VK 308 realy flat

[kane_coro]

Hi all,
Have just run in my rebuilt 308 finally.Took it for agood long drive last weekend and wasnt very happy with how it goes when you give it shit.If you put your foot down its very flat until about 4500 5000 rpm.If you ease your foot into it its not as bad. Im thinking fuel problems...
Any one got any helpful hints??

Its a 308 30 thou over with flat tops,edelbrock torker manifold,holley 600 vacuum secs.HEI dizzy.A mild cam but im not sure of specs on it.Pacemakers and 2 inch duals into a three inch tail pipe.

[the_boozer]

are the secondrys opening as soon as you flaten it are they working bigger jets ?

[MY_84_VK]

Yeah, check to make sure the carby is functioning properly and you're fuel mix is right, could even be jetted wrong? Another problem might be air leaking into the manifold somewhere, I had that problem with my worked 202 when I first built it, turned out the extractors were leaking air into the gaskets.

[kane_coro]

The secondarys should be working,the carbs new.How do you tell if they are opening when they should?The jets havent been touched i just bought a new carb and dropped it ont there.Shouldnt be any air leaks its got new gaskets everywhere.

[ari666]

.How do you tell if they are opening when they should?

put a paperclip on the opening shaft about half way up take it for a drive and give it half throttle. when you pull over the paper clip should still be there. also if you can see them opening when the car is stationary, then they are probably too loose.

so you bedded in the cam and are 'running in' the engine? or did you slap it together and take it for a spin?

whats the timing set on?

[VK SL 3800]

If its a fresh engine give it some time to run in, some engines dont loosen up for a few thousand k's

[kane_coro]

What do you mean by the opening shaft?Engine is run in.It has done about 1800km.Timing is set to factory, about 6 degrees form memory

[Reaper]

did you get the dizzy regraphed to suit the new cam/carb combo??

Reaper

[ari666]

cant find a decent pic. anyway, under the bit with the pink splotch on it is a shaft that connects to the secondarys flap and opens it. put the paperclip on the middle of it.

6 degrees is way too little. 12 would be a good starting point. that will make tonnes of difference.

edit: the shaft will look like this:


you just cant see all the rubber crap cos it is in the assembly.

[kane_coro]

Oh ok I thought that was what you meant Ari.I wil try adjust timing tonight if the rain stays away.From memory it started pinging with much more advance though.
Reaper na i didnt, i guess thats a specialist type thing to get done??I live in the wops

[ari666]

you can diy the springs (inside the dizzy) but you need to know exactly what cam is in it. i am guessing its something pretty tall though if you are using a torker manifold.

are you using ported, full or manifold vacuum for vacuum advance? i have enough pics to do a write-up on changing the springs, if you want to have a shot of doing it yourself. but you need to know how heavy or light you need them. so cam specs are very necessary.

[kane_coro]

Haha the torker is only on it because it was all i could get my hands on quickly to suit the heads i have.I had worked heads originally but the hardened valve seats started leaking water so had to go back to standard heads which my original manfiold didnt suit.Im unsure of cam specs.Motor came in lots of pieces,cam was new but not in a box so dont know what it is..
Im using ported vacuum off the carb for the vacuum advance

[ari666]

yeah ported is right, everything else 'will do' it shouldnt be 'flat'. ill bet it was pinging cos' the engine is still a bit too tight. you have to give it a real good pounding so the rings can bed before itll spin around properley. which may be why it could only handle 6 deg. but seriously you should be running twice that. and itll make a huge difference on power.

[Guzzoline addict]

The problem is probably the torker manifold having low air speed and making the carby run lean, which in turn is making it so you cant advance the timing.

[ari666]

yeah i was wondering that too, but assuming the block is zero decked and he is running 56cc chambers, he should have up to 11:1 which keeps the torker happy.

[kane_coro]

Guzzoline addict if the problem was the torker leaning out the mixture can you put bigger jets in the carb to over come this??
Ari, i got a chance to play around tonight.Timing was set to 8degrees.I put the timing up to 12degrees and it pinged like ####,went really well but pinged really bad so I knocked it back to 10degrees.Still pings if you snap throttle wide open but goes better than it was.What do you mean by zero decked?Is 56cc chambers the standard head size?Sorry if these are stupid questions but this is all new to me,First motor i've built.

