Opel GT Forum banner
21 - 40 of 61 Posts

·
Super Moderator
Joined
·
13,943 Posts
Large valves alone usually don't affect drive-ability. In fact every head I've done with large valves, regardless of make, has improved drive-ability/torque. The porting work that accompanies the larger valves is usually to blame when drive-ability suffers. Keep the ports moderate in size, or increase compression at the same time to improve vacuum/draw into the system, and you will lose nothing. Modest increase in other areas (exhaust diameter, intake manifold porting), will typically enhance overall drive-ability.

But changing one area of the engine only, and making too radical a change, will almost always make the engine *unhappy* is some respect. Many people do this, then blame the modification. Too big a cam in a stock engine, too big an exhaust on a stock engine, too much compression. Engines like to be modified with symmetry in mind. Make smaller changes to multiple areas to retain balance, and the engine will respond accordingly.
 

·
Super Moderator
Joined
·
13,943 Posts
Okay, as promised, here's another view of the big-valve head I was working on. Here, the ports are untouched but the chamber has been unshrouded (1.9 bore).

Bob
 

Attachments

·
Super Moderator
Joined
·
13,943 Posts
.......and in this photo, you can see the ports themselves have been enlarged substantially. BTW, I photographed the same chamber step-by-step to show the differences. Although this head has not yet been flow tested, typically a stock Opel head will improve from 88 cfm to about 125 cfm with the changes I've made here. In fact it will easily outflow a stock 2.0, 2.2, or 2.4 head.

Bob
 

Attachments

G

·
1 (or 2) more questions

Before I take my head down to the machine shop to have new valves put in, I have a couple of quick questions for Bob from an application standpoint:
With Chevy valves, can I get away with Chevy valve stem seals? I have a couple of sets of Opel ones, but Chevy ones are sooo much cheaper!
Do I need to unshroud the chamber before I get the valve job done, or is it easier to do with the valve in it's seat (being careful not to touch the seat of course?) It seems it would be easier to cc the chambers if the valves were in and sealing, but I may be in left field on that. Do you even cc them, or just go by eye and feel?

On a different note, did the 2.4 litre with 305 pistons and a supercharger ever pan out? I've got a couple of extra blocks I'm itching to take to the machine shop for flat top 305 pistons on a stock crank for a blower/ turbo low compression motor.
Stephen
 

·
Super Moderator
Joined
·
13,943 Posts
You can't use Opel valve seals! The Opel valves are 9 mm, Chevy valves are 11/32. You need new guides, new valves, new seals, you SHOULD install exhaust seats, and you'll need new springs, retainers, and valve locks. Otherwise it won't work out.

If you are installing larger valves, you have to cut the seats before you can unshroud the chamber. I use old dummy valves installed in the head to prevent seat or valve damage while grinding. Cc'ing is overrated. Not necessary on a street engine. Other than for calculating true compression ratio, it serves no purpose for 95% of the enthusiasts out there.

I never built the blower engine. Too many distractions! I built the 2.4 shortblock, ran it in naturally aspirated form for a while, then tore it down to inspect for wear ( I always do this when building new concept engines). I had the block re-honed, and wrapped it in plastic,where it sits to this day. Some day I'll built the blower intake and put it together. I'm thinking it would go great in my Kadett wagon. Imagine 250+ hp in a 2000 lb grandma car?

I think you'd better invest in longer connecting rods with that 305 Chevy pistoned engine you're thinking about. The piston will be about .210" below deck! Probably about 5.5:1 compression or so! Maybe try a 5.2" Ford 2.3 Pinto rod. Narrow the rod by .0065" per side (.013" total) to fit the Opel crank, and now the piston will be only about .050" below deck.

Bob
 
G

·
On larger valves and torque. Going to just larger valves with proper unshrouding and no other changes, what happens to torque at the low and mid range rpm? I found older message in the yahoo groups saying the larger valves help torque because of larger surface area. I don't understand exactly what that means. I thought the larger valves, without any other mods, like increased compression ratio or cam changes, would decrease velocity in general. Or is it that the Opel 1.9 just needs the bigger valves to help achieve better balance, by making up for the poor intake?

Thanks,
Alan
 
G

·
more on valve springs

You said to use a Pontiac 400 spring about 1.44" diameter. I'm looking at a ordering some good springs and was wondering what the range of size and IH is. I've found a lot of 1.46" springs that i figure will probably have no problem working, but what installed height do you recommend? I don't want to order something too tall that will not work well or just plain be too tall to fit.

And just to verify I want to use a standard length sbc 1.72/1.50 valve, chevy retainers and locks, 11/32" guides and of course hard seat inserts... then after the machining is when I'll want to unshroud and port/polish.

Have you used screw-in studs like on a sbc? I'm pondering this one since my head will be in the machine shop soon. I'll have to take a look again, but I think I could get away with 3/8" studs, use the opel fulcrums and a chevy nut to keep everything together. I don't remember if the fulcrum is like a chevy where it is separate from the nut, or if it is large enough to fit over the stud without being drilled out.

Thanks

Dan
 

·
Super Moderator
Joined
·
13,943 Posts
Okay, this gets confusing. I don't give out particular part numbers because the parts I use these days tend to be a bit pricier than some people are willing to pay. I don't believe in scraping the bottom of the barrel, even for Chevy parts. Here's a general guideline however.

But to try to answer your questions, I use standard length small block Chevy valves. Retainers are critical to establish spring height. A flat retainer will require a shorter spring than a high-step retainer. I tend to go for a +.080" or +.100" height retainer. When the spring seats are machined for the larger spring diameter, the exhaust spring seat is usually the correct height as it is, but the intake must be milled about .055" (don't take this as gospel, the machinist must establish this...there are variances from year to year and it also depends on valve seat depth). At this point, the spring installed height should be about 1.625" - 1.675".

