Exhaust manifold thoughts?

[Torby]

Guys,

I'm in the process of rebuilding my engine. Well, rebuild and tune. L24 stroker, medium street cam, triples etc. Now I've been looking and looking at exhaust manifolds, but can't decide what to go for.

When I look at the cheaper type headers, they all seem to bend down quickly right after exiting the exhaust port, if you know what I mean. Now, I know next to nothing about designing headers, but from my point of view, the cheaper headers are designed so that the exhaust gases will hit a 90 degree bend right after exiting the port. Surely, this can't be good for power?

Imho, I think the header should have a smoother bend before the collector, to make the exhaust gases flow better to the collector.

Please educate me on this!

 

[status]

i have a 3.1 with a nismo header mated to GDS system,GDS are in Notingham Eng;and i think

 

[SeanDezart]

Yours is LH or rh drive ?

Lhd can compromise the shape due to the steering column.......more proof that our cars were designed to be Rhd !

Email me - I might have something for you.

 

[Rob Gaskin]

Status, GDS are in Brackley, Northamptonshire. I was very happy with my GDS system apart from constant problems getting a gas seal at the head.

2.4 Stroker - what is that then? Is it a 2.4 with 2.8 crank, standard bore?

 

[morbias]

Wouldn't that make it an L26? (assuming L26/L28 rods)

 

[rallymanDP]

Torby, to answer your question more directly, the 90 degree bends straight after the ports are of course necessary to clear the Carbs and Inner Wings, if that is what I understand that you are describing.

Apart from that, the most important aspect of Exhaust Manifolds on tuned 'L' Series Engines is the length of the secondary pipes after the bottom 'Y' piece. If they don't go back as far as the Gearbox area, then ( in the case of the cheaper variety with a 6-into-1 design ), they will produce a flat spot at around 4,000rpm which many of us on here have discovered to their annoyance.

The DJS.30 ones are about the best value available on the Market at the moment - not cheap, but then the best never is, and will help to produce the sort of power that you should expect from the mods that you have done. Also available in LHD format if that is what you have.

 

[status]

Rob,i knew it began with an n,never had any problems with mine even before we put the Nismo on

 

[Rob Gaskin]

.......... the most important aspect of Exhaust Manifolds on tuned 'L' Series Engines is the length of the secondary pipes after the bottom 'Y' piece. If they don't go back as far as the Gearbox area, then ( in the case of the cheaper variety with a 6-into-1 design ), they will produce a flat spot at around 4,000rpm which many of us on here have discovered to their annoyance.

My GDS system did go back a long way but the problem was that it was one piece until after the 'Y' , so to change the box or clutch I had to remove the exhaust manifold with also meant I removed the carbs. This made the job a lot longer than it should have been. So worth bearing that in mind when choosing.

 

[status]

Fourways also do a copy of the nismo if i remember correctly and cheaper than some others,i think,worth a look

 

[rallymanDP]

The Fourways ones that I have seen ( and bought not long ago ) were nowhere near a copy of the NISMO ones - more like the Janspeed version.
Worked very well all the same.

 

[Torby]

Thanks all for your input! Much appreciated!

I'm aware of the clearance issues, I was just thinking that the cheaper type headers I've seen so far could have been improved, at least just a little.

Anyway, yes my car is LHD, and it's a L24 with a stroked L28 crank. It will be slightly bored, just waiting for a set of pistons now. Stuck with the L24 with the intention of keeping "matched numbers" (yeah, I know this doesn't mean much on the Z's). That plan went down the drain however, due to a completely rotten chassis, so the engine is going into another Z. L28's aren't plentiful in my neck of the woods.

I wasn't aware of the secondary pipe issue, that is indeed good info for a newbie like myself. The djs30 manifold and exhaust looks extremely well made!

I've tried to the best of my abilities to do good research, and chose the "right" parts so far, and I'm fully aware that quality costs a lot. I might as well rename the car "money pit", but so could we all I guess.

Thanks a lot for your input!

 

[status]

Im going back about 6 years or so Duncan,they may not be as good now,i also had an MSA complete system that mr f got me,it sounded a bit ****** at first but just got better the older it got and the engine was breathing better than it did with the Janspeed,ive had a few different exhaust syatems and i still say the gds is the best ive had so far

 

[Ian Patmore]

Torby,
Add to the mix... you also have to get the exhaust header primaries right as well. Too big a dia. and the gases the engine produces will slow down (as to fill the "extra" pipe dia) and power will be lost. For me, with your mild tune, don't go too big a dia. Surprised no one has mentioned it yet, as there has been plenty of discussion in the past.....

Mild to wild 2.4's and mild 2.8's work well with a 1 3/8 whilst wild 2.8's up need 1 3/4 primaries.