thoughts on custom roller cam

[delcowizzid]

hey guys just had our turbo ground cam arrive in the post from my cam guy.want to see what you think of the specs and see if anyone has anything similar.its to suit LN3 i think our aussie and newzealand 1988 3800 is in our commodores.its for the vb drag car engine fully stock 3800 8:1 or 8.5:1 comp ,log style diy manifolds, super T70 china special turbo 0.84 hot 0.70 cold 3" single shot from turbo to tip only hotdog style resonators X2 not real mufflers,42Lb high impedance injectors ,2bar map sensor ,3" cooler pipework and 300x600x76 front mount cooler runs 14psi at the moment boost will be going up at a later date.3.45:1 diff gears and locked diff with T5 manual box.so far car has done 12.6@109mph.cam guru says expect 10-20% gain in HP with the cam.that added with extra timing that we still have up our sleave should grunt it up a bit.cam card is attached how does it compare to cams you guys use.its a reground factory cam had a good tickle up increased duration and lift 0 overlap

thanks guys any input welcome

cheers MIKE

 

[ijames]

I'm not a big cam expert but to me those lobes look a lot milder than are common here on the 109 block 86-87 turbo 3.8. Typical valve lifts are about .500" with 1.55 rockers and more like 210-212 degrees duration at 0.050". Bigger durations may not be ground with much more lift but they get to that 0.5" just as quick (0.5ish lift is where valve-piston and retainer-guide clearances all have to be checked carefully and even ported most iron heads don't pick up much more flow past about .5 or .55" lift). Especially in "milder" builds up to maybe 500 rwhp the rpms are kept below about 6000 since the stock crank flexes and so does the block. Somewhere in the 450-500 whp range people start adding billet main caps or a girdle or a forged steel crank (yes, lots have gone way, way past that with stock bottom end but this is where some builders start to beef the bottom to reliably get the rpms up to 62-6500 ). We make the power with boost, not rpm, and this means that differences between camshafts are pretty small and it is rare to see a big difference from just a cam change. Even up to maybe 700 rwhp with a stock block the peak rpm is (my guess from watching lots of TSM races) within 500 rpm of 6500. With an efficient T70 turbo and front mount and about 18-20 degrees advance at WOT you can run 20-24 psi boost on 93 octane pump gas, and with alky or race gas 25-27 psi is pretty common, with as much timing as the octane will stand up to about 25-26 degrees. Obviously you need a 3 bar map sensor, and I think your 42 lb/hr injectors will be your next limit. I'd go straight to the high impedance 60's. Good luck with it all!

 

[delcowizzid]

cheers for the reply mate
got the cam to open up the topend a touch since we wind it out to 6000-6500 way past the stock N/A cams range factory rev limiter was around 5400-5600 if that for N/A and the cam falls over way before that.60Lb seimens are on the cards for the next installment will be making an engine for boost when we cant go any faster or start breaking things.lots of the guys over this way fit GN turbo rods and pistons in these engines then get the crank mallory heavy metal balanced which costs a lot.so far we havnt even blown a stock graphite head gakset @ 14psi on a fully stock 200000km+ N/A engine never opened.runs 95 octane day in day out i think our 95 is measured different to yours we have 91 95 and 98 on the pump and its tuned for 95. this time shes getting a tank of avgas from the airport for tuning for the strip and will have a tune for the street for 95 pump gas.at the moment its only running 13 degrees total timing at 14psi no knock plenty more in it yet

 

[delcowizzid]

shes alive fired up for the first time today after we got it all setup.shes definately in need of some tuning was rich as smoking really black smoke at idle.will throw the wideband in tomorrow and begin tweaking the tune again wont take long to dial in the idle and get out on the street for cruise tuning low load areas.got a nice idle not that lopey being 0 overlap but the duration has given it a slight chop definately doesnt sound stock wait and see what sort of vacuam its pulling at idle will be the decider

 

[KL Mallender]

lol, overlap is where the "chop" comes from, dont forget that your valves are opening and closing at the "advertised" duration numbers not the at .050 numbers. good luck.

Kevin.

 

[delcowizzid]

struggled for 3 days to try get it tuned swapped so many parts then found the issue 1 injector stuck open and burnt out and i dont think the others are much better.its allways been odd since these injectors went in never ran right at cruise would go 5 cylinder then as soon as you got any load on the engine would go 6 straight away think he injectors were on the way out when we got them they were supposidly brandnew of a company on ebay .so now have 60lb seimens deka high impedance ones on the way so we can get back to tuning

 

[ijames]

Glad you caught the injector problem without melting a piston, that's usually how they get found. Let us know how the tuning goes.