Intake runner length for low RPM port injection

[gmrocket]

Trying to get a rough idea of how important total intake length needs to be from valve to plenum. This is for a low RPM tq deal ,, hauling a load at all times. RPM range 1500 to 4500 max. Cruise RPM in the 2000 to 2300 range

V8, 380 to 400 cubes, port injection with injectors approx 4 1/2" from valve.

I want maximum TQ....any formulas I can use?

I recently dynoed 2 tow engines. Both had conventional dual planes so not sure I'd have any info on runner length, but it was interesting to see engines in that rpm range on the dyno.

Both 355 cubes. One pulled from 3000-6000 rpm the other 2000-5000 rpm.

The one pulled from 2000-5000 is a real oddity.

I could post info if your interested.

Randy

Yes I would be interested Randy.

What kind of low end TQ?

[Newold1]

My take on a pretty simple solution:

Bore: 4.125"
Stroke 3.750"
Compression 10.250"
Rod: 6.10"
Cam: 210 I @.050", 215" E @ .050" LC 109, LSA 112 , I .500", E .500 nice hydraulic roller installed +3 deg.
Heads 180-1850cc w/2.020" Intake, 1.60" exhaust , aluminum
18-22" intake runners with adequate plenum and a 650 - 750 cfm throttle body

410HP @4800 , 500lb/ft. torque @ 3400rpms and a pretty flat average torque of 450lb/ft. between 2800 and 4200rpms

With good exhaust system and good EFI system tuning this should be ABOUT AS GOOD AS IT GETS and stay close your engine size and requirements and based on these specs. a pretty easy and reasonable cost to build with all off the shelf components.

Your biggest dollars and difficulty will be comong up with an intake system that gets you close to a 18"-22" intake tract length.

Whats your guys thoughts on this idea?

[gmrocket]

Do you think that much compression and short cam with early closing would build too much cylinder pressure?

I would like to keep cranking psi about 175 max so it can run on regular

My initial cam choice is a hydraulic roller, 262 adv intake and 210@ .050 and .505" with 110 lsa

[Newold1]

Cranking compression is not what an engine operates at. The dynamic compression is what really matters. You indicate this is an EFI port injected engine and with a good operating tune it should run on 10% ethanol regular (Esso) without any major problems.

[gmrocket]

Hi cranking psi is a pretty good indicator the engine will be making a lot of cylinder pressure at low rpms . High cranking psi on low rpm towing type engine in my opinion would have trouble running on the 87 octane available at our pumps

it would just build too much cylinder pressure in the low rpm range..then you'll end up taking a bunch of timing out of it

At least that's what I've seen with short cams and higher ratios.

[Newold1]

Your dynamic compression ratio is 9.50 to 1 and with the 87 octane regular with its current 10% ethanol and soon maybe 15% ethanol and the right tune the engine with this sort of build should be good at low rpms on regular.

[BigBlockMopar]

I'm running a pair of those Chrysler Long Ram intakes on a 496ci bigblock Mopar with around 10.5:1 cr on Edelbrock Performer RPM heads and a CompCams XR274R solid roller.

This engine had no issues with its previous pretty much stock-ish hydraulic ft cam, but now with the solid roller, it wants to 'ping' fiercly when giving it too much throttle with a warmed up engine and engine bay (sucking in hot underhood air).

[gmrocket]

I'm running a pair of those Chrysler Long Ram intakes on a 496ci bigblock Mopar with around 10.5:1 cr on Edelbrock Performer RPM heads and a CompCams XR274R solid roller.

This engine had no issues with its previous pretty much stock-ish hydraulic ft cam, but now with the solid roller, it wants to 'ping' fiercly when giving it too much throttle with a warmed up engine and engine bay (sucking in hot underhood)

That's exactly what I don't want to happen

Do you know what your cranking psi is?

[BigBlockMopar]

Never checked this when I built the engine because it had a stockish cam.
The current roller makes more pressure which is now causing troubles.

[F-BIRD'88]

If your plenum(s) on that intake are water heated AND it is also breathing HOT underhood air, why not fix that and stop worrying about cylinder pressure VS camshaft. Fix the real problem. Carbs/plenum getting too hot and breathing hot air too. Freash cool dense ducted air is great for car performance. The water heated plenums probabily need a water shut off valve controlled by temperature ( or manually by you) to get them right. Cool old Chrysler.

