BritishV8 Forum

There is an argument against fitting larger valves when it involves larger seats, but that has to do with increasing the potential for cracking between the seats. As for larger valves sometimes costing power, that could happen possibly, but only if the system is optimized for the smaller valves.

JB

Also depends on the chamber design as with a rover/buick chamber shape the valve head can become shrouded and you can end up with reduced flow until you get to approaching max cam lift, resulting in an engine with poor torque at low RPM.

You will often get better results from using a smaller inlet valve with carefully optimised area just below the valve head and correctly sized runners.

If you look at the chamber design of the merlin heads you can see how the low lift flow has been enhanced by the chamber shape which has been proven by the dyno testing where they produce a strong almost flat torque curve from above 2000 RPM.

Kevin.

After doing a little research on the web I found some oversized valves that may work without replacing the valve seats. VW 2.0 type IV valves are 4.606" over all length,  in 1.65" head, ex 1.41" head, and 5/16" stem. The exhaust may be a bit large and if so I could go with the 1.4" size listed on multiple performance rover sites in the UK, or, if possible, turn the valve down. The only problem I see mixing the in and exh valves  brands is keeping the springs, retainers and locks consistent across all the valves. Does this seem feasible and a more economical route than going the full tilt jumbo valves and seats?

Justin,

Are the VW valves the same stem size as the rover ones and are they waisted stems as per the rover big valves?

The difference in area for the inlet is relatively small, just wondering if it's really worth all the hassle.

Kevin.

I'm not sure if they're waisted but the intake is 1.65" instead of the stock 300 1.63" and it turns out that I can get a 1.4" exh valve. Seeing that I have to replace the valves regardless I might as well go with the biggest valve I can get without replacing the seats. If they're not waisted might be the deciding factor, although how much smaller is the waist than the stem and what is the stock rover/buick stem? The VW stems are 5/16" and the Buick v6 stems are, I believe, 11/32" and the stock 300 valves may be up to  3/8"... so how much would be lost going to a non waisted stem that's  between 1/32-1/16" smaller in diameter than the stock stem before the waist?
There is also a 1.73" option but that would probably mean new seats.

Just sizing up a 3.9 build for the dragster, hows this for a stock parts line up. Stock 2.8 stroke, 6" SBC rod and a stock dimension 305 piston, gives 8.96 deck less 1.4 or stroke less 6" for rod and 1.54 compression height for a piston .020" in the hole, some manufacturers use 1.56 compression height for a zero deck. For a stroker option we would need 3.4 stroke to use a stock 5.7 chevy rod. More food for thought.

Alan

Another valve question...Where would the biggest gains in flow come , a .020" larger valve head (1.65" vs 1.63") and no waist on the stem, or stock head and a waisted stem?

Justin, good question for a flow bench savy person like Dan Jones. My experience,(limited) ,leans towards the "shape/angle" of the valve more than +.020". Concentrating on low-mid lift enhancement, will show more rewards, for a street based motor. Stroking a 215/Rover by 1.05" will produce a bad L/R ratio and high side loads on cylinder walls. Alan,"for the dragster", how would we offer suggestions to this ? Good Luck, roverman.

Art, by "shape/angle" you're saying that I'd be better off by using a waisted stem?
As far as stroking the engine the combo I've come up with is using Icon IC835 chevy 305 piston (thanks for the suggestion) with a pin height of 1.133", 6.125" chevy rods, and  a 4.6 crank offset ground to 3.404". That gives zero deck clearance, rod ratio of 1.8:1 and a displacement of 299cid.

Justin, The 5/16 stem VW valve is probably close to 11/32(waisted) dia. Is it long enough ? I know of no flow spec's for your valve, in a 300 head. Nearly all int. valves benefit from a 30 deg. back cut. Exh.-no, but want a carefully blended radius on chamber facing edge,(helps air flow over edge)FWIW, sounds like your heads, as described, will flow around170cfm. on intake side. Should equate to a warmed-up street motor. Are you installing flanged liners ? Otherwise, 3.736 bore in std. liner, might be "iffy". Good Luck, roverman.

The over all length of the type IV vw valves is 4.606" and looking on a couple of UK site the rover valves  are between 4.595 and 4.612".
I'm not installing liners...that just puts the overall cost out of the fun to $ ratio. When you say iffy what does that mean, that is what are the possible consequences of trying to to go .040" over? The other possibility is to use the Ford 4.6 pistons with a pin height of 1.22"(3.7" bore), 6" chevy rods, 4.6 crank ground to 3.48", but the rod ratio is not as good @ 1.72:1

Justin, To put this in proper prospective, 400" sbc's have a rod ratio of approx 1.45/1. I would use 1.72/1, if the combo worked-out. Good Luck, roverman.

