First I'd like to say the information on this forum is amazing. I'm pretty new to TBI and tuning- just getting into it. Basically I've run into a roadblock in my engine buildup. I put together a nice 383 forged crank, aluminum fastburn type heads- (flow well 256in @.600 192@600 ex) Comp Cam 260XFI, Stainless 1 3/4 to 3" headers into single 3" exhaust w/highflow cat, 255lph fuel pump, and I bought a 54mm TBI unit from dctrumpet. I was wanting to use the stock intake (because of emmisions) and bore it out but did not realize it could only be bored to 49.5 mm. Anyway the question here is will a 49.5mm aka 2" bored unit with a 1" spacer have enough flow? If not I'll have to get a carb unit and adapter plate, and change it out along with the tune every time registration comes. What do you guys think. Remember this is all brand new stuff I've purchased so I'd like to get it right the first time. From what I've read the edelbrock tbi intake really isn't much better than stock.

 

Welcome to TGO

Well, as you have said so yourself there is a lot of information out there. The 2" bore is actually 50.8mm. 54mm is just a hair over 2-1/8" (2.126). So what you have to build is an adapter plate - funnel that narrows down from 54mm to match your bored out intake 49.5mm bores (1.95").

Based on 260XFI specs (I hope you have good springs) it is designed for 1200-5200 RPM range - Stock BBC TB can support 640CFM which is from air flow perspective should be enough to support your 383. The minor narrowing due to intake manifold may hurt the high RPM end, but it would make for a very nice mid range performance. The issue will be fuel support - talk to Sean (aka DCtrumpet) he can get your setup going in the right direction. As for emissions you can forget about going with a carb intake (in Cali it will not fly), but it maybe enough to get by where you are.

//RF

 

Fuel support should be fine. I have a 255LPH fuel pump, 18 psi spring, and 90# injectors. One thing I did not notice for intakes was the GM ZZ4 intake- it has egr and I beleive it flows as well or better than a edelbrock performer rpm, I could use an adapter plate for the 54mm Tbody. Also Holley's 300-66 projection intake has 2" bores already- anyone tried boring that out. I don't have one to look at up close unfortunately however pictures of it appear to have a flate top with no water jacket near the bores. Also both would require relocating the egr valve and possible use of an egr spacer, anyone succefully used one of these and re plumbed the egr?

 

JDUBB

You can use 300-66 since it supports conventional EGR valve. I used 300-49 (for pre-86 heads) on several of my conversions.



Boring Holley intake is possible, but it would leave very little material for back retaining bolts to 'bite' into. Unfortunately, I did not measure bore diameter when this photo was taken. IRC it was over two inches but I do not recall by how much. This was taken over three years ago.

On your fuel - with a pair of 90# at 18 PSI your engine should support 400HP. The problem is going to be idle - you may want seriously to consider VRFPR.

Also, if you are running 700R4 you'll have to be creative with TV cable bracket. At least three years ago there was no clean solution (bracket) offered by Holley since I had to use 1" spacer to clear TB fuel lines:




//RF

 

Thanks for the detailed pictures. I see the problem with the bore /hole edge margin, and the clearance issues for the fuel lines because the base is located farther forward on the Holley. It will probably be easier to run the stock intake with a 1" spacer or so. I'm not looking to get an incredible top end rush anyway. I want power to about 5500 rpm so it sounds like the stock intake will work fine bored with a spacer (what do you guys think?). As for the vfpr that throws another spin on things I'll probably have to invest in that too.

 

I would rather bore and port match the 3704 TBI performer then the stock intake.
They can be found used for cheap.