Inliners International Forums General Discussion Hi Performance 292 x 250 Jisaw

Hi Guys

i will be ordering new rods and and i´m searching for a good block, well i got an ideia....

292 block +
longer rods (250 longer rods)+
250 crank

= 250 with longer rods, which would give a better r/l

what do you think of the ideia? mixing the 292 block with a 250 crank and longer 250 rods would work fine?

Now why would you want to turn a 292(block) into a 250 motor? by useing a 250 crank in a 292 block?
You would end up with a tall deck 250 motor,I'm sure it may??? buzz a little faster???But I can not see why you would want to give up the extra 42 cubes.And I think you would need more then a 6in rod to get the piston to top dead of the block.Seeing that the 292 is a 1 3/4 taller then a 250.

Just my 2cent woundering???

Larry

i talked to some guys and they do this mix with VW engines! they use a taller block, and longer rods and a "stock" lenght crank. they say this gives the engine a better r/l (radius of the crank stroke divided by the lenght of the rods) which means much less stress to the cilinder wall and more longevity to the engine. sure i would need to order longer than 6.00" rods!!!

Edy, I couldn't find a 7.0 inch rod to put in my 292 so I could use 283 or 305 pistons. The 250 has a stroke of 3.53, the 292 is 4.12 with a rod length of 4.76. Guessing that the rod length of the 250 is about 4.1 approx. add 1.75 for the extra block height , you would need at least a 5.85 rod. One of the reasons I couldn't find 7.0 rod for the 292 was all the big blocks and small blocks use a narrow rod end on the crank because they pair rods on the same journal. My 2 cents, if that.

Larry

PS if you find some 7.0 rods let me know please.

No worries Edy I fixed your two extra Posts.
Ok I kinda understand what your saying.

Larry

so, the 250 crank will match the 292 block?


Edy

lgraffin

i'm going to order custom rods, so the lenght would not be a problem, i would just need to order the longest rod possible!


Edy

Edy,
I think it would be a waste of time & money to build an engine like this.
But,,,,, to each his own :-)
The rod to stroke ratio is fine on a stock 250 block & crank.
The cylinder walls are not streesed that much.

A bad rod to stroke ratio would be like a SBC 400
3.75" stroke, 5.6" rod IIRC? (liitle help)

On those engine blocks,, the cylinder walls do take more stress from this bad ratio,esp in a high performance application

W/a 292 block you will just be adding extra,w/no performance gain, other than the block is a little more durable/stronger in the front headbolt area.

If you want the 250 crank to be stronger,, you can have the rod journals turned down smaller than 2" like to 1.9" or so,,in order to have big radius's on each side of the rod journal & run custom rods.

Now,since you can have cranks made there in Brazil,,, I would have a destroked 292 crank, like 4.0" stroke,but doing that,you will be losing engine size,but this will allow you to run higher RPM than (& potentionally make more HP)w/a standard 292 stroke of 4.120

I am not a big fan of the 292's (4.120")big stroke for racing & high RPM.

Sure you can turn some RPM w/a 292, but,,, most will agree,, for racing the 250's stroke is more durable.

Now for a normally aspirated street engine, go w/the cubic inches.
But for your turbo application, run a 250 & just crank up the boost!! Two cents,if you can kinda understand what I said? :-)

MBHD

Hank

Thanx for your two cents!! :-)

i will have to give up the ideia anyway! i´ve found that the Brazilians 292´s have the main journals different from the americans 292s. so the 250 cranks (which are the same as the americans) won´t fit in the brazilians 292 (thx the Brazilian GM!!!) very sad this!!!
a friend of mine said to use a longer rod and a piston with a higher position pin, it would give a better r/l too! i will do some math and what can be done!!! ;-)


Edy

Edy,

As far as the 250 goes, you all are lucky in Brazil with the '95 to '98 engine. Those engines have a more modern piston/rod design with the longer 6.00" length rod and piston with the shorter compression height, approximately 1.355" (higher wrist pin location). The USA 250 engines have the older piston design with the taller compression height of 1.655", together with a shorter rod of 5.70".

Any way we can import some of those '95 to '98 piston and rod assemblies (with rings, wrist pins, bearings) 0.030" overbore at a reasonable price to the USA? Who makes these pistons in Brazil? I tried General Motors in the USA, no assistance and they would not extent any effort on their part for contacts in Brazil.

Hi Winter!!

you can import, it's very easy to find rods, piston and bearings here (stock parts, not forged) i'm not sure if you can order directly from the dealer (i dont know if the speak english :-) ) well, i will give you a link to the biggest dealer parts in Brazil. you can try with them, if you dont have lucky, you can email me, and can help you on that!

the link is

http://acciolygm.bigsolutionsidc.com.br/

Thanks Edy,

I will look into the website.

Do it the other way 250 block/292 crank/ maybe 283/327/rods. Somewhere I heard the 153 four cyl rods will work. The v/8 rods may line up a little off center in the pistons...what the heck !!! shift down and "GAG IT"...SCRAP

doing the 292 crank in a 250 takes more work then one thinks. It also puts more load on the cyl.walls because of the longger stroke. and to do that type of conversion it would run you around 1200 bucks.Custom pistons and the crank needs to be machined. And it is also my understanding so does the block to clear the 292s counter weights.

People in cicle track have used V-8 rods, but doing so, you will loose oil pressure,a lot of extra oil flinging around the crank,cam, there fore slowing down things a bit.AKA loosing power.

MBHD

I'm doing a 4.120 crank in the short deck block with 5.564 rods (400).....the rod ratio comes out to be 1.4 which is pretty low BUT this engine is being built for the street and will never see above 4500 .....side loading becomes more of a problem at high r.p.m.....the oil flow is not an issue if the clearance on the crank and bearing are on the low side...flow x resistance = pressure...the oil flow will be controlled by the bearing to journal clearance not the rod side clearance...counterweights on the crank require severe reduction but the crank balances with out bob-weights anyway so hopefully it will come in after modification...just an experiment for a c-10 with a 3.07 gear and an s-10 five speed.

Yes. you will have more oil flow if your rod side clearance is more than what it supposed to be, sorry to burst that thought.
MBHD

Guess I wasn't too clear...the rod side clearance will be controlled...even with pressed pins and low r.p.m I don't want the rod snaking around on the journal...there are button head pins that can be installed to correct the side clearance but that does leave more area for flow on the sides ...this is not a high rpm engine so the throw-off shouldn't be a problem...as you mentioned earlier that stroke length wasn't designed for high r.p.m...it can be done but it isn't cheap...I'm looking for torque at low rpm,figures out at around 1850 r.p.m.@ 70 m.p.h....I have a 307 piston 250 with 1.84 305 valves in it now that sings pretty good with 3.73's at high way speeds..the gear change is going in with the new engine.... thanks

It should be a a good low RPM engine engine when you get it done.
Let us know how it turns out.

Installing some bolt in lumps?,,,,that will give you even more low end torque,,, & more power everywhere.

MBHD

Hank, I've thought about the lumps....from what I can tell they are an improvement in any application...the head I've got now just has the boss streamlined and a some bowl work...it will probably get freshened and swapped over for a while....I'm not much at the picture thing but will keep you posted...maybe I can get one of my students to show me how to post pictures; I'm sure they have a better handle on it! Fats