[Lasse H]

Is there any reason not to use hypereutectic Chevy 305 pistons with 77.5mm stroke? It just sounds too good combination to be true!
My block is missing 0.75mm from top and 1.9l head 1mm. Because of "too short" compression height of 305 piston it would still remain about 1.5mm below the top of the block, but with flat top pistons my CR would be approximately 10 or near which is quite good for street applications, I assume.

The light weight of 305 pistons and pins (and a 77.5mm crank) really attracts me. And those prices. But I'll have to check availability here next week. At least TRW should have suitable pistons (found from Flatlander Racing catalog).

Btw. the head I would use with this block is a ported 1.9l from 1972 with 42/37mm valves and bronze valve guides. Camshaft Enem X1 (duration 284, lift 11.7mm), hydraulic lifters, aluminum retainers and Crane 1x springs. On monday I'm going to buy Dellorto DHLA 40 sidedraft carbs and then start designing short intake manifolds and air cleaners (or an airbox) for them. It is kind of strange (but quite normal?) how a little tune up project slipped out of hands.

Lasse

 

[RallyBob]

Yes, it will work, but the quench area will be pretty messed up. So the engine will lose some efficiency, as there will be a large gap between the head and pistons at TDC. Remember, the conrods have to be enlarged for the larger Chevy pin too. 305 Chevy pistons are available in cast, hypereutectic, or even forged in some sizes.

One thing though, maybe you should consider using steel (chromoly) or titanium retainers. For a racing engine, aluminum is okay, it's light and cheap. But they need to be replaced every year. I've seen many engine failures from aluminum retainers , since the 'keepers' or valve locks can pull through them with time.
Just a warning if this is for street use.

Bob

 

[Hammer]

Also note, when you are englarging your pin end of your conrod, you can offset the hole to give you a slightly longer connecting rod. And also run nice full floating pins if you put in a nice sleeve in the rod as well
I didn't do this with a GT, rather a V8 thing I did before to bring the pistons up to the proper height.

 

[RallyBob]

Offset-boring the small end of the rod is a lot of work, and you only get .010" gain in rod length. Not enough really. And I don't recommend putting bushings in Opel rods to make them full floating, there's not a whole lot of material there. I've had two rods fail from this, they ripped open at the small end of the rod, and I used the thinnest silicone bronze rod bushings I could find from CV Products. You 'could', alternatively, deck the block a ton to get the piston/deck height corrected, but then the head bolts will likely need to be shortened to prevent bottoming, and the timing chain will need a longer tensioner, as well as cam timing needing to be corrected.

Bob

 

[Hammer]

Ah, thanks for that. I have not taken one of these apart before, and do not know the tolerances. So much for that trick

 

[oldopelguy]

retainers

Has anyone had much luck with teflon wrist pin buttons on an Opel? I swear by them for VW build-ups, but havn't found a set to try on an Opel yet.

 

[RallyBob]

Venolia makes them, but not too many people opt for them. There's no need for them with pressed pins, only floating pins. I use to spec all my pistons with double Spirolox anyway, so I don't know if the teflon buttons are necessary at that point. Couldn't hurt though....

Bob

 

[Lasse H]

Thanks for information and that retainer tip!
But I still want to try how that kind of engine would work. If it simply doesn't, I'll build a normal 2.0l block with normal 95mm pistons.
However, buying hypereutectic 305 pistons doesn't seem to be an easy job. I found one company that told me they could probably sell me +.030" oversize pistons, but with four valve notches. Two too much... They also told me normal cast 305 pistons are something I should stay away from (quality maybe not best possible?) and I really wouldn't like to use forged pistons on my street engine.
One more bad thing is that it is not yet certain is it possible to sell me only 4 or 5 pistons, or do I have to take all 8. That's something I wouldn't like to do, because the price would probably be 40-50 euros per piston.
Does anybody have idea are perfectly flat top hypereutectic 305 available even in the US? And prices there? In Flatlander Racing catalog reads price $129, but for how many piston that is? It doesn't sound like of a price of 8 pistons, but it is quite much for one (I think). But well, still lots of cheaper than some Wiseco CIH forged pistons, about 210 euros each...


Lasse

 

[RallyBob]

Yes, that price would be for a full set of pistons (you gotta love cheap Chevy parts). In fact, when I built my 2.4 litre engine from a 1.9 litre, I used dished-top forged TRW pistons for a 305. They cost me $28 each!

You won't find 305 pistons that are made with 2 valve reliefs unless you have them made custom, the reason they are made with 4 reliefs is so they can be reversed to use on each 'bank' of a V8 Chevy engine. Much cheaper to manufacture, otherwise they have to make 'left side' and right side' pistons with 2 reliefs for a V8 engine, since the piston pins are offset.

Bob

 

[mjustice]

Be careful if you try to do this!!!!
I just inherited a '71 GT from my father that had done the exact same thing you are trying. He used the Chevy connecting rods
to get a longer stroke , be neglected to check for tolerances. After he had done all the work, the pistons were barely hitting the valves, so he took a grinder and took a little off the top of the pistons. (i know VERY bad idea, which i told him at the time, but he was frustrated.). Also, when he did this, he went to what he thought was a reputible machine shop (it wasn't), and when they re-sleeved the block they weren't exactly straight, so of course i have problems with piston slop also. The only way i can see to correct this is buy a new engine! (i'm not the specifics if everything he did, but if you want to know i can find out for you....)
Also, for some reason after this mod, the engine tends to overheat, especially in hot weather. Would a 3 core radiator help?
Anyone know?

