270/280 degree 8V cam on std inlet do-able?

[u33db]

Can anyone tell me if it likely an 8v cam of circa 278-280 degrees duration will work on a std inlet manifold if the std setup is about 230 degrees?

I'm not really to sure as it seems an extreme increase as the engine powerband would get bumped up by 2k rpm...

Thoughts?

[BenR]

The less efficient the form of carburetion, the more rpm you will have to pull to make power and the narrower the power band.

[kj16v]

I've never put a 270+ cam on a injected car, but I've read that the engine management won't like it and'll cause it to idle lumpy.

[stan]

The rough idle is inherent with long duration cams due to increased overlap. on closed throttle u get exhaust gas dilution/reversion due to partial vacuum across exhst valve around tdc...esp at low engine speeds where gas speed is low. this causes rough idle...but can be ironed out with decent mapping.

i have 285deg cams on my t.b engine, and it idles spot-on 900rpm...exhaust sounds noise...burbles up an down/on-off kinda thing like a rally car, but the actual speed is spot on. benefits of prgrammable ecu and non-std inlet tho.

[BenR]

I find the biggest problem isnt the flow reversal but on cars running speed density setup, the manifold pressure fluctuations really play havoc with what the ECU is 'seeing' the engine do. As far as the ECU is concerned, the high-low-high-low manifold pressures can trick the ECU into thinking its actually in a throttle open state, and will either cut idle strategy or close the ISCV etc.

[u33db]

Well this is the setup it'd be on;





From what you're all saying it seems a bit of an unknown but likely to have problems - should i just try it and see?

For obvious reasons this is just a cheapish project so if i can keep as much of the original setup it's much better but, i have issues on the std inlet and std ECU (albeit with alter rev limit), what will be the 100% cast iron way of sorting things out;

- different ECU with std inlet?
- different ECU with different inlet?
- piggyback ECU (dastek or similar)?

If i std inlet is a no-no how cheap and what'd be involved in going to carbs?

[stan]

I find the biggest problem isnt the flow reversal but on cars running speed density setup, the manifold pressure fluctuations really play havoc with what the ECU is 'seeing' the engine do. As far as the ECU is concerned, the high-low-high-low manifold pressures can trick the ECU into thinking its actually in a throttle open state, and will either cut idle strategy or close the ISCV etc.

Aye this is why i would try and avoid MAP on NA applications.

U could try it, and depending how *bad* it is, either put up with it or move onto a different managment set-up. all depends how far u want to got, and how much u want to spend.

[u33db]

In regard to how *bad* it'd be - do you think it just idle roughly (ie. that sort of 'wub-wub' type sound) or completely fail to idle and stall? I can put up with a lot of roughness as the car is flat out all the time anyway just not stalling if i step of the throttle in traffic...

[stew]

In regard to how *bad* it'd be - do you think it just idle roughly (ie. that sort of 'wub-wub' type sound) or completely fail to idle and stall? I can put up with a lot of roughness as the car is flat out all the time anyway just not stalling if i step of the throttle in traffic...

whats the point for what looks like a 1.2???

[u33db]

Errr....group 2 insurance/300mile to a tank/relaibility/simple to work on and repair plus being a laugh!