I was inquiring at my local speed shop about a stroker engine. I was made aware of soemthing I had never knowm, that the longer the stroke, the more of the piston skirt is exposed at BDC, which in turn makes the engine an oil user. I was told that on a SBC the largest to go would be a 408, otherwise it would be into oil burning territory. This sort of burst my bubble, as I had been thinking of going to a 415.

Well, this got me thinking. I also plan on supercharging (ATI Procharger on order) and started to wonder what is the best way to go. When is a stroker too large? Especially when supercharged. Is a stroker even necessary on a blown engine? Well sure, "no replacement for displacement", right?

But if it were up to you guys, the ones who really know about engines, what would you do? Would you go large bore, standard stroke (377)? Or go standard bore, long stroke (383)? Or just go all out, large bore long stroke (415)? And use a little more oil?

When planning an engine that will be blown, is the advantage of a stroker engine redundant with a blower? Or is it "the more the merrier"?

Thanks for indulging my ignorance!

 

With boost, you really dont need all the cubes in my opinion.

All you need is a nice big bore and a GOOD set of heads coupled with 10-12lbs of boost and you'll be flyn'

10-12lbs isn't a lot honestly and it will make a lot of power whether you are turbo or supercharger....just size the turbo/blower to the motor and horsepower goals

All that a bigger inch motor will do is give you much more torque that you will have problems hooking....my thinking is use smaller inches and more boost so that its easier to get out of the hole and the boost picks it up on the top end

 

A stroker also can be an oil user when the piston wrist pin actually comes into the piston oil ring. Also the rod ratio becomes a problem. You might have heard of the ford 302 being stroked up to 360CID, but its rare. The 347 has these problems thats why the most common stroker is a 331. SB chevy is a better block and has better strength and capability.

 

If you're gonna boost it I say go for the standard stroke large bore(377) setup w/ all forged components to take advantage of the high RPM benefits of boost.

 

If you are replacing the rotating assembly anyway there is no reason not to do a stroker, especially for a blown application. A general problem with a long stroke motor is that it can't be revved as high as a short stroker. Since a blower car is much less dependent on rpm to make power, this is not much of a drawback. Another consideration is that valve size is ultimately limited by bore size. So while a stroker increases displacement, the power increase in less than 1/1 proportional to the displacement increase since the valves aren't any bigger. This again hampers an NA motor more than a blower car sice a blower is by definition "forced induction".

But that's based on comparing motors of the same displacement. Within (broad) limits, the extra displacement of a stroker will outweigh any issues related to bore/stroke ratio if the comparison is with a smaller motor. That said, there are some mechanical limits. What you run into first on an LT1 is problems with rod/cam interference and with entering the water jacket when clearancing the block. This makes the largest practical stroker a 396, though it's possible to go larger. As far as bore size goes, the general rule on an LT1 block is max 0.030" overbore for a blown application. Much more than that and the cylinder walls get too thin to seal well - they distort under high cylinder pressure. My current setup is 0.040" over and the next time I rebuild I am using another block as 0.040" over is pushing it. There are combos up to 0.060" over but this require finding just the right block and sonic checking all of the bores if it's gonna work right. I wouldn't go 0.060" over on a blower car with a stock block. And even 0.060" over with a 3.48" stroker is only 360ci anyway. I'd rather have a 383 or a 396 stroker over that combo either NA or forced induction.

Rich Krause

------------------
'95 Z-28 383: Vortech, nitrous, etc.
AIM: rstevenkrause

 

if 415 iws the limit, how did some of the magazines a few years ago get a gen1 sbc to 454?

 

Tall Deck Block

 

Along with a tall deck such as a 9.3 deck the cam position is raised .391 or .400 to releave the clearance issues..

what makes me wonder is why people build these combos with too small full zoot 23 degree heads..If a big block warrants 400+CFM intake why would a 454 small block be okay with less than that..I had this disscussion with a guy that i bought a set of brodix canted valves and SB2s from last year..

Also when i think about a build up of a stroker the next time i will buiy an aftermarket block..Locally in pa teh standard
bore/hone,clean plugs and cam bearings can run up to 700 smacks..Add to that the cost of splayed caps 350-400 with parts,clearancing for the stroke 100-400 one would think im stupid to pay the extra cash for a block that a lot stronger and newer..

[This message has been edited by LT1 1980 malibu (edited September 11, 2002).]

 

This is good info guys, thanks! Keep it coming!

OK, the head and valve issue is another thing I had not thought about too much. I currently have a pretty decent set of Sportsman II 200cc runner, 64cc chamber heads with 2.02 and 1.60 valves. I was hoping I could continue to use them on a stroker that is blown. But now I'm not sure. These may be too small on a stroker engine. If I have to get another set of heads, that adds a major amount to the budget. However, I do have the go ahead from the wife to build the engine I want, so I am also thinking of an aftermarket block such as a Motown. That would solve the cylinder thickness problems and the crankshaft clearancing problems. If I do get the aftermarket block I will go with the large bore, since for a blown engine I was told I would have to get custom made pistons anyway. That just leaves the stroke open, as the Motown will accept up to 4.0" without machining, and more with machining so I am told. But my funds are not unlimited, so a custom stroke crank is not where I want to go.

I was concerned about a stroker not being able to get as much RPM but Richs' post made some sense out of that. The FI is not so dependent on RPM, so a stroker held to 6000 RPM should be sufficient? And then, the extra cubes of the stroker will give that low end torque to get you moving and powering out of the corners?

What about rod length? In a blown application, you need more piston thickness at the ring lands, correct? Doesn't a longer rod impinge on that area?


[This message has been edited by 89WS6L98 (edited September 11, 2002).]