building an intake manifold, input needed

[sharkey]

ive decided its time to build my own intake. ive been tossing this idea around for a while now and with no real gains from everything i did last winter (tranny swap, megasquirt, big tb, some other things) i started looking at my intake and thinking of how little air can be pulled through those 1x1.25" holes between my middle and upper plenum, never mind the 180* corner its gotta flow through.

what im thinking is using 1.5x2" rectangular tubing, bringing it out overtop of the valve covers (much like stock), and then build a plenum, basicly a big box, to bolt to the middle intake. i will be using the 60mm jeep throttle body im running right now, i figure itll flow plenty for what my little 2.8 requires.

any thoughts on runner length??? i know longer is better for low end. i figure i can have the runners 7-8", coupled with the lower intake that ends up around 12-13" to the head. also plenum volume im not quite sure of. depending on runner length, the plenum would end up at 12" wide, 10-12" long, and i figure i have room for 2-2.5" tall. this would end up with a pretty good volume, mabey to much??? also, whats the thoughts on diverters to direct air towards the runners???

any input would he helpful. also, if anyone has built a custom intake, post up some pics, i wouldnt mind having a look.

btw: my motor is a 2.8l ironhead, 9.5:1 compression, comp cam, ported heads, ect.

[1988GTU]

I dont know how much you'll actually gain, but maybe contact boostedrs since he does custom MPFI upper intakes. IMHO forced induction or 3x00 upper end swap is the way to go for the 2.8/3.1MPFI's since they have small lengthy ports.

[john_V63400]

Why not bore the hel out of a stock one and build from there

[Superdave]

Custom is nice but almost all the custom ones i've seen kinda ruined the drivability of the car... there was a few done a couple years back..

maybe swapping over to the 3.4 iron head stuff would yeild better results?

http://www.turboz24.com/Pics/Current_Engine_32.JPG

^^ Sexxy

[sharkey]

the stock middle intake is just tiny, like i said, between the middle and upper intake, the ports are 1.25x1" with no room to realy do more than gasket match. also welding cast aluminum isnt great, id rather start from scratch.

swapping to the 3400 top end is out of the question, id have to change out my forged pistons to make it streetable, as well as i have over 20 hours of porting in the heads alone. i know the heads flow decent, but trying to suck air through that horrible middle/upper intake transision is killing it. from what i have heard, the stock 3.4 intake doesnt flow much better, and i would have to get an external crank trigger and run dis (or ford edis).

now when your trying to cram air down its throat, thats a different story. this is actualy a plan of mine eventualy, however i do want to have a 14 second time slip n/a, and if i can make the intake flow better to feed it n/a, it will also make a big difference with boost.

[Superdave]

with all the work into that engine.. just a 3400 top end would put you into the low 14's easy...

I understand about wanting to keep those heads though.

what about a LIM for a carbbed application, then run a TBI setup on it.. you should be able to find something like that at the junk yard.


Plus you could use a Hilborn scoop then

[DEI37]

Custom is nice but almost all the custom ones i've seen kinda ruined the drivability of the car... there was a few done a couple years back..

maybe swapping over to the 3.4 iron head stuff would yeild better results?

http://www.turboz24.com/Pics/Current_Engine_32.JPG

^^ Sexxy

That is a cool pic. Definitely easier access to the coils rather than the location down on the block under the front exhaust manifold.

[torq455]

isn't that turbo z24's engine?

lets not forget when you split up the UIM and the LIM, the runners are no longer equal length. you can't keep the LIM and say...put a 3500 kind of UIM on. the engine will vibrate a lot! you could extrude hone it and gain smoother walls and more volume.

[sharkey]

i have thought about tbi, even a carb, howerver neither of those will work well with the ultimate goal of turbocharging it. 3400 heads would be great, the biggest issue is the pistons. i would be needing to pull the motor right apart, and have it rebalanced, and basicly be throwing a good set of $700 forged pistons on the shelf. i may aswell just start over with a 3400, something im not willing to do.

i know the heads flow, the intake doesnt. it just doesnt pull as hard as it can up high, itll go 2.0 60' times, but still only runs 15.5 @ 85mph.

[IsaacHayes]

3400 heads and LIM with a 3500 top hat would accomplish basically what you want to do and possibly make more power with the better heads. Sell the motor and build a 3400/3500 combo to swap in with the blower... Then you'll have PLENTY of power. I know, I know, no love for the iron heads...

[torq455]

shift earlier.

[sharkey]

yea no kinding no love for them. you guys can get off the top end swap thing, im not going to do it, and lets get back on topic of building an intake manifold. you guys seem to be forgetting that the 60* putting down the most power is an ironhead.

[1988GTU]

What type of comp cam do you have?

[sharkey]

comp 260h2 and comp magnum 1.6:1 roller tip rockers. and ive tried shifting earlier, as low as 5000rpm. it actualy slowed me down as i drop out of the powerband (starts around 3000rpm) on gearchange.

[bszopi]

I used to have a whole bunch of link from back when I was working on a plenum design for my 3x00. Hopefully someone will be able to chime in, but IIRC, you want to design the plenum volume to be equal to that of the engine volume. And I think that includes the runner volumes as well.

As always, I will post a link to Ben and I's favorite site when it comes to engine theory: http://www.theoldone.com/archive/int...old-design.htm It doesn't really go into too much depth, but gives some things to take into account when designing an intake.