807-13 Renault crossflow header

[RonPNW]

I'm starting the planning process for completing the install of the crossflow engine in my 70 S2. It's a modified 807-13 from an R17-TS the has and has run with two DCOE 45 carbs. It currently uses the factory cast iron exhaust manifold that fits the S2 frame with no problem. I'm temped to keep the cast iron since it would be quieter, looks like a fairly efficient design and is done but  ....

How much am am I giving up by not going to an equal length bent tube header? Am I correct that the cast iron part will be quieter? Has anyone used the stock cast iron part?

Thanx
Ron

[BDA]

Tubular headers are supposed to be a bit more noisy than cast iron exhaust but I can't say that I've noticed a whole lot of difference after they've been installed on a car. At the same time, I don't think I've noticed the performance difference that I know they provide. I think the choice of muffler makes a bigger difference in the sound of the engine.

Speaking for myself, I'd prefer a sports car with a sporty exhaust even if there wasn't a performance and weight advantage.

[MRN I J]

another thread about this some time ago http://www.lotuseuropa.org/LotusForum/index.php?topic=4200.msg45307#msg45307

[jbcollier]

Cast iron manifolds can be quite a bit quieter depending on head and cam used.  Equal length, tubular manifolds can give you gains bit they can also give you losses.  Could you post a photo of the exhaust manifold?

[GavinT]

. . . It's a modified 807-13 from an R17-TS the has and has run with two DCOE 45 carbs.

In my part of the world (Australia), the R17-TS came with an EFI 1605cc 844-xx engine running 10.25 compression.

When I first installed my mild (too mild, dammit!) 807 engine (late 70's), it was with twin Weber 40 DCOE's but utilising the stock R16-TS cast iron exhaust manifold where the outlet kinda awkwardly faces the wrong way.
If memory serves, the 844 / R17-TS manifold incorporates short primaries and exits as a pair to a twin tubular steel down-pipe arrangement, so that's probably better. Not sure if yours is the same.

Later on when I installed a full 4-2-1 tubular header, it did 'wake the engine up', as the saying goes.
I can't recall if the cast manifold was quieter or not, but that seems to be the conventional wisdom. In any case, I don't remember a night & day difference and the exhaust was noisy in any event.

It's probably impossible to say how much you might be giving up, but it could be argued that improving the inlet and not the exhaust is leaving something on the table.
But given that you're at the planning stage, the exhaust could be tackled later if needed.

[RonPNW]

I may have the engine number wrong and need to check but it was originally a fuel injected R17 that the original owner converted to webers. It seemed to run OK but that was a while ago and I am assuming all the worst until proven otherwise. The manifold is as described for the 844-xx engine. It seems a fairly nice design which is why I asked. I have not taken it off yet. It is likely I'll spend my time and effort on other areas, just give the cast iron minimal tweaks if there is some unsightly internal flash or crap.

I have converted other cars to headers and have always found them to be much noisier than the cast iron manifold (yes, with the original exhaust, which I eventually swapped out). That may be due to the use of fairly thin wall tubing, It is likely a thick wall header would be quieter.

Pics are attached.

Thanx

[jbcollier]

A nice 4-2-1 system can be great for the street.  An equal length 4-1 has a happy place and unhappy places.  In the old days you set everything up so all your ducks were in a row.  The intake lengths and the exhaust primary lengths were designed to harmonize at a certain rpm.  Makes for a big hit but also a narrow hit.  Now, depending on the application, resonating frequencies are not matched to spread things around.  You may not get as high but you will get a broader, more useable power-band.

The R17-TS and R17G came in a variety of specs depending on where and when it was sold.  Up to '74 (?) we got injected 807-13s (1565, 10.25:1, with a smattering of pollution gear).  Other places, 807-12s (similar, no pollution).  Later they came with 844s.

[jbcollier]

I like that design.  It should give a nice spread of torque.  I think it fits because you have a space-frame chassis.  I don't think it would fit, without mods, in the stock chassis.

Having fit lots of tubular headers in my 35 years, cast-iron is definitely quieter.

[Richard48Y]

Not as nice as some of the Alfa Romeo Spider manifolds but should be decent.
Tube headers would get a few more HP and need not be louder.
I have tube headers on my truck in an effort to help mileage, no noticeable increase in noise with my mufflers and long tail pipes.

[GavinT]

Thanks for the pics, Ron.
Your manifold is as I recall them and not too bad, I'd think.

On the engine numbers thing, The Euro spec. 844 as delivered to Oz has different mounting holes from the 821 & 697 such that the OEM Lotus steel L shaped engine mounting brackets don't fit. Not a deal breaker - I made up some new brackets.

Agree with JB re the differences between a 4-2-1 system and a 4-1.
But in practice for the home gamer like most of us here? Mostly we follow the well trodden path of what works. If building a dedicated race engine, you'll probably try all manner of options with dyno data to back up the decision making.

But the principal still holds true.
In practice, my 4-2-1 system with a mild cam, 1565cc low compression 807 engine was, I thought, pretty reasonable.
My mates 4-1 system on his 1647cc low compression engine using a R17-TS cam and 45DCOE's displayed quite different characterises. With that car, you could start off from rest, hold the throttle at a fixed position and when it reached a certain RPM, the car accelerated all by itself as it came onto the cam.

But there's other factors as well that cloud the situation. I found the change to even my mild crossflow engine showed a marked increase in torque over the old 1470cc engine, so I reckon any loss of torque at the low end doesn't amount to much in the real world . . at least for a Europa.
Indeed, I recall starts in hill climb events meant you couldn't take your hand off the gear stick because, if you did, you didn't have enough time to get it back there for the change to second.

Crikey, I can ramble . . .

[RonPNW]

Thanx guys, I really do appreciate the feedback.
Looks like I'll keep the iron and focus on other issues (ignition, water pump, trans, and did I mention that every piece of rubber in the car needs to be replaced?).
I agree, as cast manifolds go, this one does look very nice, In particular having a rather long section before the final collector. I'm sure there is some horsepower to be found in this area. I hope to explore that once I get the car on the road.   And now, back to rebuilding the wireing harness.

Thanx