skunkIROC

let me start by pointing out that all this is still in the planning phase. i just want to narrow down some options/issues before i jump into this with bad ideas.

that being said, i have an 88iroc with an L98.

for suspension it has poly bushings in the front control arms, moog springs all around, kyb gr2 shocks all around, spohn 36mm front control bar, BMR rear control arms and panhard bar, and spohn sub frames welded in.

engine has k&n intake, headers and thats it. i want build the engine since i have a chasis and suspension to handle it. the guy who helps me do most work to my vehicles said he could build me a pretty mean 383 for about $3500. this brings me to my question REGARDING TPI, FINALLY! can i stick with the tpi, or should i put a holley 750 (or something similar) on it? i understand that the tpi falls on its face earlier than other intakes, but i'm already stretching my funds by stroking the engine, so going out and buying a stealth ram probably isnt in my immediate future. HOWEVER, i dont want to spend money on an engine and essentially WASTE it by keeping an intake on it thats not up to the job.

opinions, please. like i said, i dont want to jump into this with bad ideas-

ZONES89RS

iTrader: (2)

I have a 383 in my 89 RS, I could never get TBI to function in a million years, you are on the right track $$$ wise on the intake, you have the option of going carb and then upgrading later, that is my suggestion, I would go for TPI economy wise if I had the money, but I am a budget builder and I get ok mileage with a 5 speed and a carburater, I eliminated the choke so cold startups arent fun but I dont care about those 45 second drivability issues when i first crank it up, if you drive it daily and dont want issues, spend the extra cach whitch will be allot more, but if you are young and dont care you know the option.

xpndbl3

iTrader: (5)

sell tpi and use those funds to purchase everything to swap over to a 750 double pumper holley and a air-gap style dual plane intake.

ZONES89RS

iTrader: (2)

Great minds thing alike.

skunkIROC

how much would i be looking at for the 750 double pumper and intake you speak of?

1bad91Z

iTrader: (1)

Save your money and build a 355. The money you save by not building a stroker, you can upgrade your TPI or buy a Stealth-Ram etc... and still have some $$ left over.

Example:

Buy a running (decent condition vortec 350 pull-out motor from a salvage yard). Have your machinist turn the crank, re-size the rods, bore block .030 over, and throw in a nice set of pistons, rings, and bearings. Then swap in a decent cam. You have just saved all the money from not buying a stroker crank/rods and a set of heads. The Vortec heads make decent power even stock. Now you have money for intake upgrades etc......

Just a thought.....

Grim Reaper

If you plan to modify the engine, I would stick with EFI but not a stock TPI/long tube runner system. I would switch a different intake like the Holley Stealth Ram.

wizzard2076

tpi is great although you will need to use a mass air system they work better than speed dencity. for modified 383s thats what i ordered and plan to use for my own 87iroc roots supercharged 383 5spd 100hp shot nos just in case. good luck.

Oh yea carbs suck unless you just like hard to start cars that are not as quick with throttle responce. and adjusting them all the time.

ZONES89RS

iTrader: (2)

Carbs are not for all, as I directed above, I only adjust the carb for nitrous use, its fine besides that.

turbotater

I don't know how many of these people answering have built
this combo but some of the answers are not accurate .
my 383 with a gm torque converter-stock gears-stock throttle body
modified runners-vortec heads-small cam has run 12.8's @ 105 mph
gets 22-23 mpg on the highway and is dead reliable all year round and
its a speed density car . you need to decide on some performance goals
and then buy parts not buy parts and see what happens.

mike

1991CamaroRslow

iTrader: (3)

I vote for keeping your TPI or swapping to a Vortec headed, stealth rammed 355. You'll get more speed out of the Stealth Ram 355 than you will out of the 383 TPI combo but that combo would be quite fun to cruise. From the sound of it you have a more handling/driving oriented car, either combination should be quite fun to drive. What're your goals for the car?

Grim Reaper

That's an opinion. There are advantages and disadvantages to both. I've tuned both and frankly BOTH can benefit from a good tune - even on a stock engine.

