2g SMIM causing power restriction?

[Wicked95AWD]

I had my car dyno tuned this summer and at the time I was using a 62mm Accufab throttle body a single rewired walbro 255 and 880cc injectors with a ported 2g mani and an internally gated scm6152e on my built 2.4 motor. I made 345whp and 340ft/lbs of torque on pump gas at a measley 17lbs of boost.

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The shop owner didn't want to turn up the boost any higher because it was so hot at the time he was afraid it would detonate badly. Since my numbers were lower than I wanted I decided to go all out and upgrade to a setup capable of huge numbers. I added a second inline fuel pump, 1200cc injectors, a Q45 throttle body, a divided t4 tubular header, a tial BOV, tial 44mm wastegate, and an HX40 pro turbo. I'm just about ready to throw the car back on the dyno but I'm considering swappping my 2G SMIM for a 1G model with larger runners before I do my go-for-broke 600+whp or bust run on race gas and I need suggestions. My car has a 2g head with stock valves as well as FP dual valve springs and FP3 cams. I have a 2g Magnus intake Manifold and i've been told that the small runners of a 2g smim is a big restriction vs a 1g SMIM at high boost levels. Of course, I have also read that the port angle and velocity of the 2g head is better than the 1g head despite the smaller intake ports. Would I be better off to swap to a 1g head or can I simply modify my 2g head to accept a 1G SMIM and have the best of both worlds...high flow and superior port angle/velocity?

 

[Jeff@Slowboy]

There is a big controversy about what head is better. The way I see it, the 2g head is more efficient in the face that it has a better entry angle and more port velocity. On the other hand there comes a point where you make the transition from "how efficiently can I get this air into the combustion chamber" to "how much air can I fit through this port". In short, I prefer the 2g head for street/strip weekend warriors because o the better low end and mid-range characteristics and I prefer the 1g head for the all out balls-to-the-wall large frame turbo monsters. Im sure there will be a lot of argument over my opinion because there are so many ways to look at it and a lot of variables to account for. I hope this give you a little insight to help you with your choice.

Oliver
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[Wicked95AWD]

SMIM = sheet metal intake manifold. Stock 1Gs and 2Gs have intake manifolds, not SMIMs.

Look at JMFAB, JM Fabrications for SMIMs.

I'm not really sure why you just defined what a SMIM is. I know what a sheet metal intake manifold is.. I have one.. it's a 2g magnus. Did you read my post?

 

[DGajre777]

I'm not really sure why you just defined what a SMIM is. I know what a sheet metal intake manifold is.. I have one.. it's a 2g magnus. Did you read my post?

I glanced at it and posted in a hurry. My apologies, I deleted my post.

The 1G vs 2G head "fight" has been going on forever. You could just get a 1G head with JM Fabrications or JM Fabrications and call it a day.

 

[Wicked95AWD]

No worries.. honest mistake. So, If i get a SMIM designed for a 1g with larger runners and gasket match the ports on my 2g head to fit, does that completely negate the port angle and velocity advantage inherent in the 2g head?

 

[Jeff@Slowboy]

No worries.. honest mistake. So, If i get a SMIM designed for a 1g with larger runners and gasket match the ports on my 2g head to fit, does that completely negate the port angle and velocity advantage inherent in the 2g head?

Short answer is yes. Reason being is that you are essentially turning it into a 1g head when you do that. Will it lose all of the 2g qualities? probably not, but it will likely lose some of the important ones. Any time you port/polish/gasket match anything you are changing the efficiency aspect, wether it be positive or negative, if you are dead set on larger ports just build a 1g head. Its all about volumetric efficiency.

Oliver
[email protected]

 

[Wicked95AWD]

Do you think it would be worth the investment to gasket match the intake ports on my existing 2g head to fit a 1G SMIM as well as add 1mm oversize valves and port/polish the whole thing (Polk Performance quoted me around $1,200) or could I get similar results by simply transferring my existing cams and dual valve springs into a used unported 1g head with stock valves?