rebuilding engine - some questions

[kikkegek]

I am rebuilding a new engine and I am also interested in this ideal quench discussion I found in the thread about highest CR run on propane engines. Also any other advise is welcome.

its a 1970 chevy small block (010-020 high nickel casting) 350ci
stock crank, 3.48 stroke
has not been overbored before. But will now probably be bored at .04 because of cilinder wear (worst cilinder dimension is 4.0305)

will be adding a new camshaft. Comp cams told me XE250H, but I am also looking at SUM-K1101 or K1102

I want to use 64cc heads to up the CR a little (it had 76cc heads), use a thin head gasket (compressed .035"???) but I am not sure what pistons to select?

I see pistons are available in several "heights" and "different "head volumes" and two or four valve relieve...etc...probably will go for hypereutectic flat tops...but then there is stilla lot of different versions available.

and what is the ideal quench for propane and gasoline?

any advise on this engine build will be welcome.

I want to build it for propane, but if needed be able to convert/use it for gasoline (depends on legislation from our government)

[kikkegek]

while surfing the net I found some nic einfo on the quench-squish part of my question.

1. I found, but cant find it anymore, that Franzh stated somewhere that propane engines with a compression ratio over 11 or 12 should be treated as if they were gasoline fired engines when doing calculations.

2. found this nice article on the net
http://www.chevyhiperformance.com/tech/ ... nce_guide/

near the end it says:

According to Ken Duttweiler, the tightest quench he recommends is around 0.050-inch.

and

We tried this on a recent dyno flog of a 383ci small-block. To keep the compression at around 9.5:1, we used a set of 0.050-inch head gaskets that created a wide piston-to-head clearance of around 0.060 inch. CHP engine flogger Ed Taylor swapped in a set of 0.040-inch Fel-Pro head gaskets and then tested the engine again. We witnessed only a marginal gain of around 2 to 3 hp (less than 1 percent), but it’s doubtful that the marginal increase in compression was responsible. Clearly, tightening quench with a thinner gasket had something to do with the increase in power. Tightening the quench area often results in the reduction of ignition timing requirements. This can then lead to a reduction in negative work (the cylinder pressure rising while the piston is still approaching TDC). This often is evidenced by a gain in low- and mid-range torque.

and

most production engines rely on a piston-to-head clearance of 0.060-inch or more in this area.

So I guess there wont be a very big performance gain in my engine if I go for a .035 or .05 head gasket.

also most benefits I read from a tight squish/quench is directed to gasoline use, such as better mixtures of gasoline with air, preventing lean spots and detonation. While propane is already gaseous and much less sensitive to detonation as gasoline.

since I am focusing on propane I am propably just fine using the 64cc heads and a regular gasket.

Right?

So now I wanna focus on selecting pistons...and there is just too much choice...I definitaely dont wanna go into the expensive performance stuff, since I run my eigine only between the 1500-2500 range and mostly around 2000rpm...even if I step on it, it will shift well before 3000rpm...only with WOT it will shift at 4000rpm...but that is only in a rare occasion...

any advise on pistons?

[Frank]

I am far from an expert with respect to rebuilding engines but my understanding is that quench is used to induce turbulence in the combustion chamber. The greater the turbulence, the faster the flame propagation. The net effect is a reduced need for ignition advance.

Therefore, the ideal quench would be the minimum amount that prevents any collision between the piston and the cylinder head. For a given compression ratio, flat-top pistons work better than domed pistons. If you need to retain the possibility of running on gasoline, select a compression ratio that is compatible with your highest octane gasoline. In an earlier topic about CR, Franz recommended the following:

A good solid street engine with moderate camshaft timing, which would need good idle and mid range can use around 10.5 to 11:1

[Steptoe]

So I guess there wont be a very big performance gain in my engine if I go for a .035 or .05 head gasket.

had this argument for years.....I agree and its not worth the added risk of the thinner gaskets blowing, espec on street engine....track yes as these are normally stripped after every few meets anyway

I run 327 64cc cast iron 202 fuelies... which have been skimmed a few thou 3 times from new
They have also been cc ed with and casting dags removed....the higher compression makes things a little more p-rone to detonation, doing so never had such an issue since doing so.

I run ACL flat top pistons giving a cyclinder pressure around 220lbs from memory... bores machined and final honed to each matching piston of 1.5 or 2 thou clearance... from memory....u may find many piston manufactures for LPG recommend an extra thou ...as per a race engine spec... personally believe ...after spending some time in the local ACL labs... this is a do not sue us out thing... where ppl over advance initial lean mixtures on initial fire up doing damage.

And yes there is the question should u fire up on petrol or LPG... well its my understanding that GM did and maybe still does intial fire up on lpg for petrol engines.

[BigBlockMopar]

If I had a spare engine to play with, I would shoot for 0.035" compression height by using a thinner headgasket.
If all fails and the engine pings (in your heavy car), you can always lower the compression ratio by replacing the headgaskets with regular thick or thicker ones.

[kikkegek]

If I had a spare engine to play with, I would shoot for 0.035" compression height by using a thinner headgasket.
If all fails and the engine pings (in your heavy car), you can always lower the compression ratio by replacing the headgaskets with regular thick or thicker ones.

the cilinders will be overbored to 4.030

do you really need to buy a matching 4.030 gasket ? because there are only 2 available from Summitracing.com

[gottago]

I see pistons are available in several "heights" and "different "head volumes" and two or four valve relieve...etc...probably will go for hypereutectic flat tops...but then there is stilla lot of different versions available.

