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A "TRUE"305

5K views 33 replies 9 participants last post by  305mouse 
#1 ·
I have a 76 305 that i want to make a muscle motor with.I hear people talk about there bad 305 stroked to a 331.
To me its not a 305 anymore. I seen one true 305 muscle motor at a track in northern IA.the bottom half was completely
Stock including pistons,but the upper half was set up real nice & had the right gear/tire combo.It was in a 83 cutlass that he
Drove to & from the track.I wanted to get more info from the guy,but didnt get a chance to,but he was turning times of 13.50s.
The thumpstick was huge or sounded like it anyway.I remember looking in at the tach.& it was pulsing between 1000&1200.that's,
How i want to build my 305.Any clues to a formula like that would be awsome!
Thanks! :confused:
 
#4 ·
VERY basically you need enough compression ratio to support the camshaft's duration/overlap and enough valve lift/cylinder head flow to allow the engine to make power in the RPM range you've targeted. Then it's a matter of feeding the heads w/enough air/fuel and exhausting the remains.

Hooking that power up to the track is as important as making the power in the first place, so the vehicle weight, torque converter stall speed, rear gear ratio, tires and suspension/shocks all come into play.

You might want to start by doing a search on this site for 305 builds. There are MANY threads on them.
 
#6 ·
Ok guys n gals,my buddy was on his fourm & asked for a wicked combo for a stock bottom half & got a hit from a guy in Cali.that run this combo for his stop light to stop light racer,
Tell me what you think.cam;234/244-488/510 110lobe sep. Intake;Weiand highrise dual plane. Carb;Holley600 vac.secd. Double roller chain,1.6 rockers(not roller).Super Comp.full size headers,
2.5"pipes with FlowMaster 40s(no cats),350 trany with 3200/3500 stall. 488 gears.This is in a 81 impala 2dr. Rear tires are 215/60/15.He said he was on YouTube in 09 running against a 99 camaro 5.7
& beat it by a half car!(1/8mile).Please let me know,i would like to start building soon.
Thanks Again! :D
 
#7 ·
305mouse said:
Do some 305s come stock with flat top pistons?I pulled mine apart & the pistons are flat tops?
They have 2 half moon shapes in the tops?
I think there were a few 305's w/FT pistons (w/four "eyebrow"-type valve reliefs) but most came w/a dish and the four eyebrow reliefs.

Your pistons sound like they're aftermarket if they have just two valve reliefs per piston. If you look closely at the top of a piston you may be able to see a part number and an oversize marking like "020" or "030".


COMMON 305 DISHED PISTON

cam;234/244-488/510 110lobe sep.
To use that much cam effectively in a 305 will require heavily modified production 305 heads (ported, 1.94" valves fitted, new valve springs at a minimum), modified Vortec production heads (guide boss shortened and cut for seals, new springs, milled deck) or aftermarket heads. You might also consider the old small chamber "fuelie"-type head- but I wouldn't favor them over the Vortec or aftermarket heads. Any production head can benefit from screw in studs and guideplates. I would choose a cam that had the specs I wanted w/1.5 rockers instead of using 1.6 rockers.
 
#8 ·
Cobalt,ya that pic.you have posted is what mine look like.I thouhgt the 4eyebrows made 2 circls.sorry about that!...Wow,that's alot of work for that cam set up.Well,back to the drawing board.
Darn,my auto tech.teacher must of been right by saying im trying to polish a turd!lol...im not giving up!He told me one time to put 350 rods in it to shorten the stroke? Sound right.What makes a 305ho?
My older sister had a 76-77nova i think it was a ss or rs & had a 305ho.It was a tire burner!
 
#9 ·
305mouse said:
Cobalt,ya that pic.you have posted is what mine look like.I thouhgt the 4eyebrows made 2 circls.sorry about that!...Wow,that's alot of work for that cam set up.Well,back to the drawing board.
Darn,my auto tech.teacher must of been right by saying im trying to polish a turd!lol...im not giving up!He told me one time to put 350 rods in it to shorten the stroke? Sound right.What makes a 305ho?
My older sister had a 76-77nova i think it was a ss or rs & had a 305ho.It was a tire burner!
The bottom end of your engine- all the way up to the pistons- is identical to a 350. The pistons of a 305 and the bores in the 305 block (that cannot be bored to the size of a 350, btw- in case you were thinking that way ;) ) are about 1/4" smaller than the 350. The 305's bore is 3.736", the 350's bore is 4.00". BOTH use the same 3.480" stroke crankshaft.

Changing the rod length doesn't have any effect on the engine displacement. The displacement can change two ways- bore and stroke.

The 305 HO engine used more CR and IIRC a bigger cam and had heads w/1.84" intake valves instead of 1.72" intakes used on the lower output 305's. There may have been other differences, you can check on that through google or maybe someone here will chime in.
 
#13 · (Edited)
cobalt327 said:
BOTH use the same 3.480" stroke crankshaft.
True they both have the same stroke but the cranks aren't quite the same. The 305 crankshaft uses smaller counterweights because of the smaller pistons. That's not to say that interchanging cranks wouldn't work, but they're not the same.

