Cams.. Discussion, which may lead to a cheap group buy

[Babalouie]

All,

I would take the numbers with a grain of salt. The poweer curves and their relationships to each other are probably pretty good. I seriously doubt that an NA6 donk could do 180hp (130kw ish) without alot more work than mine has. I mean the stock one is 125hp (93kw)! I could tweak the graphs around a bit to be more faithful to the real numbers, but we are more interested in the relationship between the various stages of development and their peak points.

The MX5-845C-Stock and MX5-Stock-Stock models were standard NA6 head flow and induction, 9.4:1 compression and HP Headers with mufflers. The variation was the camshaft specs.

The MX5-845C-Ported is my NA6 with a ported head, stock induction, 10.5:1 compression, small tube headers with open mufflers. This effectively replicates the setup of my car.

The head flows are as measured on a flow bench test of my head when I had it worked.

The induction is 165cfm, as published on solomiata for the 1.6 flapper door AFM.

HP headers and mufflers replicate the stock MX5 'extractors' and exhaust system.

If we assume that the curves are for flywheel hp then I guess it's about right for the non-ported curves. The cams get 12hp which I guess is about 5-6rwkw which is about right for a cam upgrade.

Not sure about the massive gain when the head is ported tho...maybe it just assumes that the fuelling will be perfect, and that the intake/exhaust/header will have enough flow to keep up with the head...and if that's the case then 180 flywheel hp would be about 95rwkw which is about right for a fully modded motor with cams?

[Matty]

Dyno2000 is a bit crude, especialy when it comes to 4-cyl engines. it also has no facility for the actual profile of the cam, rather than just the event timings and lift... still, it's not a bad program.

[adamjp]

I agree with Matty.

Dyno2000 is quite crude for multi-cam, multi valve engines. It is really designed for good old american engines. 5000cc+, pushrod, two valve per cylinder, one in, one out - like god intended. Technology is when you have an electronic oil pressure guage and not a mechanical one.

I would like to upgrade to Sport Compact, but I want to spend the $$$ elsewhere - like on some cams.

2000 is good enough for this kind of what-if theorising.

And Babalouie is right - flywheel HP, not rwkw. One metric horse (kw) is equal to 1.34 imperial horses (hp).

The major difference for the MX5-845C-Ported is port flow, compression, exhaust system. Only bit that is the same is the inlet tract, not much else.

[maxwolfie]

Considering I have a 2" exhaust with standard headers, would you guys say that it would be restrictive (Obviously will be , but restrictive enough to not bother with cams until I get some decent flow out.. i.e. 4-1 extractors and 2 1/4 throughout??

[adamjp]

IMHO your best hp for dollar will be in the form of extractors and 2.25inch free flowing exhaust system.

This will still set you back around $800 fitted, or $1k with ceramic coated extractors. I really recommend the ceramic coating - reduces under bonnet temps a great deal.

[Babalouie]

IMHO your best hp for dollar will be in the form of extractors and 2.25inch free flowing exhaust system.

This will still set you back around $800 fitted, or $1k with ceramic coated extractors. I really recommend the ceramic coating - reduces under bonnet temps a great deal.

I reckon you're right, a bigger system and extractors would make the cams work better but do you reckon he'd still see a rewarding gain with his current setup? Woulda thought so if it was a good system with good bends...

Only one way to find out, Maxie

[Sean]

Horsepower and torque will always cross at 5252. By the looks of the posted dyno graph the numbers are BS.

horsepower = torque X rpm / 5252

torque = horsepower X 5252 / rpm

http://www.carcraft.com/techarticles/868/

It is not a dyno sheet he has posted, but a computer sim...
As such dyno rules do not apply.

[adamjp]

The gain from the cams alone would be much as indicated on the sim graph ~ 7kw. Cams seem to cost around $1k for new billets, less for regrinds.

The extractors will produce that kind of gain with an expenditure of around $500 (ceramic coated), $300 in plain steel.

The 2" exhaust should be fine, particularly if the mufflers are 'open' flow. When compared with a 2.25" system, the 2" will optimise performance through most of the range, just impeding performance a bit over the 6k rpm level. We are talking 1600cc here, not 2000cc. The 845C cams are probably not most suitable in this case, perhaps 805C-NT or similar may be better to optimise performance in the lower rpm ranges.

IMHO the use of mandrel bends on 2.25 or bigger exhaust systems for the 1600 engine will not deliver any appreciable increase in the power gained from the system. The reduction in flow volume through the narrower bends probably won't be noticed too much because the engine just isn't pumping enough gas.

I suppose I am trying to say that for most use, below 6500rpm, a mandrel 2" would be better than any 2.25" system, mandrel or not.

[MxJadeMonkey]

shut up maxie you smell haha haha. whats crackin boys i'mmmm back but still no car yet!!

[Sean]

My new cams should be in and running by the end of this week

[adamjp]

Cool, what have you got?

[Sean]

Cool, what have you got?

Very close to standard basically chasing earlier spool rather than overall power figures, not really any use for NA engines.

Will scan spec sheet and results after tuning.

[tasroadster]

Is there a group buy yet ?
If so.......what costs are involved?

Thanks

[maxwolfie]

The gain from the cams alone would be much as indicated on the sim graph ~ 7kw. Cams seem to cost around $1k for new billets, less for regrinds.

The extractors will produce that kind of gain with an expenditure of around $500 (ceramic coated), $300 in plain steel.

The 2" exhaust should be fine, particularly if the mufflers are 'open' flow. When compared with a 2.25" system, the 2" will optimise performance through most of the range, just impeding performance a bit over the 6k rpm level. We are talking 1600cc here, not 2000cc. The 845C cams are probably not most suitable in this case, perhaps 805C-NT or similar may be better to optimise performance in the lower rpm ranges.

IMHO the use of mandrel bends on 2.25 or bigger exhaust systems for the 1600 engine will not deliver any appreciable increase in the power gained from the system. The reduction in flow volume through the narrower bends probably won't be noticed too much because the engine just isn't pumping enough gas.

I suppose I am trying to say that for most use, below 6500rpm, a mandrel 2" would be better than any 2.25" system, mandrel or not.

Thanks for that... However going with a mild cam such as the 805C-NT - Would there be any REAL (i.e. worthwhile) improvement.. ?

@tasroadster: not yet

[Babalouie]

Thanks for that... However going with a mild cam such as the 805C-NT - Would there be any REAL (i.e. worthwhile) improvement.. ?

@tasroadster: not yet

You'll pick up say 5rwkw, and it'll open up a lot at the top end. But basically it will be the same sort of gain as say, adding headers and a zorst. The main benefit IMHO is that it "rounds out" the powerband, and makes the motor into the engine it should always have been...but it isn't a super-dramatic change by any means.