When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
Hello thirdgen members, i have a question in regards to the stock tpi system. I plan on porting the tpi installed on my l98, but i was curious as to whether any manufacturers make a hopped up aftermarket tpi system. I was thinking about the holley stealth or a mini ram for a while, but i enjoy the low end torque the tpi offers, where these systems sacrifice the low end for high rpms. I understand its probably cheaper to port, but will require a lot of man hours. Any advice?
There are lots of people that have tons of experience and research on this subject that may interject more accurate advice but...
on a stock head, stock cam, the stock tpi IS limiting power however the gains aren't giant just yet. An hsr will give you results similar to a dual plane intake, the midrange 2500-3500 will see a loss, above 4500 or so you'll make 10-20 more hp. Some searching will yield direct examples. A mini ram will be a bit closer to a single plane result, *probably* less midrange but similar peak hp to the hsr.
A ported setup will net you gains though long runner stuff is currently carrying a premium with them out of production. The cost may outweigh the gains depending on your pocketbook or desire. The length of the runners will determine your rpm range, but the larger tubes will help your 350 breath better. More cam, more cylinder head and the gains really go up.
For your build, assuming you keep the long block, then you will want either a First TPI, or Super Ram with a ported base. If your intended peak power is below 6000rpm then with First (more torque) or Super-Ram (more HP) will give you a great street power band. Both intakes will really let a set of aftermarket heads shine down the road.
With the old L98 its a catch 22. The heads will jam up any better intakes like a SuperRam, or First TPI, not letting the intake breath to its potential. But the reverse is also true. If you drop Epic heads on a otherwise stock L98 sure, you'll gain power, but the intake and exhaust will choke the heads full potential.
This is why a planned and thought-out build is required on a budget. You have to know your end goal, so you an buy the parts in the best order.
For your build, assuming you keep the long block, then you will want either a First TPI, or Super Ram with a ported base. If your intended peak power is below 6000rpm then with First (more torque) or Super-Ram (more HP) will give you a great street power band. Both intakes will really let a set of aftermarket heads shine down the road.
With the old L98 its a catch 22. The heads will jam up any better intakes like a SuperRam, or First TPI, not letting the intake breath to its potential. But the reverse is also true. If you drop Epic heads on a otherwise stock L98 sure, you'll gain power, but the intake and exhaust will choke the heads full potential.
This is why a planned and thought-out build is required on a budget. You have to know your end goal, so you an buy the parts in the best order.
the end goal for this car is a road course build, i live in an area with lots of short, twisty roads that are very fun to drive with the tpi’s low end torque. I currently have been beefing up the suspension with a qa1 stage 2 handling platform, next up is kyb shocks and bmr springs, this car will probably never see a competition (i want to build a base model for that later down the road) but i’d like to have it set up to be able to run these twisties as if i were in competition. I bought an aluminum quad core radiator but it ended up not fitting my tranny lines so im back on the market for better cooling, i was thinking a mishimoto tri core with the upgraded dual electric fans packaged setup it comes with. Oh, and my other question was whether the runners can be ported? I heard somewhere that some machine shops will blast some kind of abrasive mud through them to widen the tube?
Factory runners can't be opened up very far. There's no material there. I don't recall seeing any results from extrude honed factory runners but I have seen it on bases. A first or a superram would probably be the best candidates for your setup. You do have to change a few things for a first but they are in production and available. A superram is a bit complicated for assembly which isn't as big a deal as the premium they're fetching as they aren't in production. Personally, I'd be looking into a first.
Based on your goals, I think your best bet, if you’re not going to invest in a set of aftermarket heads would be just run the stock runners and port your stock base – but only if you do it yourself. It costs too much to pay someone to do one right.
I had posted this before and did a bit of a cut and paste since it looks like most of it might apply to you.
Modify the top gaskets (as below) and trace them out on the stock plenum and the top of the stock runners (as below). Cut out the plenum’s dividers and port/shape as below. Bevel the runner FLANGE as below. Lay the edges back as far as possible but ONLY the area of the thicker flange material/area – NOT into the runners – the stock runners are too thin to “port”.
Leave the bottom flange of the runners alone - do not bevel or “port”. However, use a 1.5” sanding drum with assorted grit (leave about 0. 5-inch of the sanding disk hanging off the end) to take out the minor ridge at the top and the bottom of the runner.
TPI Base – at a minimum take out the lip or “bump” that’s right past the runner’s entrance/input of the base (see below), put a small bevel at the entrance, and smooth out the rough casting if you’re not going to port the entire intake. If you’re going to spend the time to do actual porting, you need a decent bit with a 6” shank to be able to port the entire length of the intake runner.
It takes some time to port a base and it’s really not worth paying anyone to do it right. If you’re not going to do the work yourself, get a FIRST if you want to stay with a long runner intake. It might seem expensive, but if you add up the costs of a replacement aftermarket TPI base (if you can find one), runners, and larger throttle body (like the FIRST has) it’s actually a pretty good deal considering the flow increase over even a ported aftermarket replacement base.