[BigBlockMopar]

There's no water going through the plenums. I've left them open.
The factory had either exhaust heat or later water through them. But I've noticed the carbs hanging over the hot headers don't need any heating because everything gets hot enough already after some driving. Water 'cooling' would be nicer.
Also tried slowing the advance curve and backing down timing but that didn't work and the engine only got hot as a result.
Header wrap/coating or heatshielding AND cold air intake will really help this setup as the engine doesn't detonate as long as the engine bay is cold enough.

[F-BIRD'88]

Do not hwader wrap.. But do make shields.

Also make up ducted fresh air system.
May want to install a chin spoiler on the car too.
Improved cooling.

When you do shield the plenums from excess header heat
you may well want water heated plenums (with shut off control) for quick street warm up.

You have a (underhood) temp control problem not a cylinder pressure problem.

With the headers I can see you having real carb hot soak issues
without header heat shielding.

Parts/ component system source for fabbing a r ram air cold air ducted system..www.ramairbox.com

Lack of initial base idle timing with that cam will make the headers run HOT @ idle, making hot soak worse.

[pdq67]

Trying to get a rough idea of how important total intake length needs to be from valve to plenum. This is for a low RPM tq deal ,, hauling a load at all times. RPM range 1500 to 4500 max. Cruise RPM in the 2000 to 2300 range

V8, 380 to 400 cubes, port injection with injectors approx 4 1/2" from valve.

I want maximum TQ....any formulas I can use?

I recently dynoed 2 tow engines. Both had conventional dual planes so not sure I'd have any info on runner length, but it was interesting to see engines in that rpm range on the dyno.

Both 355 cubes. One pulled from 3000-6000 rpm the other 2000-5000 rpm.

The one pulled from 2000-5000 is a real oddity.

I could post info if your interested.

Randy

Yes, please post the, "oddball", engine combination.

Thanks,

pdq67

[1989TransAm]

I didn't write it joe; I just posted it. If you have a better one, perhaps you'd like to share. BTW, if it's been so wrong these several years, why have you waited so long to speak up?

In my real world testing I have found that chart to be pretty close with all the custom TPI intake manifolds I have built over the years.

[randy331]

Yes I would be interested Randy.

What kind of low end TQ?

I used a Vortec 350 block bored .030" over and a Eagle 3.48 stroke crank.
Got sealed power hyper pistons with dish that took 1.5 1.5 3 mm rings. Used .030" file fit top at .019 gap.
Used a .020" file fit second and just dropped it in with no filing. It's .025" gap.
Used a .020"over expander under a set of .030 over oil rails for oil ring set.
Short block rotates over at 14 LBs.

The cam is hyd roller GM puts in the 383 HT truck crate engines. Part #14097395
196-206 / 109 LSA .431/.451 lift wiith 1.5 rockers.
Lifters are ls hyd rollers and springs are lS.

The heads are Dart #10024361 that were advertised as 165cc but were 170-171cc with the throat already out to %89.
I ported the heads some and went to a 2.02" Manley valve on intake and stayed 1.5 ex. With 50* seats on both.
Think about the lack of window area with a 196* @ .050" duration cam and .430 lift???
Did quite a bit of porting on ex. They had bad edges where valve job ended as they came from Dart.
Rockers are a set of self guided off Vortec heads.
Performer rpm cause I had 3 of them sittin here.

Dynoed with a 600 vacuum carb, but have went to a 450 vacuum secondary quick fuel.

It made 380 Lbs at 2000 rpm and was right around 400 Lbs from about 2300-3500 rpm or so. Right where the engine will run at hy speeds.
Made a few pulls with just the secondary side closed and it made no difference in power till after 3200 rpm, then was worth about 20 peak HP.

Brought the engine up to 2500 rpm and then added load and throttle till it was producing 100 BLs tq and it was still showing 17 inches manifold vacuum.

Peaks it made 405 LBs at 3000 ish ( hard to tell right where peak tq was cause it's very flat curve there ) and 310 HP at 4900.

Made a couple pulls on out to 5500 rpm and I have never seen an engines power tank so fast in just 500 rpm. LOL

Randy