Hey guys. I thought I would share pics of my plenum, for the heck of it. Or maybe I'm just way too excited to have done this to my plenum. It was definitely fun!

Today I finally siamesed my stock plenum ports and "radiused" the ports for the throttle body. I guess it is supposed to improve throttle response and give the tpi cars a bit more power at higher rpm. I haven't tested it out yet because I don't have a steering wheel.

Check out the pics below. I also polished the plenum, up to a 600 grit sandpaper just to make it shine a bit more.

Below, you can see where I cut out those "walls" that are between the plenum ports. You can also see where I cut out those bottom walls that were once just inside the throttle body ports.


Below, you can see a better view of the throttle body ports. I didn't make them perfectly round on the outer sides, but I rounded them off pretty good and totally did away with the walls at the bottom of the ports.

 

I like this picture:



And another:

 

Not bad at all.

 

Thanks. I hope I notice some difference past 2000 rpms or something.

 

looks good. Is it possible you could radius the triangular area where you took out the dividing wall between the runners? it seems to me that would help it flow much better

 

Are you planning on running stock runners with that setup....?

 

Yes.

I just wanted to open up the airflow in the plenum to give the stock runners quicker, smoother air.

I won't gain rpms but will get a better throttle response and a few more ponies up top, is my guess.

 

Sure it's possible to do that with more time invested. I figured that by getting rid of the major portion of those walls that the air will find its way quickly enough, whether I get rid of the remainder (upper and lower remaining portions) of those walls or not. What I removed was a pretty good chunk, between each port:



I figured there would be plenty of air finding the path of least resistance, basically, and that the air would move a bit more quickly through the openings I created. Who knows for sure, but I think it will help me when over 2000 rpms, up to redline, especially after I do a valve job and put a new camshaft in the engine.

 

i did a some porting to my plenum,i used a carbide bit and it kept clogging with aluminum.what did you use ?

 

I'll be happy to gain 50 horses, from a cam swap, fuel pressure regulator, remote coil, and a little headwork on those 416's, which are decent heads, as far as GM factory heads are concerned.

I'm also going to open up my snorkel air intake a bit more, too, underneath where the filters rest. I'm not sure how much that stock design restricts airflow, but it looks like it could be a restriction.

I don't want to go crazy with the 305 because my budget sucks. I just want to wake her up a bit. I think my plan is sound. When I get a tru trac posi and install those 3.42's and tighten up the rear with a new panhard rod and control arms, she'll be a nice street car.

 

I bought a plenum that was machined simmilarly to what you have. What you did looks good and should produce a few more HP.

 

I used a carbide bit, too, that looked like a little gear sort of, and a 10000 max rpm dremel. I used cutting oil and only had to pick aluminum out of my bit twice (on about half the teeth).

I cut lines on the port dividers with a cutting disc then cut them out with a mini hack saw. It worked great.

 

Thanks, I hope so.

 

I finished up and cut the gaskets to match last night, and I put the plenum back on my engine. I started it up but couldn't drive anywhere because I lack a steering wheel.

The frickin' car sounds mean with the Hedman shorties, Hedman 3" y pipe, and 3" exhaust all the way back, with a Powerstick chambered muffler (3" flowpath) in the middle. I love how it sounds. Guys with LT1's and LS1's hear it and are always afraid to run me (even though they'd waste me). Wish I could take her for a drive up an onramp and see if I can tell a difference.

 

thats why,i didnt use any oil,and used a carbide burr bit.i wanted to do more but i got pissed with cleaning the bit.

i only ground down the ramps at the t-body opening and that seems to have helped it.

anyone think there would be a benefit to removing the divider behind the throttle body?

 

Yeah, make sure to use cutting oil. It does help quite a bit.

I wouldn't mess with the divider by the throttle body ports. The throttle body itself will serve as the divider anyway, no matter what you do to the plenum in that area. I'd leave it be. I can't see a benefit from doing that.

 

I decided I'm going with a Lunati Barebones cam kit. $89 for a cam and lifters can't be beat.

Advertised Duration (Intake/Exhaust) 270/280
Duration @.050" (Intake/Exhaust) 204/214
Gross Valve Lift (Intake/Exhaust) .420"/.443"
Lobe Seperation 112
Intake Center Line 107
RPM Range 1000-5000
Cam and lifters included in kit

It'll be better than the stocker peanut cam, that's for sure.

 

You're getting there, you need to smooth the entry to your runners, and you can open them up (the cast flanges are a bit smaller than the tubes, open them till it's all smooth). The real power is in the base, that's where you need to smooth, reshape, and generally hog out some metal. I have some pics of my work on the stock setup just search my user name.

 

I plan to do some more work on the runners and on the base, when I pull the top off, for my cam swap.

Thanks for the advice. Much appreciated.

 

Well the little 305 seems to breathe better now, but I seemed to have lost some torque with the upper plenum mod.

I definitely need a better camshaft now. The stock cam in the 86 LB9 really sucks.

I'll post before and after pics of the base, too, as soon as I get it done. I might as well do it.

I've heard it's not a bad idea to siamese the stock runners in about 1/4", too. Is this true?

 

You mean shave off that ridge that's just inside the entry to the runners?

I'm trying to visualize what you are saying.

 

Heck with it. I'm doing an LT1 swap.

 

that cam you posted is just a little better than a stock 88 l98 cam...i would go with the crane 104224 cam which is 214/220 452/465 112 lsa... and best of all no head mod required..its designed for tpi motors... lt1 cam is better than your peanut cam but its still only slightly better than a stock l98 cam.... your still leaving alot on the table as far as cam goes..... the plenum is nice but all your work will go down the drain with those stock runners.... why do the plenum if its going to be a restriction because of the runners..... i would keep your stock base and maybe just port it lightly because it was designed for the 305... but i would get slp runners for sure.....