Other things that will help:
Add an adjustable fuel pressure regulator – set pressure to 40lbs as a start. Check plugs (immediately after a WOT blast – preferably 1/8 mile or so). Adjust pressure up or down as needed.
Adjust the lifter preload on the stock cam – set at 1/4 turn past “0”. If you’re not going to invest in a cam.
Set base timing to 10-degrees and run premium fuel (something equivalent to US 92-93 Octane)
Do all this and see what it does for you. None of this really costs a lot of money and won’t need any reprogramming (no chip needed). It won't make a ton of power but you’ll definitely notice a seat of the pants increase and might be enough of an increase for you if you’re not going to race it.
Next thing would be full exhaust. If you could do 1.625” long tube headers with a custom built 2.5” crossover and no catalytic converter into a single 3.5” pipe and muffler, that would give you room to grow if upping the power later. If never doing a larger engine, just put on a set of 1.625” shorty headers and change the muffler - the Ultra Flo Dynomax is the best stock replacement in my humble opinion. https://www.jegs.com/i/Dynomax/289/17577/10002/-1
Based on your goals, I think your best bet, if you’re not going to invest in a set of aftermarket heads would be just run the stock runners and port your stock base – but only if you do it yourself. It costs too much to pay someone to do one right.
I had posted this before and did a bit of a cut and paste since it looks like most of it might apply to you.
Modify the top gaskets (as below) and trace them out on the stock plenum and the top of the stock runners (as below). Cut out the plenum’s dividers and port/shape as below. Bevel the runner FLANGE as below. Lay the edges back as far as possible but ONLY the area of the thicker flange material/area – NOT into the runners – the stock runners are too thin to “port”.
Leave the bottom flange of the runners alone - do not bevel or “port”. However, use a 1.5” sanding drum with assorted grit (leave about 0. 5-inch of the sanding disk hanging off the end) to take out the minor ridge at the top and the bottom of the runner.
TPI Base – at a minimum take out the lip or “bump” that’s right past the runner’s entrance/input of the base (see below), put a small bevel at the entrance, and smooth out the rough casting if you’re not going to port the entire intake. If you’re going to spend the time to do actual porting, you need a decent bit with a 6” shank to be able to port the entire length of the intake runner.
It takes some time to port a base and it’s really not worth paying anyone to do it right. If you’re not going to do the work yourself, get a FIRST if you want to stay with a long runner intake. It might seem expensive, but if you add up the costs of a replacement aftermarket TPI base (if you can find one), runners, and larger throttle body (like the FIRST has) it’s actually a pretty good deal considering the flow increase over even a ported aftermarket replacement base.
Other things that will help:
Add an adjustable fuel pressure regulator – set pressure to 40lbs as a start. Check plugs (immediately after a WOT blast – preferably 1/8 mile or so). Adjust pressure up or down as needed.
Adjust the lifter preload on the stock cam – set at 1/4 turn past “0”. If you’re not going to invest in a cam.
Set base timing to 10-degrees and run premium fuel (something equivalent to US 92-93 Octane)
Do all this and see what it does for you. None of this really costs a lot of money and won’t need any reprogramming (no chip needed). It won't make a ton of power but you’ll definitely notice a seat of the pants increase and might be enough of an increase for you if you’re not going to race it.
Next thing would be full exhaust. If you could do 1.625” long tube headers with a custom built 2.5” crossover and no catalytic converter into a single 3.5” pipe and muffler, that would give you room to grow if upping the power later. If never doing a larger engine, just put on a set of 1.625” shorty headers and change the muffler - the Ultra Flo Dynomax is the best stock replacement in my humble opinion. https://www.jegs.com/i/Dynomax/289/17577/10002/-1
HTH
i’m not quite sure yet how to quote parts so i’m gonna just quote the entire thing lol. As far as heads go, i would like to eventually get a set of aluminum corvette heads for the tpi and port those as i’ve heard theyre much better than the cast iron heads i have. Plans for the motor are i want to stroke it out to a 392 as i’ve heard any larger than that and i’m pushing my luck, cam/lifters/valves will most likely be done at the same time as that. I went and picked up the new plenum to port today, and the guy i got it from had a ridiculous one of a kind tpi system built by one of his buddies, this thing was nuts man. Professional. It was wider, had 2” runners, but retained the stock look. I’ll take a screenshot of the video i took and post it here, see if anyone can’t dig up something similar. But pther than that plan is i figure once i’m able to stroke the motor i’ll probably be well off financially enough to go positive dispo SC and wont even worry about going nuts with a tpi, i’m just trying to open her up enough to bully the local weedeaters here and there. Problem about my exhaust is the previous owner welded a new cat in himself, but i have a nice 2.75” exhaust already installed and guy has a 2.5” in/out cat rigged on it. Dude must’ve been a magician with a welder, after i port out the tpi/base/runners like you described (much appreciated help btw) i’m gonna cut that monstrosity out and install a high flow cat, maybe get some long tubes and just x pipe it with my tax return or something. The bones of the build plan arenin place, i’ve just been winging the finer details for now as i’m not in the wealthy percentage of the population
As someone who's done it, I'll never touch another TPI intake. Use? Sure...but it'll be stock. Just sooo....much...work, for too little gain in my opinion. You mention fun on the twisties. A 5 speed swap will gain you more fun than any motor you could ever put in there in my opinion, so until you get rid of that automatic, there's no point looking at the engine. And if you DO keep the auto, get a bigger stall. I ran a 2400 stall B&M for a few years and it was night and day more fun that the stock auto stall.