Depending on camshaft choice, spring pressure should be around 100 - 115 lbs on the seat. Do not exceed 125 lbs, stock rockers will break like china at this point! Open pressure will vary as well with spring choice and valve lift, but stay below 250 for a street engine. I used to run 240 lbs with a .430" lift, 242 @ .050" duration camshaft, and valve float occurred at 8400 with this combo. Should be more than adequate for the street.

Opels have screw-in studs already. You can't use Chevy studs for two reasons. One, the flange from the Chevy stud may interfere with the Opel rocker arm. Two, the Opel stud is drilled for oil flow to feed the rocker arm. If you use a Chevy stud, you stop the flow of oil to the rockers. The rocker will burn up in about 3 to 5 miles. I've had the oil galleys plug up before, it will destroy the entire head. Not pretty.

Bob
 
G

·
Thanks for the info. out of curiosity, what springs do you use? I'm not looking to buy the cheapest stuff out there, I'd rather have quality and spend 50% more for the piece of mind. I'm really looking at the 10 degree titanium comp cams retainers. And since everything wants to come in a set of 16 I'll have a full set for my spare head or extras for my current just in case.

Another thing I've found is its hard to find a stainless steel valve smaller than 1.94 for the intake side. Any source for a 1.72 valve in stainless?
 

·
Super Moderator
Joined
·
13,943 Posts
generally use Crower 1.25" springs (see, I'm already going against what I told you), and their 1.25" 7 degree titanium retainers. 10 degree are unnecessary for the street, we've run them to almost 10k rpms with no problems. You can buy these is sets of 8 by the way. These springs/retainers are lighter than 1.45" springs, so they reduce the unsprung weight a little. Also are very reasonably priced.

You can either do what I used to do, which is buy the 1.94" valves and turn them down to the required size, or order them from Manley. They will make them any size, turn-around is very fast. I prefer the undercut stem (Pro-flow?), they flow better and are a little lighter.


Bob
 
G

·
Does it compromise the valve at all turning it down? I guess you could potentially go with any size valve you wanted if that is the case, turn them down to say a 1.78 to get a happy medium between the 1.72 and 1.84.
 

·
Super Moderator
Joined
·
13,943 Posts
I've never had a problem with turning them down. And yes, I've experimented with different valve sizes over the years. 1.72, 1.78, 1.80, 1.84, 1.85, 1.88, 1.92, 1.94 and even 1.97 for the intake side. Exhaust side I've done 1.45, 1.50, 1.55, 1.60, 1.625. Depends on cyl. head type, application, engine displacement, bore diameter, etc.


Bob
 

·
Super Moderator
Joined
·
13,943 Posts
Dan, go to http://www.sivalves.com/ for more info about off-the-shelf stainless valves in odd sizes. They have 1.72, 1.84, 1.88 (for 4.3 Chevy), and even the newer 'Vette sizes with 1.97/ 1.55; with small valve stems. I almost forgot about them, I used to buy a lot from them years ago.

Bob
 

·
Detroit,where my home was
Joined
·
2,991 Posts
RallyBob said:
Hmmm, maybe once I've got the digital camera thing figured out, there's a possibility of creating a "library" of sorts to identify the various heads. Unfortunately, most of the ones I have are already modified, so this defeats the intent of identifying cyl head types easily. But with all the various Opel owners out there, we could perhaps photograph and label the vast selection of heads. 1.5, 1.6, 1.6s, 1.7, 1.9, 1.9h, 2.0, 2.0E, 2.2, 2.4, 2.0 group 1, 2.0 group 2, etc.
don't forget the 1.9 S
 

·
boomerang opeler
Joined
·
5,638 Posts
jeff the 19S is a high comp (9.0/1) from the european market 102 bhp/5400 rpm(gm-test 20)115ft lbs /2800 rpm (gm test 20)
 

·
Registered
Joined
·
2,733 Posts
One of my blocks' serial # starts with *19S, other two start with 19S.
All have different configurations of cast in (raised) logos, one has big square lugs where the motor mounts bolt up. One has a big H just aft of the serial # pad, another has an EB logo there. Two are thick web mains. All came with dished pistons, two had forged rods. One came with a 12 bolt four bearing head, one with a ten bolt four bearing head, one with a ten bolt three bearing head. It's hard telling what their life histories are, all seemed to be quite sad when they got here... The one that came in the Kadett was even tragic. Only thing usable there was the block which was not stock bore size.
I'll have the shop heated up and working tomorrow, will get pics of the two blocks that are candidates for the new race car engine.
 

·
Registered
Joined
·
2,733 Posts
So the 1.9S is 9 to 1 cr, then what difference is it from a regular 1.9, isn't it 9 to 1 cr also?
In perusing my "new" 1.9H head, (thanks Jim, USA Opels!) I can't really see anything outstanding different about it. Except that maybe the combustion chamber is closer to the deck, know what I mean? It looks like the head has been milled a bunch, the dimples are shallower and the Intake seat is right next to the edge between the chamber and deck. But in measuring the height of the head, from the deck to the valve cover rail, it is actually .015" bigger than a 12 bolt head I have to compare.
I'll try to remember to take my camera to work tomorrow and get some shots up here.
I never did find the spec as to what the chamber's volume should be, I thought I saw it here once but can't find it again. Didn't Bob have them all measured out for us somewhere?
Geez I hope I can make 11 to 1 cr somehow. I just love the smell of 110 octane racing fuel exhaust first thing in the morning...
 
21 - 40 of 61 Posts
Top