 

i'm sorry but the physicist in me says you need to radius those ports. the triangular area with the corners cannot be good for flow. the ports should look more like a peanut and the old dividers should be radiused to promote freer flow. those sharp corners are just going to create low pressure areas and turbulence. neither of which will help power and could even hurt it

 

I would LOVE to see stock ported entry and exit runners vs high flow runners on a stock base. I don't think you would see much gain. People say the runners are the restriction, but I believe that the main restriction is in the base.

 

so.......... im running a complete stock L31 (2000 vortec 350) with the edelbrock hi-flow tpi base with stock runners,plenum and throttle body.would i be wasting money on slp or edelbrock runners?

 

I hear a lot of guys say that they don't think the slp or edelbrock runners are worth it.

 

I'm doing an LT1 swap. Heck with it.

 

Rock on!

 

i hate carbide bits :P lol..had to wear a full mask to use one.anyway..
looks good..

 

You should try siamesing the base before you go LT1. There's a lot of work involved in that swap, more than I think it would be worth on a 305 car. If you siamese it and don't like the results you can always look at different options.

 

Yeah! First thing I'll do, once I get it running, is swap to LT4 heads and intake, and run a mean cam, and, of course, computer tweaking.

Should give me around 450 hp.

Much better than 200 hp.

 

Really? I'm surprised. It seems the later generation small block engines are more efficient and can make more power.

It seems it would be a worthwhile swap....worth the effort.

 

Ah, you thought I meant just an LT1 INTAKE swap. I'm talking about doing an entire LT1 engine swap. Now I see what you meant. Yes, trying to fit an LT1 intake onto my 305 would be a horrible job, and it would not be worthwhile.

 

make sure you get a new or aftermarket opti-spark. that thing is prone to tons of problems

on a side note did you ever sell your plenum?

 

Also at this point I see absolutely ZERO point in swapping an LT1 into a car, LS1's can be had for close to the same price and the potential is phenomenal. Do you already have the LT1? Or did you just figure it would be a good swap?

N/M I answered my own question! 1800 for a full donor car, you're SET! That should be a strong running setup when you get it all squared away ")

 

I didn't have the plenum up for sale. I just posted pics of it. I'm selling my entire 305 tpi engine and tranny, though.

 

I read your post and initially was thinking, "What, why?" Then I saw you answer your own question.

I was just about to post and direct you to another of my posts that discusses what I am paying for the 97 Camaro. The only thing it's missing is the steering column.

I agree....$1800 for the donor car that has the complete engine/tranny/ecm/harness, etc. will allow me to part out the 97 and do my swap, with minimal or zero out of pocket expense.

LS1's are the shiznit, but, for me, free or cheap horsepower wins every time, and and LT1 will just have to work for me, at this point.

LT1's are pretty darn good engines and have great potential.

To upgrade from my 305, at virtually no cost to me, makes a lot of sense, to me, AND it's better than an L98 swap, in my opinion.

It will be way worth it.

 

I thought this looked like a nice upgrade.

http://www.dynaspark.net/advantage/

 

Did the same to my plenum, only I took the walls insde between runner ports out as much as i could on the top/bottom. From what I understand the TPI plenum size is too small for a 350 or larger since it was designed for a 305. Same as adding a spacer between carb/intake or TB/plenum helps some hurts others. tho i do agree on grinding the egr bosses helping flow more.

Still I'd buy a stealth ram if i had the extra moola

 

The plenum for the 305 is the same as the one for the 350. I'm saying heck with it and doing a complete LT1 swap.

 

cool!
i think what he was saying is that plenum size is supposed to be related to engine displacement. when you bump displacement by 45 ci, you have to bump the plenum size as well... gm didnt

 

Actually, I like the idea of the LTCC on the LT1, over just an aftermarket optispark (the Dynaspark looks way better than the MSD). LTCC is a bit more challenging to install and will most likely end up being more expensive by a few hundred bucks, since the later generation coils are used, but it should kick ****. I Like the idea of not needing the rotor on the distributor in the LT1. These are pretty common failures in the optispark, from what I've read--but some prove pretty reliable.

The LTCC just looks superior to the Optispark, in my opinion.

http://www.delteq.com/products.htm

 

I think the plenum works better on a 350 than on a 305--it seems to prefer a bit more displacement than 305 c.i. It probably has more to do with the runners than anything else, as far as breathing.

It seems that the runner length is "overcome" by larger displacement, to a point. The plenum is plenty big, in my opinion.

 

Yah thats what i was saying. But even taking those walls out and grindin down egr boss only increases it like a few % about the same or less than a spacer. I read a few places the ideal plenum size is somthing like 50-60% of displacment and some1 on here said tpi was like 45% so 5ish% a few % more for a 350 maybe. Also knowing that GM built it around the 305 runner sizes too(not talking lenghts) and I know the stealth ram has a larger pelnum volume.

I'm just saying you wouldn't put a victor JR on a 305, you'd kill the bottom end. Still I bet some1 has made a 305 rad enuff for one. Plus I don't know his mods, but my point is the 305 should be breathing good a egr boss port better, but increasing the plenum % too much and it's just like putting too big an intake on it. Relooking at the pics and my plenum he took out about 1/3 more than me. I thought the bolt humps were the lower part of the walls. So I'm betting w/o heavy mods this would do more harm than good on a 305.

https://www.thirdgen.org/forums/tpi/...powerband.html