TKO500

iTrader: (5)

I am nearing the end of the build on my motor. Originally I was going to run the stock throttle body with the airfoil but now I am wondering if I should go larger.

My motor is as follows:
91 SD TPI 350 .030" over
Trickflow 195cc heads w/1.6 TF roller rockers
LT4 Hot Cam
Edelbrock TPI base and runners
24lb injectors and AFPR

I suppose the largest I would want to go is a 52mm. Will the 48mm suffice? If I do not need to run the 52mm I wouldnt mind saving the money for something else.

What does everyone think?

Merlin

Strange, isn't it, that the 502 RamJet engines are making 500+HP and 530 ft/lb through a 48mm throttle body, just like yours. Perhaps you should consider going a little smaller to maintain a similar cubic inch/throttle body ratio.

Formula350Scott

iTrader: (3)

Will someone please dyno their car with a 48mm vs 52mm vs 58mm TB back to back? We need more facts. I'm sure they benefit from bigger TB's. Every other car on the road does. My friend has a 3.5 litre dodge intrepid and it has two 52mm TB's from the factory. Surely an engine thats 2.2 litres larger would use at least the same size throttle bodies. All im saying is we need more info on what works and what doesnt.

89Nighthawk

52 mm is all you need. If you were pushing a LOT more CID and a LOT more RPM then you might need the 58. But you'll be fine with a 52.

TKO500

iTrader: (5)

Does anyone think the stock 48mm throttle body will suffice?

Most likely this car will never see more than 5500 rpm's since I know I wont make power past there anyway.

If I can run the 48mm throttle body I most definately will

Mkos1980

iTrader: (8)

I use a 48 on my 383. TF Head 219 cam. Edel base ASM Runners

doc

Some flow data below:
(flow @ 28.0" water)

·Stock TPI/LT1 48mm Throttle Body w/o airfoil -- 783.0 cfm
·Stock TPI/LT1 48mm Throttle Body w/ airfoil ---- 821.9 cfm
·TPI/LT1 52mm Throttle Body w/o airfoil ---------- 848.9 cfm
·TPI/LT1 52mm Throttle Body w/ airfoil ------------ 898.8 cfm

The stock twin 48mm TB with an airfoil is good for about 632Hp at the flywheel (it takes about 1.3 CFM to make 1 Hp). But bigger will not hurt you. So, just to make yourself feel better, get the 52mm or even the 58mm TB. I'm running the 52mm on my 395 cu.in. stroker.

Your main restriction is the intake base. It would probably be more cost effective to port the intake base along with the runners.

Vader

"Conventional wisdom" might suggest that "bigger is better", but the dyno doesn't always prove that out. An example is soemthing I fought in LT1s. Dyno numbers defied "conventional wisdom" and showed about an 8HP increase by using 2½" exhaust pipes in place of 2-3/4" pipes along the length of the vehicle. I know the analogy from exhaust to intake is not comparable, but the philosophy that "bigger is better" doesn't always hold true.

Instead of dropping a few Franklins on a bolt-on that probably won't yield results, spend it on something that will. With little doubt, the bolt-on is faster and easier than any real, substantial work that will make an improvement, but you might just as well put on stickers, since the effect is the same. It makes you feel better, even if the numbers don't improve.

FWIW, comparing a short-stroke, 215-ish inch French/Dodge engine that needs to rev t0 6,500 RPM to make respectable peak horsepower numbers is quite different than something that makes real power down low (torque peak at 2,800 RPM instead of 4,000), and produces peak HP nearer to the reality-based, formula-defined RPM of 5,250. The old Chevy 283 could make over 250HP N/A and lasted forever, and made more torque across a wider RPM range. It used a two-barrel Rochester (2GC). High RPM HP is great if you can use it. You can almost never use it on the street or strip. If you run oval track, that's a different story, but you'll likely not be using a Renault/Dodge V-6 when you compete.

With litle doubt, you need to move air to make power, but the TB may not be your most restrictive part.

Formula350Scott

iTrader: (3)

Allpar.com

When introduced in 1993, the 3.5 was the most powerful, naturally-aspirated engine available in any Chrysler-built sedan, with peak horsepower of 214 at 5,800 rpm and 221 foot pounds of torque at 2,800 rpm (it would eventually go to over 250 horsepower). Mechanical noise levels were the lowest of any engine ever measured by Chrysler.

221 ftlbs of torque @ 2800 rpm is power down low.

With his heads, cam and intake, even though its still LTR, I think he'd benefit from a 52mm tb. I dont think he'd get more than 10hp out of it but thats for him to decide if its worth the money.

cuisinartvette

Absolutely, save your money- youll see 0 difference except a lighter wallet.

Shagwell

I'm running 11's w/ a 750 carb. Your stock TB flows 780, and it is only moving air, not air and fuel. - Even according to Holley, my 750 is pretty ideal for my 355 turning 7200 r's. - So why would you need more cfm than 780?

- also, a buddy of mine has everything imaginable done to a 2-valve 4.6 mustang(all motor). Fully ported heads, cams, full exhaust, aftermarket rods/pistons, etc... 331rwhp/300rwftlbs out of 281 cubes, all-motor. Until the last/final head port job, he lost power and throttle response going to an aftermarket(larger) TB.
- I know it's a mustang/totally different engine, but still...

YenkoST

iTrader: (5)

Carb is a little different than fuel injection though.

In the latest CHP magazine, they did a test on a stock LT1 from a 48 to 52mm test and a SLP cold air package and made 15.5 rwhp and 9 ft lbs of torque then added more fuel to then now lean condition and made another 17.5 rwhp and 14.25 lbs of torque. So, take it with a grain of salt. I have done a 58mm on my 383 and noticed quite a bit of difference but I don't have a dyno around here so...the old butt likes the extra air. But I am also pushing over 400hp too.

Shagwell

I glanced over the CHP article. I'd like to see side-by side curves. - Atleast w/ efi if you go over, it's not as drastic of a throttle response loss.

IROCZZ3

Many years ago I went from a 48mm to 58mm TB and gained 2 mph in the quarter on a hotter track day with no other changes. But I did have a head/cam, Superrammed motor so take it for what it's worth. Not much of a gain but that was expected.

I still believe a bigger TB helps only if you've done heads/cam/intake mods. Other than that it certainly would NOT be the first mod to do and is money better spent elsewhere.

If you've done the major mods I would just go straight to a 58mm TB and be done with it. It doesn't cost much more and you'll never ever second guess yourself if the 52mm you just bought is too small. No sense in spending money twice because I know lots of people have done that.

Also I never had problems with throttle response from the bigger TB. Some have but I think it's in the tune that makes the difference.

doc

IROCZZ3, I agree with you completely, thats a good post.