Any decent quality flat top hypers in about a 10:5 would seem as good choice as any but remember the aftermarket manufacturers usually rate them at a zero deck height. Stock chevy pistons are usually down about 20thou from there. To get the quench down to .045 or less is a bit of a hassle. Having the block decked a bit to clean it up could help out but go too far and you have to plane the intake to match. Best off the shelf head gasket I could find was an .038, the thinner ones than that either get real pricey or you are taking big chances on sealing. Deck the block to about 10 thou and you would get in the ball park for the upper end of quench with the 038 gasket. Shouldn't have to plane the intake if decking is kept conservative but I'm not sure the exact cutoff point. But zero decking would get you a decent quench with just the .038 gasket. choices choices lol

You would probably be best with a real low rpm intake manifold and as small a cam as they come in one of the the new torque grinds.

[kikkegek]

thanks guys,

also have a question on camshaft selection.

I have given all my specs to Comp Cams (except for the 64cc heads, because they were 76cc heads in the query) and they told me to use the XE250H cam.

I have looked into Summit and found the K1101 and K1102 pretty simular. the K1102 seems allmost identical, but Comp quotes this cam for 600-4600 and Summit quotes it for 1500-4800 rpm...

I am no cam expert, did quite some readin, but cant reeally decide. Can you guys spread a light on this question?

[gottago]

Of those choices, I'd lean to the smaller duration comp cam on the tighter 110 lsa. The other two have way more duration than you actually need for your intended purpose. I might even consider a shorter duration yet like the little 108 lsa version. Concentrates the power where you drive.
http://www.compcams.com/Company/CC/cam- ... id=70&sb=2

Or like the big brother -high energy marine cam
http://www.compcams.com/Company/CC/cam- ... id=71&sb=2

[storm]

The advertised duration is very different, that is why the Comp Cams cam has a much lower rev range than that Summit cam. For torque, which I assume is what you would prefer, I'd be going for the Comp Cam.

[Steptoe]

I go with gottago choices above espec the
http://www.compcams.com/Company/CC/cam- ... id=70&sb=2
For a street cruiser application ...thu with LPG I prefer a little more lift closer to the .5

[gottago]

The cam above is a nice little runner but everything else has to be just right in combination to make it work. It is bare minimum for an application as yours kicka but as said, adding more lift would give you the added torque to compensate for gearing/ weight / etc. The short duration and the tight lsa (108) would work well but the low lift athough would give excellent fuel mileage would likely leave you wanting more on big hills etc. The difference between this much lift on this short of cam and up at .500 lift is night and day. One is fuel mileage daily driver with decent low end power and the other would near shred your tires. Somewhere in between would give you a nice compromise.

The little cam also has very little overlap, maybe even less than the comp cam XE250H above. It would be quite reponsive and there are others like it with a bit more lift. That comp cam is still a decent choice though imo. You don't want to deviate far from those numbers for a daily. I went with a small extreme 4x4 cam in a little 305 chevy a while back but mainly due to the intake I was using. Mileage is very good, torque is much improved, yet it still has more at the upper end of the rpm band that I don't need or use in this application. Its just an around towner parts runner. I may have been even better off with the little cam in hindsight, not that there is anything wrong with the other, just more than I needed. Its tough to make the perfect choice right off but I recall you have been looking for some time and are definitely in the ball park imo.

[BigBlockMopar]

I am no cam expert,

Is Summit a cam-expert?
How about CompCams?



What information exactly did you give CompCams?
With your higher then mentioned CR you might end up with too much cylinder pressure and end up with a 'pinger'.

I'm currently dealing with something similar with the 500" stroker in my '60 NewYorker.
I' ve installed an Extreme energy rollercam, but with the longram intakes and 10.5 static engine CR, the motor pings when getting on the throttle.
Part of that is caused by the underhood temperature, which heats up both carbs hanging over the exhaust manifolds, so I'm desperatly looking to build a cold-air intake solution now.

[gottago]

Usually 10.5 static isn't a problem with pinging on lpg. Intake design is an often neglected aspect to consider. Head design very important, quench necessary if large inefficient combustion chamber. You mention carbs hanging over exhausts bbm, you do mean mixers and are on propane? I have a 460 in a heavy tow rig that was pinging like that even under light load on hills. It would go away with more throttle and I eventually replaced the vacuum pot on the dizzy with an adjustable one. Recurved it and all good now.

The chevy 64 cc head depending which one I suppose, had a good fast burn design and seemed to take well to compression under 11:1 without needing much cam to keep the dcr down at lower levels. The comp cam choice mentioned by kicka above appears to be in the acceptable range.

You have the smaller comp extreme energy roller cam or one of the larger ones bbm? How much overlap? How much static compression? Dcr? What heads are you running?

[BigBlockMopar]

I've got a XR274R. It's an CompCams Extreme Energy rollercam. Engine has 10.5:1 static cr with alum. Edelbrock heads.
Here are some pics and info about the engine and car; http://www.bigblockmopar.nl/cars/1960-c ... newyorker/

But the stroker engine of mine is running on gasoline so I won't go into it much further here as to not hijack or dilute the topic with irrelevant info.