SD is cheaper to implement as the MAP sensor is readily available at wrecking yards and they very rarely fail. Also, the ECM for SD is readily available and cheaper than the ECM for MAF.

I don't advocate throwing away a perfectly good working MAF system, but if your MAF dies or you need a new ECM and you can't locate a used one, converting to SD can be a cost effective solution.

Grim Reaper

Of course, the ultimate power will depend on the cam selected. Since a stock TPI system runs out of breath at low rpms, there is little benefit to going to a larger cam to make power. While the HSR 355 you can run a larger cam and will sacrifice some bottom end torque but the top end will more than compensate. But the HSR still promotes a fair amount of low end TQ.

I personally like the torque curves of the HSR. With a 383 TPI car, you may find launching an issue and need to do some work to ensure proper traction. An HSR will make it easier to launch while having a nice top end as well.

skunkIROC

i'm probably not going to use the car as an 'all-out-racer', and do intend to drive it to work often. i have a harley to use as back up if something should happen to go wrong with the car, so its not my ONLY source of transport down here. i DO want a nasty sounding cam in it though, one that at idle sounds very distinct. there was/is a member named EVILCARTMAN who had a sound clip of his 383, and that particular sound has had me hooked on building a nasty 383 for years now.

this may sound kinda sick, but i'm less worried about making the power as i am having that sound. i'd rather have a good-running(reliable)/good-sounding car with nasty cam than a okay-running(not always reliable)/very-powerful car. i dont know if that makes sense or not? but maybe that clears up my goals for you guys?

1991CamaroRslow

iTrader: (3)

Keep the TPI, port the base and plenum, get a cam such as the ZZ4 cam, run long tube headers with duals and classic chambered mufflers. This would get you a killer sounding car with enough power to most likely satisfy your need. The kicker is it would be cheap.

skunkIROC

did you mean just do those steps listed, OR do those with the 383? also, isnt it almost impossible to do true duals on our cars

1991CamaroRslow

iTrader: (3)

Do those with the 383. You can run duals on our cars, you sacrifice some ground clearance but if it's the sound you're after nothing beats the dual pipes. Check out the exhaust forum several guys have ran true duals including me.

skunkIROC

now as far as ehaust, i have shortys already. so would i really need long tubes? also, when you say classic chambered, do you mean flowmaster 40's?

would porting the base and plenum be as simple as taking them to the shop and saying "port these"?

1991CamaroRslow

iTrader: (3)

Classic Chambereds are NOT Flowmasters at all, they look like glasspacks but have pinches in them. They're the mufflers that were popular in the 60's and 70's. http://www.classicchambered.com/ carries them, the owner is a member of TGO. You should be able to make due with the shorties. As for porting the base, for me it was as simple as buying a die grinder and carbide cutter bits then going to work. I'm sure if you have a shop that'll port intakes and such you can get it done there. I myself liked the savings and satisfaction of doing it myself. The ZZ4 cam can be had for cheap because it's a GM part that they put in crate engines. It has a short duration that works well with the TPI and decent lift numbers. There are probably better choices but I think it will give you what you want for cheap. I'm surprised no one else has chimed in on this one. Give it time I'm sure some other opinions will come along.

Abubaca

iTrader: (3)

Carbs suck? TPI with a roots blower? SD is better than MAF? Ummmmm, ok.



Not a bad idea at all!

VERY true. Not that a 383 TPI is bad, or can't be fast, but they require more of a overall matched car. Suspension and gearing to accomodate for the low end torque. A taller gear to help with the lower top end. A cam that flows enough for the displacement, but still won't outspin the TPI. By default of having all those cubes, they make power, and they're cool, but not really an "ideal" set-up.

Nah, I understand that. A big ole sick cam would be wasted with a TPI, regardless of sound. OK, this is a VERY BROAD GENERALIZATION, but "typically", that awesome lopey sound comes from a cam designed to run at higher RPMs, the TPI makes power down low. Not saying you can't do it, but it's not really ideal. ....and you don't need cubic inches for that sound. The right cam in a V6 will sound INSANE!!!!! ...ask RedRaif.

