3 inch single exhaust - power limit ?

Mark · Post by **Mark** » Sun Dec 14, 2014 9:41 am

I'm building a 331ci - 5.4 small block Ford powered Sierra and have a Cosworth 3" stainless steel system.

Headers are home made 4 into 1 with 1 5/8" primaries and 2 1/2" collectors.

Plan is to connect both the headers to a single system.

10:1 compression, Edelbrock performer RPM heads and EFI intake

30 lbs/hour injectors

Roller cam not bought yet.

Hoping for 350bhp +

Is the 3" system going to be OK?

Looking on American forums I need 3 1/2 inch

kiwicar · Post by **kiwicar** » Sun Dec 14, 2014 1:16 pm

Hi
Ideally you would want a 2 1/4 collector with a single 3" system and 1 5/8 primaries. 2 1/2 will slow the flow in the secondaries just to speed it up again in the single 3" pipe and this causes back pressure and kills any scavenging. A single 3" system is plenty big enough for 350 BHP.
best regards
Mike

Mark · Post by **Mark** » Sun Dec 14, 2014 1:56 pm

I'm stuck with the collector size now

2 1/2" seemed to be the default size when I was looking for collectors

It's all welded up now, so not much I can do about it...

DEVONMAN · Post by **DEVONMAN** » Sun Dec 14, 2014 5:15 pm

Slightly off topic but I'd be interested to know what mods were involved to get that T56 into the sierra. ( Tunnel etc) It's on my list of things to do and any pointers would be great. Currently I have a T5 behind a 4.6 twin turbo motor.

Regards Denis

Mark · Post by **Mark** » Sun Dec 14, 2014 6:30 pm

T56 went in fairly easily.

The main problem was around the home brew bell housing, I had to give the transmission tunnel a good beating with a club hammer to get it to clear - no cutting required though.

Other than that there is plenty of room in the stock tunnel, mine is a Mk2 and I think the tunnels are bigger compared to Mk1.

Pic of one of the headers finished, the 2 1/2" collectors don't look too far out of scale to me.

Would going up to a 3 1/2" system counteract any problems caused by the large collectors ?

kiwicar · Post by **kiwicar** » Sun Dec 14, 2014 7:51 pm

Hi
yes 3 1/2 would be pretty well ideal for 2X2 1/2 collectors. Within about 1% of perfect.
best regards
Mike

Mark · Post by **Mark** » Sun Dec 14, 2014 8:40 pm

Thanks Mike.

So it's simply about cross sectional area ?

2 x 2.5" is 9.8 square inches

1 x 3" is 7 square inches

1 x 3 1/2" is 9.6 square inches

I'm not sure how it all works as there is only going to be one bank firing at a time

Looks like I'm going to be making a 3 1/2 inch system

stevieturbo · Post by **stevieturbo** » Sun Dec 14, 2014 9:00 pm

Collectors arent as straightforward as you'd think..or maybe they're just surprising

Many favour a merge style, where the collector does narrow down, before opening up again into the main system, so the drop to 2.5" wont be a problem.

https://www.youtube.com/watch?v=NekTRPx68zs

And 3" would be no problem at all at 350bhp. Whilst not a direct comparison, I've seen over 700hp on a 2.3 turbocharged engine with a very quiet exhaust, ie 2 large 3" silencers and single 3" the entire way.
n/a is slightly different though, and sizing a bit more important

youtube is good for searching all sorts of info these days. There were other good collector videos I seen, but cant seem to find them.

stevieturbo · Post by **stevieturbo** » Sun Dec 14, 2014 9:08 pm

Not sure how a Sierra tunnel compares to a MK2 Granada

But the T56 fitted into mine fairly easily too. I just removed the original gearbox mount that went up and over the tunnel. Like a second skin about 3-4" wide that created the mount.
Then welded up some new mounts

Although I had already done this for the R154 Supra box anyway. So a little trimming of some lugs off the T56 and it was an easy swap.

It is a big box, and it is a tight fit. But certainly not a difficult one.

Mark · Post by **Mark** » Sun Dec 14, 2014 9:32 pm

stevieturbo wrote:
It is a big box, and it is a tight fit. But certainly not a difficult one.

It is a heavy bastard though

Edit to add I did use a merge cone if that makes a difference ?

stevieturbo · Post by **stevieturbo** » Sun Dec 14, 2014 10:17 pm

Not sure about the cone, or how critical it is...or size of cone.

The top end collectors have that cone formed as part of the bends they cut to form the collector, so it's an integral part, rather than a weld on afterwards part.

But from the videos, the taper and "merge" then open up seems to make a good difference. As to how much it affects power, I'm sure that's a huge variable too, as with tube lengths, diameters etc etc.

Just boost it and never worry about all that

lol

DEVONMAN · Post by **DEVONMAN** » Mon Dec 15, 2014 9:46 am

Mark,
Thanks for the gearbox pics. Looks good.
It looks like next summer's project on my Son's sierra will be a t56 implant.

I already have a T56 in my hot rod with a Mcleod slide on concentric clutch throw out bearing. I've had a few leak problems with this item so be warned. They include a spare set of seals when you buy it so that sort of tells you something.

Regards Denis

kiwicar · Post by **kiwicar** » Mon Dec 15, 2014 7:02 pm

Hi
simply put yes you aim for constant sectional area, but take the ID not the OD. Stevie is right about the merge collectors. . . but for higher tune engines, with 350 BHP it is really just a case of getting the gasses out, and what you have looks good, you don't have enough overlap on the cam to worry about it.
best regards
Mike

Mark · Post by **Mark** » Mon Dec 15, 2014 8:54 pm

Thanks for the replies

I'll see what mood I'm in when I finally get to sorting the exhaust system!

I've heard plenty of bad things about the Mcleod bearing, Real Steel assured me they are great

How did you stop yours from leaking ?

DEVONMAN · Post by **DEVONMAN** » Tue Dec 16, 2014 9:38 am

Mark wrote:Thanks for the replies

I'll see what mood I'm in when I finally get to sorting the exhaust system!

I've heard plenty of bad things about the Mcleod bearing, Real Steel assured me they are great

How did you stop yours from leaking ?

I put new seals in twice now and at the moment it's holding up ok. Fingers crossed. In my car the engine and box has to come out as a unit to do the job so it's not a quick fix.