Art, That combo is probably the best best and least risk, I just like the chevy 305 option better...better rod ratio, don't have to rebush the small end of the rod, but the pistons are just too big :-/
More valve questions... I found this info on valves, apparently Datsun/Nissan 510/240z valves are the right length, stem diameter, and have a 1.715" intake head diameter which I'm hoping will work in a 300 head without replacing the seat. Any Idea on where to find Datsun 510/240z valves? I've searched and can't find any info or even price on them...any ideas, websites, suggestions? Here's the link http://www.v8buick.com/showthread.php?t=121528&page=2 post #32

May be it can help you for valve option. In Uk a compagny called REC produces racing valves for RV8 :

REC 315 V8 3500cc 1.630"/41.4mm Inlet Std. Stem, Std. Groove
REC 460 V8 3500cc 1.692"/43.0mm Inlet Std. Stem, Std. Groove
REC 477 V8 3500cc 1.692"/43.0mm Inlet 5/16" Stem, Triple Groove
REC 477/1 V8 3500cc 1.692"/43.0mm Inlet 5/16" Stem, Special Groove
REC 508 V8 3500cc 1.750"/44.4mm Inlet 5/16" stem, Ford Pinto Groove
REC 456 V8 3500cc 1.844"/46.8mm Inlet 5/16" stem, Ford Pinto Groove
REC 117 V8 1.350"/34.3mm Exhaust
REC 316 V8 3500cc 1.400"/35.5mm Exhaust Std. Stem, Std. Groove
REC 461 V8 3500cc 1.455"/37.0mm Exhaust Std. Stem, Std. Groove
REC 478 V8 3500cc 1.455"/37.0mm Exhaust 5/16" Stem, Triple Groove
REC 478/1 V8 3500cc 1.455"/37.0mm Exhaust 5/16" Stem, Special Groove
REC 509 V8 3500cc 1.470"/37.3mm Exhaust 5/16" Stem, Ford Pinto Groove
REC 457 V8 3500cc 1.556"/39.5mm Exhaust 5/16" Stem, Ford Pinto Groove

The major advantage of REC valves, they are available with 5/16" and are very light.

I have 477 and 478 in my Tuscan Race Heads.

What modifications did you need to do to make these valves work? That is did you need to shim rocker stands, use different length springs, or any other mods that stray from the stock specs?

Just thought I would add my $.02 here from my build.

4.0l rover ($125)
Crank offset ground to 1.89 journals ($300)
Nissan VG30 rods, 6.070 length, and the kicker, they are the perfect width.($200 for 12 stock used rods, + $ for reconditioning and arp bolts, or $700 for aftermarket h-beams)
Custom Ross forged pistons ($450)

Rover 4.0L heads ported to a minimum CSA of 1.5"
Isuzu 2.8v6 (Chevy 2. valves, 1.718 intake, 1.424 exhaust, 11/32 stem, 4.707 length ($80)

Haven't worked out cam and spring solutions, but I am going with bigger seats @ 88% of the valve diameter.

I'm sure you'll be most interested in my valve and rod choices, but feel free to comment on any of it, or question what I left out.

"Custom Ross forged pistons ($450) "
What are the specs on these and are they really custom for $450? I emailed diamond and they gave me an estimate of over $1k

Don't have the specs on them yet, still need to true up the block and heads, so depending on how much is decked off those we can decide on the final compression height.  The crown is going to keep the stock dish, more or less, to keep compression down to about 10.5-11:1, and compression height should be in the 1.1-1.15 range depending on final deck height.  Not going to be much good for nitrous or forced induction.  It will keep weight low and make balancing the crank cheap, mallory can get expensive.

$450 may be low, but my machinist is a Ross dealer and he is probably just cutting me a deal.  He originally told me $450-$600 before I had him doing the valve job on the heads, machining the block, and offset grinding the crank.

Need to make a few additions and edits.

The Nissan rod journal is 1.967" (50mm), not 1.89" like Honda.  The big end width is .8170", just for reference.  I also found eagle H-beam rods for $460 for 6, then $80 each for the remaining 2.

Unfortunately when my machinist got a quote on the pistons, all the guy heard was Miata, and quoted on a set of 4.  The complete set I just ordered set me back $725.  Still not too bad, but I will be going with the stock VG30 rods now, can't spend another $620 for Eagle rods.

Also, I couldn't find a good deal on a 4.6l crank, so I will be offset grinding the 4.0l crank I already have to roughly a 3" stroke.  This obviously frees up another .3-.4" of compression height to build a stout piston.  Maybe it will be able to see some juice one day.