....not a fan of long tubes with the TPI. Like every example so far, it's not that you can't, but it doesn't mean it's absolutely the best choice. A ZZ4 cam and a TPI don't need long tubes. They just don't flow enough. If ya had 'em already that'd be different, but since you have shorties, that's your best bet IMO. ....and this is just an opinion, but I HATE the sound of chambered mufflers with anything but the biggest nastiest cam out there. They NEEEEED to lope to sound good IMO. Again, just an opinion.

Some shops will, some won't. Your best bet I think would be to do a few searches, read up and learn, and try to do it yourself!

I'm running a ZZ4 cam (and LT4 valvesprings), SLP 1.75 shorty headers with an otherwise stock L98, a 2400 stall and a 3.27. This is an awesome combo for the money/effort. The ZZ4 cam runs GREAT, and that's on a stock tune still. I've heard rumors ZZ4 cam was the original cam ground for the L98's on the vettes, but was sidelined for emissions reasons. I dunno, just a rumor, but the point is it's a great mod. Bought mine for $60 bucks. Again, maybe not ideal for a TPI/383, but a great cam none the less.

Sound to me like you should concentrate on some "decent" heads, a different intake (maybe the HSR) and a cam. You'll still make some killer power, you'll get a killer sound, and you save the money you woulda spent on the 383.

Is the L98 you have running well? You may be able to use it as is with NO work. Slap a set of Vortechs heads on it ($700ish) with a vortech/HSR, ($750ish) a cam ($300ish) and you've still spent less than $2000. That leaves $1600 for bolts, hardware, lube, wires, plugs, oil, blah blah blah.

skunkIROC

first off, thanx to all who replied (especially abubaca), i dont want to stray too far from the TPI topic, so hopefully i've gathered the info nessecary to concoct the combination i wish to "make good noises with"

i spoke with evilcartman, he explained that he doesnt have a 383 like i thought. he was running shorties into a spintech (intsead of a cat), followed by two more feet of 3 inch pipe to make that sound.

this brings me to my "possible" conclusion =
1.install HSR, cam, and heads.
2.run a similar exhaust setup off of my shorties.
3.then post a sound clip for all to see how i've acheived the sound i thirsted for? yes?

Abubaca

iTrader: (3)

Happy to help.

You mentioned that EvilCartman had a Spintech? Those are GREAT sounding mufflers!

....and just so you weren't confused, as much as I love my zz4 cam, it's NOT the cam if ya want that awesome sound. There's no doubt that it's not stock, but it's not what I would consider a big cam by any means. I think it's a great TPI cam, that's why I mentioned it.

Brisk

iTrader: (25)

you could always try a LT4 Hotcam.. I believe its a good choice for a L98. Check my video for a sound clip. CLICK HERE

Check my VB Garage for mods.

Abubaca

iTrader: (3)

Holy crap, that sounds awesome! ...proof that big cubes aren't needed.

Brisk

iTrader: (25)

thanks Abubaca.. all that out of a lil' 305

dave-92gta

iTrader: (1)

do you know the specs on that cam? what kind of specs are on your car to make it sound like that? carb? exhaust etc

Abubaca

iTrader: (3)

Cam:---------Duration @ .050--------------Lift:-----------------LSA

L-98------------ 207 - 213--------------.415 / .430--------------117
ZZ-4------------ 208 - 221-------------- .474 / .510-------------112
LT-4 Hotcam------218 - 228--------------.525 / .525 (w1.6)-------112

The biggest factor in "sound" when talking cams is overlap. The higher the duration, the longer the valves are open, and the overlap area where both valves are open causes that lopey sound. Ideally, you don't want overlap for performance reasons of course, but at higher RPMs, the additional air received from the longer duration is necessary. It's a trade off. The car has less driveability, but higher performance. The smaller the LSA, the more overlap as well, and again, it's a low end lope trade off for higher RPM performance. Carb, EFI, it really doesn't matter. My ZZ4 cam has a mild lope to it, and driveability hasn't suffered at all that I can notice. I'd imagine that driveability with the LT4-HC is good too, although it's obviously a bit more choppy. You should still have PLENTY of vaccum for brakes, right Brisk?

