What can a machinist do to VMax heads for more power

[dij0674]

Hey All,


My machinist says he can shave the heads and decrease the combustion chamber, and increase the compression ratio. Any ideas as to how this will effect Torque or HP. What else I can do to VMax heads to squeeze some more juice out of them? Port? Polish? Any dyno numbers on some worked heads?

Damien

 

[[email protected]]

I've never seen any dyno results after head work. Check out the PCW website for ideas on what can be done. I've heard you can have issues getting the exhaust lined up if you shave off too much.

 

[dannymax]

Never been a big fan of beefing up the top end without doing the lower end too.

+1 on PCW, these guys have a long history of building performance v max engines....be worthwhile to check them out.

 

[dij0674]

Thanks for the advice. I'm currently doing a full rebuild of the engine, I've done the following
The cylinders have been honed and checked for tolerances
new rings
new pistons (stock size)
the connecting rods have been fluxed and had a brass insert installed for the wrist pin
extra oil holes have been drilled in the main journals as per Sean's advice.
Crank checked an polished

Any other things I can do to ensure a strong running lower end that will last?

DJ

 

[PATMAX]

Well, a cam change to Megacycle cams is not maching but will change your lift and duration for the better. One can port match the intakes and maybe the exhausts, at least deburr them. ARP head bolts won't hurt either.

 

[4gasem]

Keeping it as close to stock as possible will give you (in most cases) the longest life.

Sounds like you did all the right things. You could polish the exhaust ports on the head, and level the heads, but if you want all out reliability, as close to stock is probably your best bet.

Chris

 

[one2dmax]

You can take off .040" off the block to increase compression. The issues you will run into by shaving the heads (or block) is exhaust fitment. It won't fit for shit the first few times until it bends/warps itself into place.

Your better option would be to buy a 2mm stroker crank from me (if you have stock pistons). The stroker crank lets the piston travel (up and down) farther which makes it bigger CC's as well as increasing compression to 12:1 without buying any pistons! So, more torque from the stroke and more HP from the CC increase and compression.

Sean

 

[satariel666]

But, more rotational mass by increased leverage....which leads us to lower rpms whatever could be obtained.

 

[dij0674]

Przemek, I'm interested in what you're talking about. If I understand you correctly, you are saying that by increasing the rotation of the crankshaft we increase the leverage and there for have to use lower RPMs. Is that correct. Does that mean a stroker can't turn 9000 RPM and will produce more power in a lower range?

 

[satariel666]

Sorry, my english is somethimes hard to overcome LOL

By making the rod longer we are creating the extra leverage beteween piston and crankshaft journal which at last, provides the extra rotational mass.
Then more stroke then more torque - that supouse to be the rule but it isnt.
It is strongly dependale by some critical parameteres but - yes we can say that becouse in most cases we will obtain the higher torque at lower revolutions by making the stroke to be longer.

But, like anywhere else we have a side effects of this modification.

The first one is the fact that total "lower end" balancing efficeincy(LOL im not sure thats a correct term) will go out of spec and it needs te be rebalanced.
More to say after this mod you need higher spec balancing - that becouse we are dealing with higher torque at longer leverage - which "loads" the crankshaft more.

Since the Seans mod contains the reinforced crank and rods I bealive the only thing you should consider is to lower your max rpm.
And also I bealive that peak torque and power will lower its place on rpm curve anyway.

Hope that suits you :ummm:

 

[dij0674]

Thanks Przemek, you explained the concept well.

 

[MaxMidnight]

Moving the crank pin out to lengthen the stroke will increase the leverage that the reciprocating masses of the con-rod and pistons exert on the crank which in turn will alter the balance factor of the crankshaft.
Put very simplistically the balance factor is the percentage of the mass of the reciprocating parts compared to the mass of the crankshaft bob weight(s) and is typically between 50 and 60%.
The crank would need to be re-balanced to bring it back to OE spec.

Another factor to considered would be if additional mass, whether this be to pistons or rods, is added following (say) re boring to increase capacity. It will not only alter the balance factor but also the loading on the rods and crank at top and bottom dead centre.
The pistons of my 1300 only weigh a few grams more than OE, but to keep the same loading the revs need to be reduced by approximately 300 rpm.

As suggested above, it is a good idea to match the inlet stubs with the inlet ports. First job is to mark each stub so you know which port it is matched with.
Once you have removed casting marks and any other lumps and bumps and the ports line up then make sure that you leave a relatively rough finish to the port (i.e. DON'T polish them). This will encourage some turbulence which will discourage the air/ fuel mixture from 'pooling' on the walls of the port.

 

[dij0674]

Thanks Przemek, you explained the concept well.

 

[satariel666]

Thats exactly what I was trying to say but, wrote with an apropriate english.
Thanks.

More to add.
Additional weight will be even multiplicated by the longer rod of course, by some determined relation.

Of course by reinforcing the lower end like forged pistons and h-beam rods, we can slightly raise the rpm limit.
With the "stroking" at the same time we may end where we started even.

 

[KJShover]

Any other things I can do to ensure a strong running lower end that will last?

Three words: Cryo'd Falicon Supercrank unk:
http://www.faliconcranks.com/crank_svc.html

I ran the supercrank in my 250hp nitrous XS and my old 500+hp turbo/nitrous funnybike. Not a lick of problem with the bottom end at all.

Definately well worth the cash.

 

[satariel666]

Three words: Cryo'd Falicon Supercrank unk:
http://www.faliconcranks.com/crank_svc.html

I ran the supercrank in my 250hp nitrous XS and my old 500+hp turbo/nitrous funnybike. Not a lick of problem with the bottom end at all.

Definately well worth the cash.

Sir yes sir :biglaugh:

 

[Rand-5107]

Back in the Day, Piston speed was always a limiting factor.

 

[MeanMax]

I had my heads shaved .020 by PCW this winter. Have put about 150 miles on it since the snow cleared off the roads and it feels better by the seat of the pants but no numbers on paper yet. Parts-Valve seals, head gaskets, cam chain tensioner gaskets, Labor-remove and clean valves, install seals and machine the heads came to $327.43 Great guys to deal with too. Hope it helps!unk:

 

[one2dmax]

Our stroker cranks are done for us by Falicon. The last one we had done weight 1lb less and was rebalanced at the same time. We also ligthened the flywheel (about 1lb) and balanced the assembly to the rods and pistons (as well as rings and pins).

Sean

 

[MaxMidnight]

For any saddo's who's want to work out the inertia loads on the reciprocating parts (Mr M's hand goes up), use the following formula:

At T.D.C.
0.0000142WN[squared]S(1+S/2L)

At B.D.C.
0.0000142WN[squared]S(1-S/2L)

where
W = weight of components in pounds
N = r.p.m.
S = Stroke in inches
L = Length of con rod in inches

It can be seen from the formula that as it is the square of the r.p.m. a small rise here will result in a large increase in inertial load. i.e. Why it is a bad idea to over rev the motor!