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chevy 250 performance build


johny89
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hello,

i have a 250 with integrated head which needs a rebuild, while I'm at it i want to make it a performance rebuild. Car is a 65 impala with a three on the tree gearnox, gearbox will stay the same and car needs to be driveable on the streets,

I was thinking of milling the headers of of the integrated head but want to be sure i can still add a custom header after i did it. is there enough room left for mounting bolts or didn't anyone ever gone this far.

+ extra tips on what parts to use are always welcome.

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If it were me I wouldn't spend money on the 250 trying to get a little bit better performance. I would think the machine shop time to work the head to accept aftermarket manifolds would not be inexpensive. I would replace it with a stock 350 or 400 small block. Chevy small blocks are plentiful and cheap. That can be done with all stock parts available at NAPA or other big parts stores. I would upgrade the front brakes to disc which can also be done with later model stock parts. I think you would be much happier with the improved performance over the 250.

Check out several Chevy performance websites and you can get advice as to what stock parts are needed to make the engine swap and brake upgrade. Also check the HAMB at www.jalopyjournal.com.

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hello, be thinking of someone sugesting a 350/400 and i apreciate the help but for safety inspections (belgium) i can only stick with the 250 (no matter how much hps its got.) since that is the only choice i have i consider it as a challenge to build a performance 250, as for the disc brakes: i already have some parts, still need to find the time installing...

I know a guy who has a machine shop, will ask him today what he think it would cost, my guess between 100 and 300 so i can live with that...

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Johny

Sorry, I didn't realize that you are in Belgium. Below is a link to a site that says the best and easiest way to increase the performance of your 250 is to use a head from a 292 and aftermarket intake and exhaust manifolds made for 194, 230 and 250 engines. New model 292's were found in trucks and buses from 1975 through 1990. If you can't find a 292 head in Europe try this used parts company http://www.justchevytrucks.com, or, this parts locator service http://www.uneedapart.com/used-truck-parts/. I don't know about overseas shipments, but, domestically used auto parts are the lowest tariff rate. You may have to find an export agent to do the paperwork for customs and arrange the shipment.

http://www.crankshaftcoalition.com/wiki/Building_an_inline_6_Chevy_250_engine

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you're right but it had this engine in it when it was imported so that is the one on my papers (even the year of construction is wrong on them) but i can't change that anymore so i have to stick with the integrated head,

good new might have found a 292 head for 100dollars about 3hours from where i live.

any suggestions on cam timing, intake and headers to go with? should i change the valves in the head? looking to get +-200hp, more is welcome but thats my minimal goal.

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It sounds like you have a 250, I don't think the 292 came with the integrated head. I believe the 250 and the 292 are same, but 292 has more stroke hence the higher deck, The 292's side covers are about 6" tall, the 250's 4. If you buy that head check it for cracks in combustion chambers. Clifford intake might be the best for a 4bbl, but don't go above 550 cfm

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it is a 250, will a 250 cam fit for a 292 head?

was thinking about following cam:http://www.summitracing.com/int/parts/cca-cl61-233-4/overview/make/chevrolet think this is not too extreme to start of with.

this intake manifold: http://www.summitracing.com/int/parts/ofy-5416-lk/overview/make/chevrolet

this carb: http://www.summitracing.com/int/parts/hly-0-8007/overview/

and these headers: http://www.cliffordperformance.net/Merchant2/merchant.mvc?Screen=PROD&Store_Code=CP&Product_Code=52-0011&Category_Code=C250

still need to choose an ignition system + does an original fuel pump deliver enough fuel for my needs?

what more than rebuilding the engine (new piston rings, bearings etc...) should be done?

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Johny

The difference between the 250 and 292 is the bore and stroke and the integrated head and manifolds of the 250. The cam should work with the 292 head but you will have to get a set of 292 push rods as the 250 push rods will be too short. So long as the ratio of the valve rocker arms on the 292 head are the same as those of the 250 the valve timing will not be effected.

Change the head, get a "performance" cam kit (includes new lifters) from a store like Summit or from a cam company like Comp Cams or Lunati Cams, a set of 292 push rods, after market intake and exhaust manifolds. You can select a new intake that will use your current carburetor, or, a new 2 of 4 barrel carburetor, depending how much you want to spend on a carburetor. Remember that a 250 cubic inch engine will not require a high volume carburetor. About 300 to 350 CFM is the max that a 250 can handle. This can easily be met by several 2 barrel carbs. If your fuel pump is in good condition it should be more than sufficient for your upgraded engine.

Before you tear down your 250, perform a compression check on your engine and if it has good compression and no fast leak down of the pressures, fairly even pressures from cylinder to cylinder, then I would not do anything to the lower part of the engine. Since you are buying a 292 head, I would have a "valve job" performed on the head.

The stock Chevy high energy electronic ignition (HEI) should be more than sufficient for a stock compression engine. High performance ignitions are for engines with high compression and high fuel to air ratio which such combination requires a higher secondary voltage to ignite the fuel air mixture.

Edited by Bob Call (see edit history)
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so how much of the head can i take of before i need a high performance ignition?

if i understand correctly you suggest not changing the main bearings etc?

i know my engine has a leaky freeze plug and a leaking main seal. if the compression is good just change these out?

i now have an original 2bbl rochester varajet, and an orignal 1barrel (1977 camaro)

I need to rebuild one of the old carbs or i just buy a new one (not such a huge difference i think.

how much do you think it will be getting with the suggested upgrades?

thanks for the advice already

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Johny

I would check the head to be sure it flat on the mating surface to the block in order to have a good seal with the head gasket. The machine shop can check this with a straight edge. If it is not flat have it surface milled enough to make it flat. I don't believe you can mill enough off the head to make a real difference in the compression ratio. That is best done with high compression pistons. Next best is a turbocharger but that is getting into some real money. You don't need to spend money on a new ignition system.

If the compression test is good and the oil pressure is good when the engine is at operating temperature, then I would not get into changing bearings. If, the oil pressure is low at operating temperature then the main bearing are probably worn. If that is the case pull the engine and tear it down. Take lots of pictures so you will know how to put everything back together. If you don't have one, get a shop manual that covers a model year with both the 250 and 292 engines. Have the machine shop to check the cylinder bores and crankshaft. If the cylinders are not out of round and not excessively worn they can be honed and new piston rings installed. If the crankshaft journals are round and not excessively worn you can replace the rod and main bearings. If it is out of round or excessively worn, it needs to be reground by the machine shop and the correct undersize rod and main bearings installed. If the cylinders need re-boring, then you can check on the price difference between stock replacement pistons and high compression pistons.

Freeze plugs should be replaced as they are cheap. I don't know about this generation of Chevy sixes, but, a lot of engines the rear main bearing oil seal can be changed by removing the oil pan and main bearing cap. Another thing covered in a shop manual.

I would check into another 2 barrel carb to replace the Varajet.

There is an old saying among Hot Rodders, "going fast costs money, how fast do you want to go?" Check pricing of the parts you want or need and get an estimate of machine shop time. Total those estimates and add 50%. The mechanic I take my cars to says building a moderate performance engine costs at least $1,000 per cylinder.

Edited by Bob Call (see edit history)
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