dave-92gta

iTrader: (1)

oh to add that. i have not chosen a cam yet, but i wanted something around .530 ish intake and .550 exhaust. the heads have can take up to a .600 i think.... have to look into that, just like Abubaca asked about vaccum for breaks breaks...what about vaccum for cruse controle? i want to keep mine and if i cant have enough vaccum, i will get a vaccum booster or maker. i have not looked into that route but i have herd a few thigns about it. if someone could clear that up for me that would awsome

88BlackZ-51

iTrader: (2)

Ditch the "TPI". It sucks!

Yeah I know, but this guy made this amount of RWHP. Blah! Blah! Blah!

The majority of guys with the long runners make tons of low end, and nothing on the big end.

BadSS

If you know how and when to apply the TPI systems, they're great. If you don't,,, they'll "suck". Most street engines are built "middle of the road",, meaning that it's not going to make a lot of difference what runner length you put on the car,,, it will run about the same ETs - assuming proper car and engine combination choices (which most don't get right for the long runners) and traction. About all you end up changing is the powerband and shift points. Personally,, I have no problem shifting at whatever RPM the car whats and I actually prefer not to spin the engine any higher than I have to run the ETs I'm looking for. Main thing with the long runner systems,, even the off combination ones,,,, you have to have a good suspension and tires and know how to drive to get the ETs out of them. If you're not willing to spend the money to hook or don't want to spend the time behind the wheel perfecting the launch procedures, go short runner. Most people will run better ETs with the short runner systems purely and simply because they are easier to hook and don't require much if any driving skill on mid twelve second car.

As far as the poster's real question,,, just as I typically would not inject a car with a carb,,, I wouldn't carb a car that was injected. Unless you're buying used and good dual plane intake will run $180, carb fuel pump $60, carb $400, dizzy $150,,, so you could do the StealthRam for that - assuming the fuel pump and current injectors would work for the power level you're building. The cross-sectional area on the stock based TPI systems are marginal for a 383. For the larger cubed engines,,, it's not so much the runner length "choking" the engine as it is the limited volume of air trying to pass through the small port area. Saying that, the StealthRam is a good choice, especially since most local racers build combinations that have worked well for them and their carbed cars. The power band on the StealthRam acts a lot like a dual plane carbed intake,,, and will match most "carbed" built combinations a whole lot better than even a serious long tube runner system like the FIRST Injections intake.

88BlackZ-51

iTrader: (2)

I was referring to the stock TPI. Yes it does "suck" royally. I hope you dont disagree with that statement.

doc

I would stick with the ECM and MAF, he has an '88, so it should be a MAF car.
The 383 is a great idea, tons of torque! Currently, I am running a ported SuperRam on the 395 stroker. But I'm thinking of switching to the StealthRam.

BTW: you will need to find someone to custom burn an Eprom chip for your 383.

Grim Reaper

And I bet everyone told Chris/Brisk that the Hot Cam was too big for a 305 and he was wasting his time on a 305 as well, except some "old boot" he met on the Internet.

I wish I had a sound file of my buddy's 383 MR/AFR with a solid roller 248/256 @ .050 .600 lift and a 110* LSA (but he wishes he had gone with the 106* LSA like I recommended). His is really lopey even with the whimpy 110* LSA.

His 383 has no problem with his vacuum for the brakes and he doesn't use a vacuum booster either. I just did a little tuning.

dave-92gta

iTrader: (1)

probably no cruse eh, i know most people ditch cruse when they go higher preformance but i want to know if i can still use it

Grim Reaper

I will have to confirm that with my buddy next time I speak to him. I do believe it is still functioning because he's never stated it's not working. However, he doesn't use that car as his "highway car".