305mouse said:
Ive learned more in one day here than 3yrs. Of highschool tech.class.
It sounds to me like your school needs to find another auto shop teacher.

Here's an article about a 370+ hp 305 build: http://www.popularhotrodding.com/en...s_305_chevy_engine_blocks/engine_testing.html

Something to consider though is that if you were to build an otherwise identical 350 you're going to end up with over 400hp. That's why fewer people are building small displacement V8s and 383s, 400s, 454s and 500+ ci engines are becoming more and more popular. More cubes from an otherwise identical engine is darn near free horsepower.
 
#15 ·
Ya,the more i think about it i might jump on that 350 with 305 heads. My shop teacher was hard to understand,he is a big Mopar guy,infact running a plymouth arrow with a 501 indy motor.
We went to the track as a class & watched him lay down 8.20s(1/4mi.),but cant help me with my sbc?
 
#18 ·
By the way 2 good points made,the whole car has to be setup right as well & the 11sec.305s that were spoke of; that was the class that guy with the cutlass was in(i think).if i remember that class had to run iron heads & complete stock bottom half.Street elm? Anyway its proof the 305 can run hard without boring.Is the 350 with 305 heads a good combo? If i remember right,doesnt that push the comp.to 10?
 
#19 ·
Blazin72 said:
True they both have the same stroke...
Which was the sole point I was making. But since you brought it up,
The 305 crankshaft uses smaller counterweights ...
The difference isn't in the counterweight size, it's in the weight. Even w/a different bobweight, as long as the rods and pistons are weight matched the difference will only be in the balance factor, either over- or under-balanced from the 50% "norm".

The crankshafts used in 305 engines w/2-piece RMS were also used in 350's and carried identical casting numbers (the most common is the 2-piece RMS c/n 442):

3932442 305/350 69-85 2.45/2.10 3.48 Nodular Iron
14088535 305/350 86 & UP 2.45/2.10 3.48 Nodular Iron One piece seal

A crank used solely by the 305 wasn't until '86 and possibly beyond, it was a 1-piece RMS crank c/n 14088526.
 
#20 ·
305mouse said:
Is the 350 with 305 heads a good combo?
It is one way to go. Mostly done where the budget or entry-level racing class restraints are such that using better heads cannot be done. Suffice for me to say that there are other, better heads to use than a set of reworked 305 heads- and that's the main point, here: stock 305 heads are just about worthless on a 350. Unless you have the tools, skills to rework the 305 heads yourself, using a better head from the get-go would be my recommendation.

That said, I'd much rather see you using an L31 5.7L Vortec long block as the foundation- good heads, 1-piece RMS and a roller camshaft set-up all rolled into one.
 
#23 ·
305mouse said:
Ok,what year/make should i look for this L31?
The L31 Vortec was used in trucks and SUV's ‘96-‘00 (or 2002, depending on where you look). VIN "R" is a Vortec but engines can be swapped around, so better to look at the block to see that it's roller cam-equipped (an easy way to tell is to check the length of a pushrod- roller engines are 7.2" long, flat tappet engines are 7.8" long).

1986-Up 5.7L Roller Cam/Lifters Block Casting Numbers:
10243880
14011148
14088526
14093638 (one guy says has one w/o tapped holes, bosses were there).

1986-Up 5.7L flat tappet (i.e. non-roller) Block Casting Numbers:
10054727
14079287
14088548
14101148.
These flat tappet blocks may have the provisions for a roller cam (i.e. bosses cast in and tapped for the spider, tapped holes for the cam plate, etc.)- but very well may not be so equipped- but these blocks will have a flat tappet cam and non-roller lifters, no spider, etc.

There is a flat tappet block and a roller block that both end with the numbers 148. 14101148 is a flat tappet block, 14011148 is a roller cam block.

Some blocks came machined for a mechanical fuel pump. Others (most) have either partial or no machining done to use a mechanical F/P.

A member here posted the following regarding the fuel pump (sorry, I don't recall the name to give proper credit):
"All of the 638's that I've seen (not that many, 5 or 6) have had the pump rod hole drilled.
I've seen 880s both ways, and both 14011148 I've seen were undrilled."


Do i have to use a"vortec" intake?,i would like to use a carb not TBI/FI. We have a 89 gmc truck out back were i work,has a 5.7tbi with roller rockers(factory i think?) would that be a L31
The L31 Vortec heads use a carbed intake made for just them- earlier Gen 1 SBC intakes will not fit.

The '89 truck engine may have a roller cam and lifters- or at least have the tapped bosses for mounting up the spider and cam thrust plate- BUT some '86-'95 blocks are cast without the bosses and are not able to use the OEM roller cam/lifters w/o a lot of work. Basically not worth fooling with, IMO.

None of these engines came w/roller rockers from the factory, so if that '89 engine has them, they're aftermarket. This short block would be fine to build with, but you'd need to check the c/n of the heads.
 
#24 ·
Ok,with all your great info i found a motor at the swap meet today! I cant bellive it snowed like crazy!, anyway i found motor/trany & the computer for $650. It came out of a 97 chevy 1500. 117k on it. Im so pumped! Now...the build. Thanks again. :thumbup:
 
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