[ari666]

ok, well if it is pinging even slightly then you need to set it back to 8. pinging is REALLY bad for your engine.

sounds like there is too much comp for that dizzy. try using a heat range colder plug in the meantime. but you need to get your timing curve tightened up.

[RazzaCaine]

sounds like your having similar issues to my 308. i cant run it on anything higher than 6 degrees otherwise it pings

[kane_coro]

Ok will try get some colder plugs for it next week then maybe Ill have to send it off to get dyno tuned...

[ari666]

look, in all honesty, colder plugs helped me get 2 more degrees of timing in, so its a bit of a band-aid for a broken arm really. you need to tighten up the curve. what rpm does it start pinging at? mine started at 3200 when i was trying 14 degrees. at 12 degrees it was around 4000rpm. then on the fwy at 3000 rpm (which is 100kmph with my diff) it would rattle under slight throttle until around 3700 then stop.

basically the vac advance curve and the mechanical curve need to work together, otherwise a stock dizzy with a high comp engine will mean that mechanical starts at 2800 and vac advance will kick in its 12 degrees as soon as you get a bit of vacuum, which will mean pinging. as another temporary fix i tried disconnecting the vac advance which worked perfectly and allowed me to run 11 degrees with 5 heat rang spark plugs, but the problem i then faced was any time i sat on the freeway for more than 15 mins the car would overheat, due to no vacuum advance.

one 'bush mechanic' thing i was going to try was locking the mechanical advance altogether and just running with the stock vac advance module. which would mean you can get good base timing AND have your vac advance to keep temps down, but you will lose quite a lot of advance at high revs, which will give you lots more power.

so in the end i bought one of these: CHEV -Monaro - MSD Advance Kit - GM HEI - P/N #8428 | eBay

which dont fit perfectly with my dizzy, but they work with a little tinkering. i used the heaviest springs in there which means mechanical starts to come on at 3300. INSTANTLY able to dial in more initial timing with no pinging at all.

sadly i only got to play with it for about 3 or 4 days, then i reversed the VK over a giant concrete lump and ripped out my exhaust. but everything was running sweet till that point.

hope that helps

[kane_coro]

At 10degrees mine was low,maybe 2000 - 2500rpm then would go away.Lower temp plugs have made it better.Nearly all gone.Unfortunately its WOF time now and i need to start focussing on my rust issues so i can be legal again.Hit the bubbles on driver sill with a grinder and amazingly theres holes underneath.Take off the guard and wow theres more under that.Im guessing itl be the same story on the other side, and around the rear screen.And possibly the front screen,and maybe behind the wiper motor.......Why do i spend my time and money on the VK instead of my VX?????

[ari666]

Why do i spend my time and money on the VK instead of my VX?????

you are asking the wrong guy, man...

*shakes head*

[kane_coro]

At least im not the only perverted guy around Ari.
I was thniking yesterday with the 12 grand (Wishful thinking) ive spent on the VK in the last two years i could have turbod or super charged my SS and had money left to spend on my ute.Over twice the power with no rust issues, better go,better handling better stopping.What am i doing.Hahaha
Lucky i have beer to keep me positive

[kane_coro]

Got around to sorting flat spots and timing issues properly yesterday.Took the VK down to my nearest dyno tuning centre.They put it on and it put out 123.8kw and 631nm torque at the wheels.Was leaning out something wicked though.They went up two jet sizes on primary side of carb (could of even gone up one more they reckon) and they replaced the advance spring inside dizzy.
It now makes 132 kw and 677 nm torque which I thought wasnt to bad for something with small valve heads and no head work at all.

[ari666]

wow man! thats not bad at all! you just gotta get it to rev a bit higher and then your laughing.

suggestion:
ditch holley and go back to quaddy. get it setup for your cam. i guarantee it wont lean out like it did on that run.
roller rockers. even though they do bugger all, they 'free up' your revs a bit by having a poofteenth less fiction. also YT's add x0.05 lift for free.


but otherwise looks like a nice and flat power curve to me. be nice if it could just follow that line up to 5000rpm