1991CamaroRslow

iTrader: (3)

Something you need to keep in mind is that bigger cubic inches will tame down a bigger cam. If you're concerned about the sound I'de stay 355. If you're concerned about price I'de hand port your base/plenum and stick with the stock runners; I woulnd't recommend aftermarket runners due to the fact you can get a Stealth Ram for close to the same price. A REALLY good combo for you would be the 355 with your choice of intake, ZZ4 or LT4 Hot Cam (ZZ4 will provide more torque and match to the stock TPI better, HOT cam will give a higher torque peak) I believe the ZZ4 cam will have a little lumpier idle but I may be wrong. Finally get a good exhaust. My chambered mufflers make the car sound as if it's cammed, it's not. They also sound killer at WOT on and off spray. They sound WAY better than the old bullet I had in the cats place and better than the V Force (genero flowmaster) I had in the cats place.

WheelsUp84z

iTrader: (2)

went carb and wont look back, id rather turn a few screws than have to get a new chip burned everytime i changed things... a lot less things to go wrong, a lot easier to troubleshoot, but.... EFI is much more efficient, you'll get better gas milage (if you're even worried about that) and you can tune it more finely to squeeze everly last pony out of that motor. IF you stick with EFI, you need to switching to an aftermarket intake, you can sell the stock set up to put some money twards it.

rgarcia63

Almost a match for what I have in my MAF '88, but I haven't run the 1/4 yet. It get's better MPG than when it was a stock 350. It's a great stress reliever.

- RJG.

Grim Reaper

You are very correct on the first point. Basically a 383 will make a cam sound smaller than in a 355. It's not much, sort of like a 230/236 in a 355 would sound like a 224/230 (one step=6*) if installed in a 383.

On point two, a ZZ4 cam is really quite mild. It's over two steps smaller than the LT4 Hot Cam (excluding 1.6 rockers).

But I will say this, the cam must match the intake. A LT4 Hot Cam is probably the biggest I would run with a TPI, and might be one step too big as the TPI is running out of breath where the LT4 Hot Cam is really shining. But, if a different intake might be in the future (say a HSR), then go with the LT4 - as an Intake Swap will be simple after the cam change.

Comp Cams makes a couple of cams around 212/218 that would be a good compromise between the ZZ4 and LT4 Hot Cam. A 110* LSA would make it lumpy while making great mid range torque (compared to a 112* LSA) that would match the TPI setup better.

Abubaca

iTrader: (3)

....I agree totally. And you also made a good point about the hotcam. Without the 1.6 rockers, it's actually SMALLER than the ZZ4. Hehe, GM and they're shifty marketing!!! LOL

Here's a list I made a while back. Obviously there are unlimited cam choices, but when I first was trying to decide what I wanted, these kept coming up in discussions, so I wrote 'em down:

Cam: --------Duration @ .050------------- Lift: ------------- LSA

L-98-------------- 207 – 213----------.415 / .430------------117
ZZ-4 --------------208 – 221--------- .474 / .510------------112
LT-4 Hotcam-------218 – 228----------.525 / .525 (w1.6)----112
ZZ-9 --------------212 - 226 ---------.483 / .520------------112
ZZ-409------------226 – 226----------.520 / .520------------112
ZZ-9X-------------225 – 240----------.525 / .558------------112
ZZ-X--------------239 – 239----------.558 / .558------------112
LPE-211/219-------211 – 219----------.499 / .525------------112
LPE-219/219-------219 – 219----------.525 / .525------------112
LPE-215/220-------215 – 220----------.499 / .510------------112

Brisk

iTrader: (25)

Any boy am I glad I listened to Glenn, he's definatly an experienced and intelligent individual. Thanks again for all the advice you've given me and the friendship that grew because of this.

I just hope I didn't mess up by purchasing my new induction system against Glenn's advice :crossfingers:

Abubaca

iTrader: (3)

....not to doubt, but rather just tryin' to learn.... ....do you have any dyno numbers on that 305 Hotcam to suggest it's a good cam? Why does Glenn think it's a good cam? My opinion, and I'm no expert, would be that it's a tad big. The 305 breathe's a smidge better than that 350, but it's still a torquey TPI, and the hotcam is still a higher reving cam. Again, everything is subject to opinions, and I'm no expert, I'm just curious.

