n8sz28

does anyone know if its worth putting on aftermarket runners like slp performance to give the 305 a little more horsepower? if so can anyone estimate a quarter mile difference and do you have to install headers to get the full effect?

merc3065

Best thing to do is to match parts on intake with parts on exhaust. If you get a better flowing intake, you want to get a better flowing exhaust.

You will notice a little bit of a difference on a stock 305 with some aftermarket runners. Match that with headers and you'll be cookin with gas.

If you get a cold air kit and a bigger TB (nothing crazy) and go with a new intake manifold that flows better, your heads will start becoming a big restriction. Then you get a new set of heads. Then you match the cam with the heads and go with a 3" exhaust cat back, etc etc

Just match parts with parts to get an overall well functioning motor. Any restrictions in the system and you impede performance.

If you are looking to pick up a few horsepower, get the runners, and while the intake plenum is off, gasket match the plenum to the runners and remove the castings off the inside of it to help airflow.

smithtc

iTrader: (5)

Depends...on other modifications and what you are ultimately after. It will lessen the overall intake restriction.

GETTING YOUR Intake....... length ....... port in -- out
Stock GM Base--- 6.375"------ 1.47"- 1.96x1.2
TPiS base------ -6.125"------ 1.75"- 2.09x1.28
Accel base----- -6.125"------ 1.75"- 2.09x1.28
Holley base------- 6” runner 2.3”- 1.9”x 1.23 (2.337 sq inches)
Runners
Stock TPI----- -- 7.250"------1.470" round(1.70 sq inchs)
SLP ----------- - 6.625"------1.600" round (2.01 sq inchs)
Accel LTR------- 6.625"------1.615" round (2.05 sq inchs)
TPiS----------- 7.625"------1.660" round (2.168 sq inchs)
Mini ram -----3.5”
LT1 ----------3”

Runners (measured individually)
Stock....................203.17 cfm
ACCEL................242.02 cfm
Extrude/ACCEL...275.83 cfm
Super Ram............289.18 cfm

Intake manifold with 3/8 inch radiused intlet
.............................222.45 cfm
Holley stealth ram ………..275cfm

Stock intake manifold with runner
Stock....................198.72 cfm
ACCEL................213.52 cfm
Extrude/ACCEL....217.11 cfm
Super Ram............220.67 cfm
Holley stealth ram …..275cfm

ACCEL Hi-Flow intake manifold with 3/8 inch
radiused inlet.........251.51 cfm
ACCEL Hi-Flow intake manifold with runner
Stock....................215.83 cfm
ACCEL................232.53 cfm
Extrude/ACCEL....243.21 cfm
Super Ram............240.24 cfm
Extrude-Honed ACCEL Hi-Flow intake
manifold with 3/8 inch radiused inlet
............................275.83 cfm
Extrude-Honed ACCEL Hi-Flow intake
manifold with ACCEL runner
............................266.94 cfm
Edelbrock Performer RPM manifold
(Stock)..................286.51 cfm
Edelbrock Victor Jr.
.............................275.24 cfm

HOLLEY STEALTH RAM
Stock…………………………… 275cfm
Ported…………………………..300cfm
Runner lengths
Stock tpi manifold 8” runners 11.25”, cylinder head 6” total 25.25”
Accel super ram manifold 8” runners 7” cylinder head 6” total 21”
Holley stealth ram manifold 6.26” ” cylinder head 6” total 12.26”
Edelbrock performer RPM runners 6” ” cylinder head 6” total 12”
Edelbrock vic jr , runner length 5.5” ” ” cylinder head 6” total 11.5”


Depends on how big a restriction it is at this point. If your car is stock, and this is the modification you choose to do, you will not see any noticeable increase in performance. You will notice an increase in performance with headers and overall exhaust improvements. What will the runners add to this?...Probably very little unless other intake modifications are done as well.

After exhaust, it is My Opinion that your heads will be the next major restriction. I plan to take a completely stock 5-Speed GTA and begin running it down the track. The heads will actually be my 1st modification (engine wise), before exhaust...port & polish keeping the stock valve sizes.

DuronClocker

iTrader: (1)

Definitely do exhaust first. Bigger runners won't give you a whole lot on an other-wise stock 305. Headers and full 3" cat-back with a high-flow cat (or cat delete, pending local laws) will make a noticeable gain. My peanut-cammed 305 was able to pull to around 5500RPM after I installed headers. Your '85 motor has a better cam than my '88 did, which means your heads will definitely be the next restriction after exhaust.

On most 305s, I'd say go headers/exhaust, and then a cam/heads. If they don't want to go through buying new heads and installing them, then definitely a cam. Most 305s cam with really tiny cams that held them back real bad. Your cam is a bit better though.

Headers/exhaust --> Heads --> Cam

Though it might make most sense to do heads and cam at the same time..

Also, a bigger throttle body won't help you, especially with a 305, until you are making a lot of power...more than most 305s ever make.

DuronClocker

iTrader: (1)

And then before you really need new runners, you should port the stock plenum a lot. There is a lot that can be ground away to gain a lot of flow. Then look at the intake base manifold. That can be gasket-matched to flow a decent amount better as well.

85rocker

I agree

I would not use runners on a 305 without exhaust, cam and head work first.

I did SLPs on a '91 LB9 without first doing cam and headers or head work and figured it was a huge flop -- and that was after countless hours of porting... barely noticeable performance gains. Very disappointing.

With an LB9 do exhaust then do heads and cam.

subroc

iTrader: (2)

On the same topic..how much power can be obtained by porting and siamesing the stock runners, plenum, and base?

85rocker

Some very skilled individuals have taken to this kind of porting and had reasonable success. 25hp if I recall correctly.

