Big cam 304 Tuning help needed

[Vrv8hz]

G'day all. I have been tasked with the job of trying to make a badly built motor drivable. The motor is a stock VR 304 with auto which has had a h304 cam fitted I am told by a couple of lads in the shed. I have looked up the species online and it is a big angry cam that requires 10:1 comp, which it does not have.

I'm told by the owner that the expectation is that the car sounds tough, clearly performance is not going to be a thing.

I was not around for the fitting of the cam so I have to assume that it is degreed correctly, but i cant say i am confident either.

I was able to get the car to run well enough to drive the other month but now I'm attempting to improve it and that's proving frustrating.

The car is running a 424 and I have started from the stock 11p tune. I have only tuned my own turbo cars to this point so going off a few posts about big cams wanting more timing down low and at idle I was surprised that this motor only stopped backfiring and carrying on under any load when I halved the stock timing map. Fueling has also been tricky as the wideband does not seem to show anything richer than 14:1 no matter what I do. I can get it to run rough but it does not seem to display rich. Could be the sensor but it has been running fine on my car previously.

Before beginning I checked fuel pump pressure, base timing, plugs, ignition module function against a known good unit, checked firing order, checked map sensor against a known good unit, checked tps function, replaced the stock dirty injectors with a fresh cleaned set of L67 injectors that I adjusted the tune to suit.

Most of the cam tunes I have found on here don't seem to be as big as the h304 from what I read.

Hoping that there are some ideas out there to get this pig rolling down the road.

[Vrv8hz]

Screenshot_20250110-172453_Samsung Internet.jpg (134.89 KiB) Viewed 365 times

[vlad01]

Can you post up some specs? I have a pretty good understanding of tuning cams of all sorts and getting far from ideal combos to work alright, so I should be able to assist.

I was actually going to do a big write up and guide on cranking/cold/warm/hot starting and warmup for cams as I found some very counter intuitive results that go against 99% of the advice and hearsay on the net. But my health limits me to smaller stints of being able to do anything really involved at the moment and likely for some time, it's on the list but I can't promise anything for a universal guide write up.


EDIT: You just added the specs as I posted this

[Kevspec]

Thats a 286 not a 304 won't be hard to make it right for what it is obviously needs more comp etc but would need at least valve springs and correct length pushrods and convertor. As for fueling make sure injectors are big enough as factory definitely won't be aswell as the fuel pump. Besides that it's just timing playing to get correct.

[seabreeze]

I am almost finished tuning my VN 304. Crow Cam 226/232, .505/523 112lsa. Not as big a cam as the H304, but a step or two smaller.

It starts cold or hot, idles smoothly and is almost stealth! Stock shorty headers, stock cat and 2-1/2 single exhaust. I have flatops 0.040 over, 10:1 comp, rebuilt heads and a 2500 converter. Drives easily with no hesitation or bucking.

I think i started with Dylan's 284/286? tune from here and that was a great starting point. I may have copied parts of the timing map from the VR 288 Final tune too. I think i was rich pretty much everywhere with a few lean spikes with Dylan's tune. Liked more timing at and around idle too. I remember the biggest single improvement was getting iac steps to around 15-20. Everything seemed to flow nicely after that. It happily idles at 1000rpm and 850rpm in drive. I still have a ways to go with my VE and timing maps. They are not as nice a looking graph as many tunes here!

It is my first build and tune though. Many of the settings, especially with regards to cranking and idle, were taken from threads here and tweaked. I'm sure those who have tuned dozens of combos, with actual "big" cams can speak with more authority. I couldn't even get tunerpro working to begin with, so make of that what you will.

[Vrv8hz]

Thanks for the replys.

The cam specs are just a quick google, I'm going off the owner advising that the cam is a H304 so perhaps the google specs were wrong.

Is overlap going to be the cause of the lean afr readings? It seems pretty severe but I don't have any experience with tuning cams so maybe that is it.

I'll have a go at getting it to idle happy with as much vac as possible then road test afr in the midrange and smudge a bridge between.

If I can get a log worth reading I'll put it up for you guys to take a look at.

[VK_3800]

Unless the tune is way, way off what you've described sounds like there is still some other problem that needs fixing rather than being purely the fault of the cam. More compression would definitely be nice but it's only slightly bigger than the popular 286 which will basically run in anything; certainly shouldn't be causing issues like backfiring.

I have early heads and 10:1 compression with a 242/252@.050 cam (albeit wider lobe separation at 112). It ran fine on $12P other than some minor surging at low rpm cruise (manual with solid clutch doesn't help). The biggest issues I had with tuning were more to do with the cold air intake mucking up the charge temp.

Lean readings can happen with significant overlap at low rpm but should improve quickly when driving; personally I've never seen a huge error. As you say tuning the idle with vacuum would be a good start if you don't trust the wideband.

[vlad01]

That cam should be reasonably tame to dial in for the idle, start up etc...

Counter to popular opinion, the wider the LSA, the harder to tune and more picky it is with precise fueling and needs to be much leaner even though the idle is smoother once dialed in, tighter LSA is far more forgiving and easier to tune but ultimately runs rougher when everything is done and dusted. LSA is one of these things that must be calculated for the engine before being made, wide makes a lazy engine, tight gets the most of the combo for the given cam size for most engines. 110 is decent though and a LOT better than those wide ones like 112 or higher.

110 is basically in the middle of the two extremes but leaning towards what most engines actually want which is generally 110 to 106 range.

[Vrv8hz]

Thank you GM for putting the coil in the best possible position. I imagine that's why when the owner said that they had checked out everything before I came along... they had not checked the coil.
Running better with a dusty old coil from the parts shelf and actually responding to timing like it should. Still not much afr info to go by but a big step forward.

[Charlescrown]

I moved my coil onto the inner guard and used a longer coil lead. That spot was a real afterthought.