[madhunm]

Hello,

I was looking at the cam timing on the ROCAM 1.6 engine on the Ford TIS and came across this :

At 1mm lift,

intake opens 12 degrees after TDC
intake closes 24 degrees after BDC
exhaust opens 24 degrees before BDC
exhaust closes 12 degrees before TDC

now, using an online cam duration and overlap calculator (here : Camshaft Calculator - Wallace Racing) the result is as below


Your cam has an Overlap of -24.00 degrees and has in Intake Duration of 192.00 degrees.
The Exhaust Duration is 192.00 degrees.
The Inlet Cam has an Installed Centerline of 108.00 degrees ATDC.
The exhaust cam has an Installed Centerline of 108.00 degrees BTDC.



what is the advantage of a negative overlap cam?

any responses appreciated.

thanks,
[SIZE=2]Madhu.[/SIZE}

[im_srini]

Hi Madhu, I'm no engine guy, but it seems that the parameters you've listed indicate that the exhaust closes 12 degrees before TDC while the intake opens 12 degrees after TDC.

So simply, there's no overlap at all !

[ananthkamath]

I doubt that's correct. There can't be negative overlap on a modern engine like the Rocam.

I think its more like:

Originally Posted by madhunm

At 1mm lift,

intake opens 12 degrees before TDC
intake closes 24 degrees after BDC
exhaust opens 24 degrees before BDC
exhaust closes 12 degrees after TDC

[1100D]

Negative overlap is actually power lost. Think Ananth's reply is more like it.

[madhunm]

Hi all,

thanks for replying... the only reason which i can actually think of for an engine to have negative overlap is to avoid flow reversal through the intake.

can the ikon possibly have a poorly designed intake system?

anyway, as far as what ive learnt, more overlap means more air into the engine. hence, more fuel - more power.

negative overlap, as per Cam overlap.... - CamaroZ28.Com Message Board seems to suggest a 'greener' and 'torqey' engine performance. actually, thats no surprise, since trhe ikons torque curve is pretty much flat from 2500RPM till the red line of 6200RPM.

now, ive searched all over for a replaement performance cam, but with little luck.

what is the best suggested overlap/timing for an engine with roller followers? please suggest a profile thats a litte easy on the pocket.

thanks,

Madhu.

[ananthkamath]

Originally Posted by madhunm

At 1mm lift,

intake opens 12 degrees after TDC
intake closes 24 degrees after BDC
exhaust opens 24 degrees before BDC
exhaust closes 12 degrees before TDC

Like a jackass I missed this part completely. Overlap is quoted at zero lift (i.e. advertised duration), not at 1 mm lift. Find the specs for advertised duration for your cam, or measure with degree wheel and then see the overlap.

[madhunm]

Another intresting point to note is this :

there were 3 ROCAM engines developed by ford Brazil.

1.0l Supercharged,
1.3l NA
1.6L NA

for specs, refer Ford Sigma engine - Wikipedia, the free encyclopedia

i may just be fishing here, but the parts may just have carried forth from the 1L engine. we know that the 1.6L rocam is just an overbored 1.3l engine.

i have one question about measuring the overlap myself - do i really ahve to remove the engine out?

anyway, my actual goal is to design a header - ITB combo for this engine which has its 'sweet' spot between 3500 and 4000 RPM.

thanks,
Madhu.

[madhunm]

BUMP!!! any comments on this?

Anyway, I am thinking of installing a BP285 spec cam in my car. Already have a K&N Apollo CAI with the battery re-located, free flow exhaust.

Jitu, your view on this? after the cam upgrade, i intend to install uprated injectors and a standalone ECU (probably RaceDynamics or the megasquirt i have lying around)

My goal is to have a fast NA car before going TC or even SC.

[ananthkamath]

Originally Posted by madhunm

My goal is to have a fast NA car before going TC or even SC.

Originally Posted by madhunm

anyway, my actual goal is to design a header - ITB combo for this engine which has its 'sweet' spot between 3500 and 4000 RPM.

I'm not an expert but in my view these are somewhat mutually exclusive. Unless you have access to some serious equipment and/or ITB's which can take boost. Motorcycle ITB's are unsuitable because they have a thousand unused holes in them which you will have to plug, otherwise you WILL have a major boost/vacuum leak.

For the ROCAM which is an SOHC engine, again in my view, getting a hairy NA cam like a 285 is a bad, bad idea when you eventually go turbo. In addition to losing low end you will make less power on boost due to the high overlap.

Do yourself a favor and get boost. Like Now.

[Ford Rocam]

Hi Madhu,
Dump the Piper 285 Cam, there's a company in S.A which makes bolt on cams for Rocam 1.6 engine & its been tried & tested with dyno results depicting gain on top end with out loosing torque at lower rpm, overall good gains when combined with good intake & headers (4-2-1) with free flow. that too on 9.1 c.r, get a good head job & raise the compression & results will be phenomenal.
Here's the link
Ford Performance Cams | Camshafts | Racing

[madhunm]

Hi Jitu, Ananth,

I did speak to Burnout... by the way, they have a new website : Steve Wyndham Racing

the cams they advertise are conforming to BP285 spec. i am actually in the process of procuring a cam and header set from them.

as regards the head job, i really dont know who to trust... experience or someone with a flowbench. i know Psycho does a head jpb near my house... as does Raj on the other end. some say they advise it and some say they dont.

i am really confused here...

as far as TCing my ikon, im considering moving the brake booster to the passenger side fender, so i have ample space near the firewall. i shall try and post a pic to illustrate what i mean.

[vezj420]

hi Madhu....have you managed to get the cam from SW Racing, South Africa yet?

let me know if you did and what process you had to go through as I am thinking of doing the same soon.

so, you're thinking of TCing your Ikon?? That's quite ambitious...in fact, TOO ambitious for me so I'm staying away!

But do let us know how it goes, eh? It would be interesting to trace your progress.

[hiran77]

Originally Posted by Ford Rocam

Hi Madhu,
Dump the Piper 285 Cam, there's a company in S.A which makes bolt on cams for Rocam 1.6 engine & its been tried & tested with dyno results depicting gain on top end with out loosing torque at lower rpm, overall good gains when combined with good intake & headers (4-2-1) with free flow. that too on 9.1 c.r, get a good head job & raise the compression & results will be phenomenal.
Here's the link
Ford Performance Cams | Camshafts | Racing

Hey Ford rocam,

Can you please let me know if you had installed this cam in your IKON? Also how is the performance gain?? any change in the top speed too?