegates. This is the most responsive, and best flowing setup for a single turbo car. With a large single turbo the single pipe is not the best design. Granted this setup is overkill for most, but looks killer anyway:)http://forums.pelicanparts.com/uploa...1224463601.jpg

Bigguns

http://www.rudtnersracing.com/Mike/Mikesheaders.gif

1 3/4

Expected peak power/torque range of the motor, and overall power output(expectations/goal) really are needed to determine what primary size to use.

In lamens terms......how much power you want to make and where in the rpm band you want to make it most. There are so many variables in the final decision it cannot really be laid out here easily.

Example: Eg33 motor going in my 962 kit car-------> 3.3L(96.9mm B/75mm S), GT3582R .78AR twin scroll, sequential meth injection ~500whp 1-3/4 primaries into 3-1 merge collectors into 2" parallel up pipes to turbo volutes(TS flange). Making peak power on this setup around 4600rpm(redline 7200)

Realistically on a street car response and torque is what you'd want and a smaller primary(all else equal) is better for that. :)

This is why the application must be well considered before jumping in. The aftermarket does not offer too many variations on header design. All work but none are optimal for every street application. The compromise, as always, is weather an expensive custom system will return the investment when a mass produced product will suffice.
Bigger is definitely not better. 1 3/4" primaries reduce velocity, the function of which is a square of tubing diameter.

Exactly, 100%.

This is why 90% of my business in designing and fabricating headers and intake manifolds revolves around very specific setups. IE, I'd build an intake manifold based on a particular engines' comp ratio, rpm range used(or expected gain area), specific camshaft lift and duration, port sizing, etc, etc. Flow vs velocity and reversion characteristics make the job tedious.

Same theory applies to header design. In any effect, even a smaller runner header, if designed right, can and will flow very very well up top and not sacrifice low end torque or response.