The Edelbrock TBI 3704 intake manifold comes with smaller 42mm bores than the O.E. TBI intake 46mm, does not have the crossflow bore between the two bores and has some little details that appear can be improved.

I used this intake with enlarged 47mm bores on a LO3 with LT1 cam + all supporting moods and then on the DIY 360 TBI, it worked well.

Recently I had the engine apart due to an oil pressure issue, I then decided to do some major porting to the 3704 intake manifold before I put it back on.

First of I increased the ID of the bore to around 48mm and made the crossflow hole about 1 in. x 1.4 in. in oval form.






The porting bit measures around 0.47 in. D x 1 in. tall.




Edit: here is a pick of the stock TBI intake manifold bores, that I posted many years ago

https://www.thirdgen.org/forums/atta...lo3-intake.jpg

 

I wish Edelbrock had cast their TBI performer intakes like they did their performer TBI-MPFI conversion intakes. They were small plenum single planes.

Check out this aspect of porting the intakes. I noticed the same thing on my 3704 when I had it. Cleaning up the ports really helped for me.

 

Yes that is exactly what I did, then I removed the bump on on the lower radius and grinded off a lot meterial off the walls on the plenum sides.

 

The top radius was just straightened and smoothed to the rest.

Overall I removed a lot of material from this intake manifold.

 

It looks like you are getting there. I think the reason these manifold runners flow so unevenly is due to the differences in runner shape, location and dimensions. Once they are all cleaned up, it makes a huge difference.

Are your heads setup to run the 1204 or 1205 gaskets? My 081 TPI heads were brought out to the 1204 size and I opened up to a 1205 on my 187s.

 

Not sure, I used the stock replacement FEL-PRO MS93317 as template, I then put the engine back together and used Victor Reinz MS15401, this time I did not want any blue gaskets on my engine.

The engine has the Summitracing 170 cylinder heads http://www.summitracing.com/parts/SUM-162108/ the intake ports https://www.thirdgen.org/forums/atta...7966-122ko.jpg are slightly bigger then the ones of the intake gaskets.

And here how it runs https://www.thirdgen.org/forums/tbi/...imple-fun.html



Edit:

One detail I forgot to mention is the bottom of the bores (red arrows), I spent a lot of time to chamfer the edged as much as possible with the tools I had, particularly the deep one.

 

Hey there thomas quick question, how big is that crossflow hole? How did the port job end up working on the car?

Thanks!

 

My car is not a race car so this works good enough. Crossflow hole is about 1 in. x 1.4 in. in oval form, it made a noticeable positive difference. I would do it again.
Off course if stock look is not required, there are certainly better intake manifolds out there.

 

had no idea this manifold had 42mm bores, thanks for posting

 

Dude that manifold can be bored to 50mm all day long. I know this for a fact

 

50mm is 2" right or close to it?

 

Yes
1" = 25,4 mm

 

2.54 cm; 25mm