Tip to tail exhaust redo

[jagonza]

I have a 77,with all a smog equipment removed, and a 4-1 stock exhaust. I have sourced a 1608 4-2-1 exhaust manifold and a new center and rear exhaust section,.

My question is on the down pipe, I have seen two different styles for sale , not sure which one I should get , the earlier or the later version of four bolt down pipes. I believe the 4-2-1 came from a 1608. Can anyone tell me the difference between down pipes. I know the fuel,injected ones are different, but I don't know the difference between the early carb versions.

The PO did quite a bit of work, ~10:1 compression, heads, cams and carbs, I am hoping this is the "last touch", from an engine stand point.

Any tips on any part of the exhaust work is greatly appreciated.

[carl]

You might want to talk to the guys at Auto Ricambi. I know that the later downpipes are longer and allow you to use this type of exhaust on a 2L. I also know that some manifolds and downpipe have noticeably smaller diameter pipes at the joint of the manifold and downpipe but I don't know what years are the smaller version.

[So Cal Mark]

don't expect any huge improvement by just mixing and matching stock components

[jagonza]

So Cal,

Really not looking for much of a performance improvement, more of an aesthetic improvement, I am very happy with the way the PO built up the engine, it already has more power than the greasy 13in tires can handle. : )

I have looked at your headers and may give you a call down the road.

Now if only i could find an old school carb expert !

[Nanonevol]

Do you have the original carb or was that also upgraded?

[jagonza]

The carb is the ADFA , freshly rebuilt.

[jagonza]

Finished my redo - early 4-2-1 , AR downpipe - AR Peformance center and rear mufflers (resonators ?) .

So how is it, well all i can say is how it feels - the low end seems to have lost a bit of umpf but wow it's a different car above 5000 rpm, it will rev to redline like never before. i always thought it had trouble breathing at high rpm, but i guess it was more of an exhasut issue, really revs free and easy now.

BTW i found this in a german forum on spider - i have included the google translation. the guy measured the difference between early and later 4-2-1 and found the early had 27% larger passages - measured by filling with water and measuring.

"""Today I measured 2 pieces of original Fiat manifolds twincam and came to the conclusion that No. 4151276 2 has 27% more volume compared with manifold 4,166,429 4.Anyway, the No. 4151276 2 following data (note only the volume is good, measured the other measurements were / are harder to do) Volume of water in manifold 778 ml primärhål diameter 42 mm sekundärhål diameter 37 mm compared with manifold 4,166,429 4. Volume of water the manifold 613 ml primärhål diameter 38 mm sekundärhål diameter 32.5 mm manifold No. 4,151,276 2 is also designed a little differently than No. 4,166,429 4. however, it is difficult to measure but an estimate is that No. 4151276 2 mounted on the motor will be shifted 15 mm more to the right and about 15mm more downward compared with the manifold No. 4,166,429 4. manifold No. 4151276 2 manifold No. 4166429 4 cf. manifold No. 4166429 4 and manifold No. 4,151,276 2. Conclusion: with 27% more volume can be manifold No. 4151276 2 probably give a power increase cf. with the manifold No. 4166429 4th

[Nanonevol]

This is a topic I had looked into a bit. See:
http://www.fiatspider.com/f15/viewtopic.php?f=5&t=30080
My approach was different, simply measuring the openings. I would concur though that the difference appears to be significant.

[So Cal Mark]

merely measuring the volume doesn't take the runner length into consideration. The best way to compare would be to flow test each manifold