Grim Reaper

Abubaca, I'm just a 50+ y.o. fart whose made a LOT of mistakes in the past. Before DeskTop Dyno (which is okay butnot great), I had access to a variety of old, but expensive (at-the-time) "DOS BASED" dyno simulations from some engine builders who's specialties were custom cams.

Back in the early-mid 1990s, I was doing a variety of comparisons on my own engine with those programs trying to find a good combo. This is before I stumbled across TGO in the late 1990s and found a group of guys with the same goals. I remember when TPIS' "Insider Hints" was big news.

It was through those simulator programs I started to realize the interactions of the Intake, Heads, Cams & Exhaust and how to best match and how to select a cam to compensate for a weakness of some component (ie. a poor exhaust system could be compensated by increasing exhaust duration of the cam or a poor intake could be compensated by increasing the intake duration...conversely, a great exhaust (or intake) could allow for a decrease in the cam's duration).

This was important, because the ECM/eprom still hadn't been cracked so tuning was limited to a few companies who charged outrageous prices with mediocre results, or using "mechanical/electrical tricks" such as the AFPR, rheostats on the CTS or MAT, etc to tune. You just could not get too wild on the cam and have a good running engine if you kept EFI - so cam selection was key.

An interesting combo that always showed impressive results when I played with the TPI intake was reverse pattern cams. Pity that these are all custom and quite expensive. 224/218 is a great cam for TPI - but it's cost prohibitive.

The second best cams seem to be single pattern cams for TPI. Something I've always noticed about the Lingfelter recommended cams for TPI cars such as the LPE 219/219.

BTW, TPIS' ZZ-9 cam with its much longer duration on the exhaust than the intake (compared to typcial cams for SBCs) is not an accident. I've surmised that TPIS always intended this cam it to be a match with the Miniram. The short intake duration promotes low-end torque (a Miniram weakness) while the longer exhaust duration promotes higher rpm scavenging (where the Miniram likes to run).

There is a definite pattern to this madness once you start reading between the lines.

The only problem with cam selection; once most guys begin to modify their engines, they typically replace or modify the TPI system. Due to the unique characteristics of the TPI intake, an optimal cam for the TPI system will not be optimal should they change intakes.

If a person was STICKING with TPI, I would strongly encourage a single pattern cam similar to the LPE 219/219. But, if there is any chance they may modify or replace the TPI intake, they should go with the common dual pattern cam (or be prepared to swap to a better matched cam).

Abubaca

iTrader: (3)

Wonderful post. Thanks.

....it too have noticed trends in "recommended" cams for different intakes. We could discuss the theory of TPI cams for days, but I doubt either of us have the time, and unfortunately, my opinions are mostly theoretical due to my relative inexperience.

The point is though, as always, whether it be rear gears, cams, heads, intakes, torque converters or even transmissions, it has to all be designed to work.

....my opinion though, contrary to you, is that a fully modified TPI still would benefit from a TPI friendly cam. The principles are still the same. I don't care how hogged out it is, is still behaves like a TPI. High port velocity, poor maximum overall flow. Hence your idea of a single pattern cam would still be beneficial. Not that I agree or disagree with single pattern cams being TPI friendly, just saying that a ported TPI still behaves as such IMO.

Everything I've been reading points to the LPE 219 "type" cam being beneficial, although it being a single pattern cam wasn't ever pointed to as to why it excells. Hmmm. I've actually contemplated an LT4 Hotcam, but only running a 1.5 rocker on the intake. That'd make for a 218/228 - .492/.525 cam. Basically the ZZ9 is step up from the ZZ4. Same charachteristics, just bigger. This cam would be an almost exact step up from the ZZ9. Both previous cams have been proven TPI cams. A fully ported TPI with some ETEC 170s and that cam? Hmmm. Can't ya tell I've thought about this before?