...another thing to keep in mind when looking at power curves and losing torque, etc. etc., is that we talk on these forums like it's all or nothing. Like TPI is the only game for torque. ALL the other intakes make just as much torque. They just make it a little higher up in the RPM band. So you have a rev a second longer to get into your power band. Is that gonna limit your fun? No, it won't. Don't overthink the torque curve on a mild build. Anything that'll help you make more power will be a benefit, OR....at least, not hurt you. It's important to understand all the concepts, and as others have said, pick proper components that will be part of a well thought out system, but don't get caught up in forum numbers and theoretical concepts. TPIS used to say how their TPI intake made 90 more hp than a stock TPI on a mild L98. And it did. (and I'm spitballing the numbers here) but it was like at 5800 RPMs. At 5000 RPMs is made about 15 more, and at 2800 RPMs is made like 15 less. Those numbers didn't make it into their magazine add though, imagine that.
I had a 5 speed with a 3.27 gear, full exhaust and suspension, and a stock L98/TPI with a zz4 cam and the car was an absolute blast to drive. I ultimately went with fully ported aftermarket TPI stuff, Holley EFI, RHS heads on a 383, TKO 5 speed, and sure, it was faster, but no way was is even close to being worth the work imho. That zz4 cammed L98 at least to me, was every bit as fun, especially for the effort.
Hey guys, i ended up finding a pretty sweet used setup for a good price. Edelbrock hi flow ported base i’m gonna pick up next friday, edebrock ported plenum, bbk 52mm TB. I’m gonna get the tb and plenum tomorrow and just run those until i can pick up the base, which will come in at perfect timing as i personally believe i botched the intake gasket install last time i had it all apart so i can do it right this time. I’ll just run this setup until i can get some aluminum corvette tpi heads i’ll port and polish, which will also be perfect as i’ve got bad valve guides. This car has been setting itself up to get little (but important) parts fixed while i’m doing a big job pretty much since i’ve owned it. I swear the damn thing has a personality and mind of its own, like its sayin “oh hey while youre in there i need this too real quick” 😂😂
As for the intake gasket, theres nothing largely obvious that says i did it wrong, car runs and idles smooth as ever, its just little things here and there that are synonymous. A smidge of bogging in the upper rpms before it powers through the rest, occasional rough idke at start for a couple seconds with slight but telltale sucking air noise, not often at all but its there
Hey guys, i ended up finding a pretty sweet used setup for a good price. Edelbrock hi flow ported base i’m gonna pick up next friday, edebrock ported plenum, bbk 52mm TB. I’m gonna get the tb and plenum tomorrow and just run those until i can pick up the base, which will come in at perfect timing as i personally believe i botched the intake gasket install last time i had it all apart so i can do it right this time. I’ll just run this setup until i can get some aluminum corvette tpi heads i’ll port and polish, which will also be perfect as i’ve got bad valve guides. This car has been setting itself up to get little (but important) parts fixed while i’m doing a big job pretty much since i’ve owned it. I swear the damn thing has a personality and mind of its own, like its sayin “oh hey while youre in there i need this too real quick” 😂😂
IMHO I think you should put large tube runners with this. Your stock runners become the "choke" point of the system, but I do understand those runners are pricey in these times.
IMHO I think you should put large tube runners with this. Your stock runners become the "choke" point of the system, but I do understand those runners are pricey in these times.
i do plan on getting either slp’s or edelbrocks once either they become more affordable or i get enough cash in my pocket, but the stock ones will have to do for now + a little porting. In the meantime, i’ve picked up a 3.42 posi from a 95 z28 and and gonna be getting 28 spline axles from a 91 z28 to fit, i just picked up a set of used hedman shorties yesterday and started cleaning them up earlier. Should be ready to get put in by monday. The whole parts pull so far is the posi rear diff, 28 spline axles, ported plenum, hedman shorties, and i can’t decide between a TPIS big mouth, edelbrock hi flow, or accell ported base. The guy i got the diff from has all 3 bases. When i do the install of all mentioned parts i will also be gutting the air box of the plastic bottom as its stupid how restrictive it is, as well as removing MAF screens. After this all i’ll have left to do is shocks, springs, and tires and i’ll be happy with it for a while, while i try to pull a rabbit out of my *** in getting my bimmer to pass smog
