Pontiac V8 custom intake

[Sprockets]

Hi guys, not sure if this is the correct forum to post this, but wanting to call upon the collective knowledge of "Team VEMS"!

Currently in the process of buying a (don't laugh) 1977 pontiac firebird trans-am fitted with the proper 400CI pontiac engine, and I'm already planning the EFI conversion   The big problem comes with the intake manifold choice.  Seems the common way is to buy what equates to a big single single plane manifold with injector bungs machined in, and top it off with a 4 barrel throtlle body of some sorts.  Just thinking though, if this is the best way for a large V8, was thinking along the lines of an ITB set-up on a home brew cross ram manifold with 4 48mm DCOE style throttle bodies, trying to keep the intake angle as straight as possible.  This way, I get a true individual runner setup rather than what equates to a large plenum.  Seeing as I want to run a relatively wild cam (I plan on using it basically as a road going drag car) I can see the single plane giving me issues.  Or am I just over complicating things?  If it was all out drag car, I would just go with the tried and tested setup.  I'd even go as far as just using a carb! But this car also has to pass emissions and be able to at least drive to town and back every now and again.

Besides the intake probelm, everything else is quite simplistic.  8xLS2 'yukon' coils, 36-1 trigger on the crank damper, and either butcher the dizzy to turn it into cam sync, or if i still have space probs, machine it right down to leave the drive in place and mount a phase sensor on the timing chain cover.

Other issue I've considered is a way to manufacture a smooth rectangular to round port transition.  Thinking of making a tool to use in a press to form the rectangular part into the round tubing.

Any thoughts/comments/suggestions to get a proper engine welcomed lol.

Cheers,

-Gavin

* As a quick edit, after some more googling and general research trawling through a lot of my book shelf, I really wish I had paid more attention when I was doing physics lol.  I'm now trying to wrap my head around various equations which will more than likely be of no use to man nor beast, but it's making interesting reading.  As I have cheap dyno time available, I think this may be a fun thing to play with.  Also, dnb, I keep looking at your rover manifold and it keeps my mental gears working!!  Seeing as I haven't got the car yet, gives me lots of thinking time, where maybe I should just make something that my gut says looks right and give it a whirl! *

[dnb]

There's nothing much wrong with old 2 valve per cylinder puhsrod engines.   Specially when they have enough CIs.  (Mine's a mere 302 )

I found that fairly big isolated runners worked well for me on the intake.  They are grouped such that 4 go to each plenum and there is always 180 crank degrees between intake events on each plenum - this has significantly reduced charge robbing from the original Rover plenum.  And because there are still plenums that see vacuum there, the engine is still more-or-less tractable in traffic unlike some of the 8 TB engines I've seen.  (OK, some 8 TB engines are just fantastic, but they tend to be based on flat plane cranks like the TVR AJP8)

Sizing the runners is quite a critical thing - I expect mine isn't yet optimal, mainly because I haven't played much due to killing the diff and clutch.   The plenums and manifold only gained 53 bhp - a bit short of the 70 I was aiming at.

You don't need camsync, but it would be nice to have.   However I'm sure you already know this...

[Sprockets]

Thanks for your input dnb, was hoping you'd give me the low down on your manifold design

One question, I assume you are running the original injector positioning?  This is where I may come unstuck in the IR setup, with the injector being placed in the far end of the runner.  Good for power, but ldle quality may be reduced, but thats not such a big deal.

Your intake design would be a simpler fabrication process for me, and would also allow closer injector placement.  Something for me to ponder about.  Seeing as your intake would be simpler (and cheaper!), this may be the first design, then a second IR setup designed and made to do some back to back testing.  I can always sell one or the other lol.

One problem I have tho is with the dyno testing.  Being an auto box will struggle to get power curves on a chassis dyno.  Will have to investigate engine dyno time when both intakes are designed, or maybe fit a manual shift body to the box and engage the torque converter clutch to give me a reading.  Not really my ideal, as I want to keep the auto feature, but hardly a major problem. (I'm gonna upgrade to a TH200R4, not the strongest of choices, but a cheap way to install a 4 speed auto box!)

There is one thing though dnb, I'm envious of your engines weight, thats why I need the extra 100 CI's lol.  They do make an aluminium block and heads tho...but thats a long way in the future, with the stroker kit...well....be rude not to lol.

Cheers!

-Gavin

[dnb]

Yes, I'm using the standard near-port injector position.  I wouldn't worry too much about the injectors being a long way away from the port.  It works in the AJP8 after all...

Can you not peg the car in one of the "overtaking" gears?  Or does it not have them?  I am ignorant of automatics since I have never driven one, let alone owned one.  (Will change in Jan when I get the Rangie )

I wouldn't be too envious of the Rover v8 - at least until you see the poor head design.  350bhp is about the limit for a 5 litre engine unless you want a full-on race cam and all the headaches that go with it.