Grim Reaper

I think I may have given you an incorrect impression. I completely agree with the above statement; if a person wishes to retain the TPI system, they most definitely would get better performance with a "TPI friendly" cam over the stock. I'm just pointing out some cams I have come across that are TPI friendly that people overlook.

I also agree that modified TPI intake (Large tubes & base) will behave as a stock intake - just making more TQ all over up to the 5,000 rpm area (and usually extend it a bit further as well - but not too much).

As for the Hot Cam, try playing with the 1.6 rockers too. You might be surprised that it benefits more from 1.6s on the intake than the exhaust. Playing with rockers are one of the few "fun things" you can play with that is quick and simple to try.

dave-92gta

iTrader: (1)

sorry, newb here, but can you expain single pattern and dual pattern cam. why is the single patter better?

Abubaca

iTrader: (3)

Single pattern = Intake and exhaust lobes share the same specs or "pattern"
LPE 219 cam = 219 intake / 219 exhaust

Dual pattern = Exhaust lobes are bigger than intake (typically) so you have one pattern for the intake and one for the intake, hence "dual".
LT4 Hotcam = 218 intake / 228 exhaust

If you'll allow me to make a broad generalization, old school cams were mostly single pattern cams. With new head technology and airflow, and engine tuneability, we can really take advantage of the extra flow of more exhaust duration and lift, so a "dual" pattern becomes advantageous. That being said, every single engine has different quirks, habits, and characterstics, but overall, that's the difference.

Now, why grim reaper recommends a single pattern cam specifically for a TPI, I think it's just based on his experience. I'm not sure why per se.

Grim Reaper

The reason I advocate single pattern for TPI, the extra duration on the intake side helps make extra power at the top end (when the TPI starts to choke up), while the shorter duration on the exhaust helps maintain low end torque.

I will explain this both ways comparing two different cams to the LPE 219 (which is a single pattern cam).

First, lets compare the ZZ4 to the LPE 219. The LPE 219 has 2* less duration on the exhaust than the ZZ4 but 11* more duration on the intake. This extra duration on the intake greatly helps the TPI at higher rpms as the TPI starts to choke off the air flow. Thus the LPE 219 should make more power and have a better top end than the ZZ4 while not sacrificing too much torque on the bottom end compared to the ZZ4.

Second, let's compare the LT4 Hot Cam (with 1.6 RRs) to the LPE 219 cam. Both are very similar on the intake side, (the LPE is 1* more), but the LPE has a 9* less duration on the exhaust. The LPE should maintain better bottom end torque than the LT4 Hot Cam because of the shorter exhaust duration as well have a better vacuum at idle. The LT4 will produce a bit more power at the top end.

Lastly, going any much bigger than the LPE 219 starts to have detrimental results for TPI as it moves the power band too high up beyond where the TPI performs - thus you don't produce the power you should because the TPI is choking too much. While at the same time, you start to loose bottom end torque without any payback at the top end. Now you are getting into a "mis-matched" cam. Siamesed runners (or different intake), better heads & better exhaust would be needed at this point.

If anyone has Desk Top Dyno, they can play with these numbers. In the past, DTD was limited on the "intakes" it was able to emulate - but I do believe it is able to emulate a stock TPI intake. Heads, displacement & exhaust will also affect the equation. But DTD should show what I am saying.

Lastly, your Head's Intake to Exhaust Ratio is another key component that needs to be considered with cam selection. For this discussion, I was considering either the stock heads, mildly ported or aluminum L98 heads. If a person were to have something like TFS or AFRs, they would have a great effect and would most likely result in differing results. But, for now, I am trying to keep this a "TPI Intake" discussion.

Grim Reaper

BTW, have any of you guys checked out mw66nova? He's got a 305 with a 230/230 @ .050 cam. Though I believe he using a carb, he is run 12.3s in the 1/4. That's not to shabby for a naturally aspirated 305.

I wish I could talk him into converting to EFI and use a Miniram. I just love it when someone "breaks the rules" and builds something everyone says DON'T.

1989GTATransAm

iTrader: (3)

He must be winding that 305 to the moon. I wonder what his shift points are?