Others, perhaps less skilled, have found the results not worth the effort and I know of one person who saw zero gains from siamesing.

I find it interesting the after market runners with the best results are consistently LTR's (eg: AS&M) and not siamesed pieces.

my 2 cents

1MeanZ

iTrader: (9)

What is your performance goal? TunedPort335 is going mid 13s at 98mph with stock heads and intake. I am going high 13s because I can't hook but my car consistently trapped 100.5mph with ported stock stuff. A 305 is 13% smaller than a 350. Theoretically I think it should only need 87% of what a 350 would need at a given rpm. L98s can go high 13s with stock stuff, I wouldnt think ported stock TPI would not hurt a 305 unless you were runnin low 13s or were trapping over 102mph. The problem with all this is that I have not seen documented results from anyone running aftermarket intake parts on a 305. Until someone on here posts results of aftermarket intake parts on a 305, my theory about stock TPI not hurting a 305 until low 13s may be a bunch of crap. If I could afford even used aftermarket stuff I would try it and post my results, but even used TPI stuff is way expensive. Anyone want to make any donations?

85rocker

Just throwing some stuff out...

My SLP runners showed 10 rwhp on a '91 LB9

A set of SLP headers showed 7.5 rwhp

A set of u-drive pullies showed 14rwhp

A set of 1.6 rockers showed 11 rwhp

Home Depot cold air showed 1/10 at the track

Headers=$500 + install fees
Runners=$300
Pullies=$75
Rockers=$250
Home Depot cold air=$19


I get a chuckle outta the u-drives on our serpentines. $75 gets me twice what $500 headers gets me. (Yes I know add a cam and heads and the headers start to pay off... but until you do they are a poor return on investment). Add another $25 for the shorter belt say $100 for the u-drive.

DuronClocker

iTrader: (1)

Displacement doesn't require air. Horsepower requires air.

While a 305 requires 13% less air than a 350, that means it is going to make 13% less power than a 350 with otherwise similar setups. If you are making enough power to get a 305 into the low 13s as a 350 in the 13s, they both need the same amount of air, so the TPI intake will become a restriction at the same power levels anyways.

A 305 can spin higher on a stock TPI setup than an otherwise similar 350 would be able to, but that doesn't mean it is making more power or going any faster.

smithtc

iTrader: (5)

Are you contradicting yourself?
Those mods and hp figures done in order?... You do realize there are 25 different scenarios of horsepower changes, don't you?
Not completely apples to apples, either. SLP headers not the best match, too expensive, and a 91LB9 has a better starting point than earlier models in regards to the exhaust system (2-1/4") w/ dual converters...if stock.

smithtc

iTrader: (5)

Then you're not looking.

85rocker

yah all over the map eh? I just wanted to show some results from a number of difference dyno pulls.

The point I wanted to make was the dyno will surprise you with what some mods will give (and some won't).

The SLP headers were the biggest and most expensive flop but then the '91 dual cat 3 inch cat back is already highly optimized. You can't expect headers to do all that much eh? Brand wouldn't make more than plus or minus 2-4 rwhp difference. Whoopee.

I never expected pulleis to show up so strong and after all that porting work on the runners what a disappointment. Lesson learned? Well this time I am bought AS&M LTRs. I'll post the dyno results on that next spring.

6SpeedTA95

I thought the dual converters were only on G92 option cars?

85rocker

in 91-92 they showed up in alot of unexpected places.

the option was called "N10".

87TPI350KID

Here it is: TPI was designed for the 305, thus it flow suffcient air into the smaller motor. The 305 does not need huge runners and base. SLP runners and bases were designed for the 'more hopped up' 350, which is starved for air by the TPI unit.

What im saying is, don't waste you money on parts that are way to big, same concept as using a 58 mm throttle body, not really needed. Do the mods that will make you engine rev faster, not higher, thus the result from the pullies.

As for only gaining 7 hp from the headers, thats fairly decent for a 305. It would have made more power if you went with some 1 5/8 instead of the again, too big 1 3/4.

85rocker

I was just reading another thread last week that outlined the birth of the TPI. The author made a strong and well articulated argument that the TPI was designed for a Corvette 350. Complete with historic references, etc. its somewhere here on 3rd gen.

You know I figured the same about the SLP headers and went to 1 5/8s instead and gained some low end losing abit of top end but not more than a few lbs tq and a few rwhp. It was equally depressing for all the coin I spent.

I have an L98 now so don't get much into the 305 battle. But if I did and what I have learned about the 305 is I would focus on exhaust, cam and spend as much as I could possibly afford on heads.

6SpeedTA95

Thats wierd I've read articles saying it was specifically designed to make a powerful 305 for the corvette because they wanted to drop the 350...they thankfully realized that was stupid

indirocz28

I got a question on Gasket Matching- Im swapping my 305 for a 358 zz4 with vortec's- now- i bought the vortec baseplate from edelbrock, and the high flow runners- I was thinking of gasket matching the plenum, but the baseplate should be fine the way it came right- since it is designed to add 10 - 14 hp?.. and the runners 18-20hp...so question is- i should be fine gasketmatching the plenum and leaving the baseplate the way it came ?

85rocker

If you want to get the most out of the setup you should gasket match the works.

ryane88

cam
heads
pulleys


exhuast
hi flow cat
headers
intake

TB
your runners

shift kit/flywheel
tranny rebo with better gearing (for topend or off the line w/e u want

gaskets

more air=more wear and higher temps
more fuel=well... thats heavy on ur wallet mainly

FIND that happy medium....

the 305 like a few have said isnt as air flow hungry anyway... so dont go huge on air...

roachjuice

long tube headers.... then if ya want 13's.... 3000 stall converter... then cam.... that is including intake and a few other cheap bolt ons....