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Discussion Starter · #1 ·
Hello all, I have a rebuilt 305 on a stand waiting to go into my truck and am very curious as to what yall think it will do performance whise. It's an all stock 1978 305 sbc it will have a comp xe250h cam in it, and edlbrock performer rpm intake and a 600 - 650 holley, and longtubes. What kinda power should I expect? Will I see a noticeable gain from the stock tbi L03? And is the xe250h a good cam for this application (will be running stock 700r4 converter for now) if not what cam would you guys recommend. I want a rough choppy idle but I know a big cam isn't ideal in this case any help is greatly appreciated
BTW I understand a 350 will perform better but I bought it cheap already rebuilt.
 

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Wrench Turner
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Do you know which parts were used for the rebuild? Is it over bored?Decked?Piston type, volume, compression hgt? Headgasket thickness? That's the problem with buying a rebuilt motor.More likely than not, shorter rebuilders pistons were used that sit farther down the bore than stock, combined with a thick rebuilders gasket that came in a rebuild kit.This all lowers compression & hurts power & detonation resistance. You likely have less than 8:1 compression. Which heads are on the motor? Casting #?
That cam is about as large as you can go & still have any kind of performance. It will not have any lope.In a properly built 305, with adequate compression & supporting parts, that combo could easily make 275 HP.If it's built as I described above, maybe 210 HP & not be very efficient at that.Most 305 heads are done by 4000 to 4500 rpm, so, using a cam with a higher power range won't help.Only make things worse.DO NOT PUT A THUMPER CAM in this motor.
The best thing you can do to see & realize more from this, especially in that heavy truck, is to lower your rear gearing.This will give you the most bang for money spent.
Rebuilt can mean different things to different ppl.It could have honed & put together with the same pistons w/ new rings & bearings, or, it could have been properly bored machined & assembled back to spec.Do you know what you have?
 

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Wrench Turner
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A thumper cam is good if you want that sound without a truly big cam

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Good for what? LOL.
The smallest Thumper cam available for his motor is a 227/241 @ .050.That would be a humongus cam in a 305,especially if compression is already low.It will have some lope to it alrite,but,that's all it would have.
 

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Wrench Turner
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Hello all, I have a rebuilt 305 on a stand waiting to go into my truck and am very curious as to what yall think it will do performance whise. It's an all stock 1978 305 sbc it will have a comp xe250h cam in it, and edlbrock performer rpm intake and a 600 - 650 holley, and longtubes. What kinda power should I expect? Will I see a noticeable gain from the stock tbi L03? And is the xe250h a good cam for this application (will be running stock 700r4 converter for now) if not what cam would you guys recommend. I want a rough choppy idle but I know a big cam isn't ideal in this case any help is greatly appreciated
BTW I understand a 350 will perform better but I bought it cheap already rebuilt.
Also,I'm confused.You say the motor is a 1978,yet you make reference to the L03 305 which didn't come about until 87/88.The L03 motor could be a roller cam motor,if from a car,or,it could be a flat tappet cam,if,from a truck.Do you know for sure which motor you have? Intakes & flywheels will also be different between the 1978 305 & the later model L03,as in 1978,you would have a 2 pc rear seal.The L03 will be a 1 pc rear seal.You really need to know exactly what you have before you start buying parts.
 

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Google "Tunnel Ram 406"
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Hello all, I have a rebuilt 305 on a stand waiting to go into my truck and am very curious as to what yall think it will do performance whise. It's an all stock 1978 305 sbc it will have a comp xe250h cam in it, and edlbrock performer rpm intake and a 600 - 650 holley, and longtubes. What kinda power should I expect? Will I see a noticeable gain from the stock tbi L03? And is the xe250h a good cam for this application (will be running stock 700r4 converter for now) if not what cam would you guys recommend. I want a rough choppy idle but I know a big cam isn't ideal in this case any help is greatly appreciated
BTW I understand a 350 will perform better but I bought it cheap already rebuilt.
Big cam, Big trouble, Not good.
 

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Discussion Starter · #10 ·
My boss was short on pay and gave me the motor It's all stock. I tore it apart and it's all shiny and brand new inside I don't know what size cam it has, I believe it's aftermarket because it has purple paint on it I could be wrong though. IL be starting a 350 build soon I have domed pistons the 350. This 305 is to replace the oil burning 305 thats in my 1990 swb chevy. I just want to know about how much power I can expect. I used a felpro gasket kit to put it back together.
My boss Daryl Peveto has been building cars all his life so I trust that the motor is in spec
 

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Discussion Starter · #11 ·
And the L03 is what's in my 1990 c1500 the motor I have on the stand is a 1978. It's actually got 2 different casting #s on the heads. Although they are different heads my research told me they both have same size combustion chambers, intake and exaust valves. 1.50 on the exaust and 1.70 on the intake I believe they were 58cc comb. Chambers
 

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Wrench Turner
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And the L03 is what's in my 1990 c1500 the motor I have on the stand is a 1978. It's actually got 2 different casting #s on the heads. Although they are different heads my research told me they both have same size combustion chambers, intake and exaust valves. 1.50 on the exaust and 1.70 on the intake I believe they were 58cc comb. Chambers
What are the casting#'s. As I mentioned ealier,the 1978 motor will be a 2 pc rear seal motor.The motor in your truck is a 1 pc rear seal & uses a different flexplate.The bolt pattern on the intake between the 2 motors is also different,tho,not really a big deal.
Saying the motor is "stock",still doesn't tell us very much.Has it been bored?some 305's came with flat tops & 9.5:1 compression.some only had 8:1.What type if pistons were used & how far down the bore do they sit at TDC.Headgaskets can range in thickness from .015" to over .050".All this needs to be known.You've also got some work to convert this thing to a carb.
You need to know exactly what you have before you wisely choose a cam,or,much of anything else.With those small valve heads,this motor will done by 4000 rpm.
As for the 350 build,domed pistons are not the best choice.They are a necessary evil when using large chamber heads to raise compression.You will be much better off with small chamber heads & a flat top piston.Don't base your 350 build around a set of domed pistons.
 

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Wrench Turner
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Depending on the parts used & the quality of the assembly,power could range anywhere from 140 HP to 300.Just a pick a number.
I'm not trying to be sarcastic, but, with no info provided, there's no way anyone can provide an estimate anywhere near reliable.You've failed to provide answers to the questions asked.
 

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Discussion Starter · #14 ·
Dished pistons idk how far down they sat seemed to be level with the top of the block i know thats probably not technical enough and il have to find out the head gasket thickness maybe it says it on the box. IL post casting number soon next time I get a chance to look
 

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Wrench Turner
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We need to know if the cylinders have been bored & to what size?Which pistons were used,part# description,etc. Headgasket thickness & if the block was decked,or,not.Along with the head casting#.
 

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Discussion Starter · #18 ·
Let's say it's back to factory spec compression ratio and everything with and edlebrock performer rpm intake 600 holley, hei, a comp XE250H cam, and longtubes headers true duel to a duel in duel out Flowmaster. The heads are 58cc with 1.70 intake and 1.50 exaust IIRC. just give me a rough estimate. I'm looking for an improvement over stock. A ball park figure of what to expect would be nice
 

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Wrench Turner
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A really well tuned stock LG4 will put down approx 225 HP with a Qjet, longtubes, & a good exhaust system. IF & I repeat, IF, this thing is assembled properly & within stock specs & the cam you listed, your looking at approx 250 HP, with spot on tuning.
 
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