Also, does anyone know what this mod will do for the SCCA classification for SoloII??? Would it up my class to FSP (prepared)?
Or would it be higher? I'm thinking of running it, bad engine and all...If it blows, oh well i need a new engine anyway!

 

[RallyBob]

Just FYI, intalling longer connecting rods won't change the stroke....it only changes the rod ratio (rod length/stroke ratio). Of course, installing longer rods requires the pistons to have a shorter compression height (or pin height), or the pistons will protrude above the deck the same amout the rod length was increased!

As far as the overheating, it is probably due to the block having been bored out excessively. If, for example, 283 Chevy pistons were installed, the bore would be so much larger (.215") that the cylinder walls get VERY thin, and build heat quickly. They would also protrude above deck by about .030". A thicker radiator would help, but would not solve the problem.

For autocrossing, the internals of the engine must remain stock for Stock class, and also for Street Prepared class. For Prepared class, you can overbore as much as .047" and change the compression ratio, and that's it. You can't change the stroke. So, your engine would put you into Modified class, which is the domain of some VERY fast cars with slicks and very light weight. The Opel won't be competitive there unfortunately, without a very large cash infusion.
For autocrossing, I'd concentrate on two things: The handling of the car (esp. tires and alignment), and the driver. That will ultimately decide the car's competitiveness.

Travis, if you read this you can comment on the rules better than I can, it's been a few years since I've read them fully, and I know you're deep into an EP GT project right now.

Bob
"Former driver of an E-Prepared Ascona, only beaten once in 1993"

 

[mjustice]

I knew the the 305 pistons didn't sound quite right!
And, that also explains why he had to have to block bored and
re-sleeved...
Thank you for your insightful explaination if why it's been overheating, it explains why nothing i have done has helped my problem. So, it looks like i'm stuck with it until i can afford a new engine (which might be a while...single income, married, 3 kids)
I'm just happy that I was able to squeeze enough cash out of my wife to get a paint job so it won't rust! It's been sitting for about 4 years now, paint's faded, etc....I will try to post some before and after pics after i get it painted. I explained earlier that i inherited it from my father, and i want to clarify that he hasn't passed, just that had too many vehicles already. The reason he parked the Opel was that he said that he had to work on it too much. So what does he do? He buys a Harley and gives my the GT! Go figure!

Honestly, i don't care which class i'll be running in, since it's going to be my rookie year, and i know i'm going to lose anyway, But i don't want to look like an idiot and register for the wrong class my first time out.

 

[RallyBob]

I think you got the last laugh....if he thinks Harleys require less maintenance, he's in for a surprise!

All kidding aside, I'd see if you can just find a 'junkyard' shortblock and throw that into the car....at least you'd be legal for a lower class and you could get it together for very little investment. Too bad you're across the country, I have dozens of used shortblocks that could get away with being used 'as is', or could be re-ringed (re-rung?) and have new bearings installed for cheap. Throw in a gasket set and you're on the road again.
Any west coast Opel people willing to donate a shortblock to mjustice?

Bob

 

[Travis]

Not much has changed Bob. .0472" overbore, pistons are open except they must be metal. rods are open but they must be ferrous. no change in stroke though you could probably get away with stroking to the max tolerance if specified in the shop manual. I've heard of high end circle track people doing this for the extra fraction of a percent. Way too much effort for no return...interesting though.

-Travis

 

[ftl]

Timing Chain Tension for Milled Block

I'm trying to build a 1.9 with 305 pistons and a stroked crank (0.125" at crank for 0.250" stoke increase). I just talked to the machine shop who thinks we need to cut about 0.105" from the block to get the squish area right (about the head gasket thickness) and the compression at about 9.5:1.

I understand that we will have to be sure the head bolts do not bottom out after reading a bunch of posts on this. We will also have to modify the upeer cam gear to get the cam timing correct.

The concern from the machine shop is the cam chain tensioner. With a new chain (of course), can the tensioner make up for that much slack?

If not what alternatives are there? I've seen mention of extending the tensioner piston. How would that be done, and how much woudl be required?

Thanks for any help.

 

[oldopelguy]

Why?

If you're going to stroke the crank anyway, why not go another .105 and leave the block height alone? Seems to me it would be a ton easier.

Alternatly, leave the stock stroke and use a slightly longer con-rod. Dimmensionally the 2.3 ford ones are pretty close.

I've wanted to try a VW air cooled piston/rod combo for a while as well, as there are thousands of variants out there for that motor and they are all relativly cheap.

My $.02 worth.

 

[ftl]

Why??

Well the crank has already been stroked. I agree adding some more stroke would be the easyest and is probably the best solution. When the machine shop decided to go for 0.125 stroke I had understood that they had already figured out the piston deck height, but methinks a mistake has been made. It may end up with then re-doing the stroking.

 

[calvin]

redoing the distrib is tricky too. I am not quite happy with it right now but will continue to play till I find the optinmal setting.

I think the power gain is worth all the effort.