Intake swap thought

[L31MaxExpress]

I had you pegged as a long runner guy.

Its not exactly a short runner. 6" long runners from what others have measured then the head has 5" long runners itself. My TPI setup years ago ended up with siamese ported SLP runners to shorten them. I measured the Vortec intake runner length when I ported my lower manifold. I forget the exact measurements, but I want to say the top was like 6.5" and the bottom was 7.5" for an average of 7".

 

[yevgenievich]

How do you estimate that map value is representative of the flow restriction? Was looking at my logs and at 4200rpm my flow rate is maxed out at 42lb/min, while map value remains in 97-98 kpa and it remains there up to 5k rpm while flow rate is still steady 42 lb/min

 

[L31MaxExpress]

I was looking for one to run on bbc, but nowhere in stock. But in my case now trying to find one that is set up for a tall deck. Interested in results. My air flow maxes out at 4300rpm

They make spacers to use a short deck intake on a tall deck block, but that messes with the distributor mounting height.

My airflow maxes out at 5,300-5,350 rpm. It varies a little run to run. I only see about 10 gm/sec difference between 5,000 and 6,000 rpm. Just flat lines at 5,300ish.

I have a feeling my airflow stall is almost all intake manifold vacuum buildup. All because of that stupid air inlet elbow. The MAP sits at 97 KPA at 6,000 rpm with a near open throttle body.

On a 99 KPA baro reading.
3,500 rpm = 94.9 KPA
4,000 rpm = 93.1 KPA
4,500 rpm = 91.0 KPA
5,000 rpm = 91.0 KPA
5,500 rpm = 88.8 kPA
6,000 rpm = 88.2 KPA

 

[yevgenievich]

They make spacers to use a short deck intake on a tall deck block, but that messes with the distributor mounting height.

My airflow maxes out at 5,300-5,350 rpm. It varies a little run to run.

I am currently running spacers with stock intake, had to retorque lower manifold and still suspecting possibly leak due to fuel trim imbalance code. With current spacer experience, I think getting intake made for a tall deck is better. But the only tall deck intakes that are really out there are single plane style that would use a 90* turn hat instead of a top mount carb or efi system. Not sure how that will work. And intake runners end up being shorter

 

[L31MaxExpress]

How do you estimate that map value is representative of the flow restriction? Was looking at my logs and at 4200rpm my flow rate is maxed out at 42lb/min, while map value remains in 97-98 kpa and it remains there up to 5k rpm while flow rate is still steady 42 lb/min

MAP value is indicative of air pressure in the manifold. Same as if you partially closed the throttle. The engine would make the most power with atmospheric pressure in the manifold. Any drop in MAP indicates a flow restriction. The lower the MAP drops the less dense the air in the manifold. That pressure drop is equivalent to operating at 4,000 ft above sea level. For each 1,000 ft of elevation increase an engine loses about 3% output.

 

[Supercharged111]

Didn't you port the stocker to pass a visual? Will this fly for that or did something change?

 

[0xDEADBEEF]

Its not exactly a short runner. 6" long runners from what others have measured then the head has 5" long runners itself. My TPI setup years ago ended up with siamese ported SLP runners to shorten them. I measured the Vortec intake runner length when I ported my lower manifold. I forget the exact measurements, but I want to say the top was like 6.5" and the bottom was 7.5" for an average of 7".

I wouldn't call it short runner either, but I think it's going to hurt your low end torque a little bit, which it sounded like was a priority for you. Be interesting to see the before and after numbers.

 

[yevgenievich]

MAP value is indicative of air pressure in the manifold. Same as if you partially closed the throttle. The engine would make the most power with atmospheric pressure in the manifold. Any drop in MAP indicates a flow restriction. The lower the MAP drops the less dense the air in the manifold. That pressure drop is equivalent to operating at 4,000 ft above sea level. For each 1,000 ft of elevation increase an engine loses about 3% output.

I am more of trying to make sense of map vs maf and how each and together indicate the type of restriction. On my runs, map does not show a restriction while according to maf sensor it hits a wall in air flow. On your set up sounds like air flow is good until much higher while map starts to indicate pressure drop

 

[L31MaxExpress]

Didn't you port the stocker to pass a visual? Will this fly for that or did something change?

The thing that changed is the van can have antique plates. Good for 5 years and no inspection now.

 

[L31MaxExpress]

I am more of trying to make sense of map vs maf and how each and together indicate the type of restriction. On my runs, map does not show a restriction while according to maf sensor it hits a wall in air flow. On your set up sounds like air flow is good until much higher while map starts to indicate pressure drop

Oh gotcha. Basically if the airflow levels out or drops off and the MAP is steady the restriction is after the plenum. If the MAP drops it is before the plenum. A restriction after the plenum could be cam timing, cylinder head flow, intake port flow, intake port length or even exhaust restriction. My restriction is ahead of the throttle body. I pinpointed it by running speed density and removing intake parts until I found it.