Which exhaust manifold for best FE? with pics

[GasSavers_Erik]

I am currently doing an FE engine swap- I am replacing a carbed 1987 Honda 1.5 L CVCC 9.2:1 compression ratio with a carbed 1987 Honda CVCC 1.3 liter 10:1 compression ratio (it came stock with this high compression ratio- and there was no recommendation for premium fuel).

So- I have the choice of using the 1.5 liter exhaust manifold (the top on in the pic) or the 1.3 liter manifold.



The 1.5 liter manifold is internally divided into 4 runners for the first 3-4 inches and then each pair converges and finally the two converge just above the cat.

The 1.3 liter manifold is not internally divided so that two ports immediately converge and then of course both sides converge. The area of the 1.3 runners is a little smaller than the 1.5 runners as well.

I would guess that Honda sized the manifolds according to best performance, but which do you think I should install for the best FE?

By the way- the 1.3 liter did not come with an oxygen sensor- hence there is no hole in the manifold for one.


1.3 no internal dividers



1.5 internally divided for the first few inches




Which should I install for FE?

I know the 1.3 will keep the exhaust flow faster because its passages are smaller, but the 1.5 has the internal dividers that may act like mini headers... so it seems almost like a tie- anyone out there ever seen an HF manifold to tell me how Honda designed those? How is the VX manifold set up?

[2000mc]

if theyre interchangeable and from the same year, i would imagine that honda would have looked into this. they also would have saved money by only using 1 manifold on 2 engines. which would seem to point to the idea that honda did look into it, and thought it best to use a different design for each engine. unless you get some good opposing info i'd keep the 1.3 manifold on the 1.3 engine

[VetteOwner]

i dunno but either one clean out the carbon outa em lol

whats the sensor bung for in the top one?

[dkjones96]

I like the 1.3L manifold and would personally choose that one.

[Philip1]

if you have no plans to spin the engine fast I would use the manifold with the smaller runners. it will help move your power band down.

[GasSavers_Erik]

97% of the time the engine will be under 3K rpms- thanks guys- 3 votes for the 1.3 manifold, 0 for the 1.5

The bung hole in the 1.5 is for the oxygen sensor (I have an extender installed in the manifold right now)

[dkjones96]

Gotta love those electronically controlled carbs! I knew Toyota did that but not Honda.

[GasSavers_GasUser]

The 1.3l manifold looks more free flowing from the pic. It was also made for that motor so I would think it would be the one to use in my opinion.

[jeep45238]

If the runners are the same dia and approximately the same length, I'll take the divided runner one any day of the week.

[GasSavers_Erik]

Originally Posted by dkjones96

Gotta love those electronically controlled carbs! I knew Toyota did that but not Honda.

Actually the carb is very simple- the only wires going to it are for the choke heater and the idle shut off solenoid (anti dieseling solenoid).

Honda controlled the mixture by using a bunch of valves that create a controlled vacuum leak. I have been fiddling with this system to lean it out as much as possible.