N/A motor talk. Thinking about CFM, Cam Specs, etc.

[BruceH]

I've touched on these things before so forgive me if some of this seems familiar. It's Saturday night, I'm not a drinker, and this stuff is running around in my mind so I might as well put it down and get some input.

I'd really like to hear from motor guys who understand airflow through the motor.

Quick recap: Motor is based on a Big Bore block. 3.701 x 3.750 = 322 cubic inches. FRPP cnc heads that are supposed to flow 273 cfm at .500" lift, 12:1 compression, and these cams:




Equipped with Mac LT headers, high flow cats, FRPP intake with 62mm tb, and C&L racer cai it made 438/389 rwhp/tq. This was with E85.

It now has JBA equal length shorty headers, stock cats, stock tb and intake manifold with a Bullitt cai. With E85 it made 397/390. A loss of 40rwhp.

The dyno for both setups looks pretty much the same until about 5100rpm. That's when the current setup loses steam and the previous setup takes off.



Even though I have no use for the extra power I find myself wanting to get back some of what was lost, maybe more. One way would be to put the aforementioned items back on and be done with it. That's not what I'm thinking though.

I've ordered an offroad h-pipe and high flow cats. These are the same high flow cats I used with the LT headers. Previous high flow cat tests with a different motor yielded 0 gains vs stock cats. However, that was with a smaller motor.

I'm going to start with the cats. More will probably be added depending on the results.

Something is limiting airflow through the motor, it could be part of the intake setup, it could be part of the exhaust. I really wonder what the stock intake manifold is capable of supporting n/a?

How much hp will a stock twin bore 55mm tb support? I've read that it flows 875cfm, I've also read that the Bullitt cai has been flowed and tested out at around 850cfm. I'm thinking that 850cfm should support all of the airflow a naturally aspirated 322 cubic inch motor can consume but I don't have a solid source for the info.

I'm also thinking that longer duration cams with a slightly tighter lsa should help with higher rpm airflow. The 3.750" stroke is sucking air in longer than a stock 3.554" stroke so more duration should allow for more air during that longer stroke.

It gets tricky trying to decide when it's too much. A tighter lsa should allow for some scavaging at higher rpms but again there is a point where it would be too much. For all I know it might be pretty hard to improve on the cams that are in the car right now. They are locked at 108 icl and that is a compromise between a good low rpm icl of 102 and higher rpm icl of 112. Enabling the vct should help on both ends of the rpms but how much?

 

[BruceH]

Doing more internal combustion engine research. The current point of research is air velocity to the combustion chamber.

I'm almost to the point of believing that the 55mm tb is ideally suited to how much air a mod motor can suck in n/a. What I'm reading is that a properly sized tb will keep the airflow velocity where it needs to be for power production and driveability. Go too big and airflow velocity is reduced. This in turn effects airflow into the combustion chamber along with efficiency and power in all except for the higher rpms. Once the airflow velocity is high enough to supply the cylinder properly the larger tb will only equal the smaller one in power production, never will it outperform a properly sized tb.

I wonder if this is part of why I saw lower tq and hp numbers with the 62mm tb/frpp intake combo below 5100 rpm? Because of the subsequent slower moving air into the combustion chamber.

The more I think about this the more I think power drop off above 5100rpm is more likely due to either the stock intake manifold and/or exhaust.

I am tempted to try the new Holley intake manifold. It appears to have a straight shot from the plenum to the head. What I don't know is how well that would improve things, if at all.

Forced induction really is the easiest and most efficient way to make power. Force air through all the restrictions and supply enough fuel for the increased atmosphere and airflow.

 

[weather man]

That Holley manifold is a complete turd from what I have been reading Bruce.

 

[Speedboosted]

I'm not sure how much of a help this is, but Brian Bogdon swapped from the FRPP intake tube to the Steeda intake tube on his FR500S and picked up power everywhere, most notably in the mid range. That was the only change. At higher RPM's it was pretty much a wash (2 or 3hp) but as much as 11-12hp in the middle. Maybe the Bullitt intake is holding the big bore motor back slightly? Could also grab a stock t500 throttle body, port it a little and enlarge the holes, then toss it on as well and see what happens.

 

[svtadam27]

I would place my money on the fact that the Frpp intake having 9.5inch runners compared to the 14 inches runner of the stock manifold is a large part of the power gain in the upper rpm.

As far as the twin 62mm throttle body being too big causing loss of port velocity I just don't see it. The Cylinder head intake runner and intake manifold design are going to determin port velocity. Imo

If my memory serves me correctly, back in the day Anderson ford motorsports did testing with throttle body sizes on a 302-306inch 5.0 from the stock size to 70-75-80-90 and It stopped making any significant power gains with the 75mm but never lost any power or tq with the 80 or 90.

 

[BruceH]

If my memory serves me correctly, back in the day Anderson ford motorsports did testing with throttle body sizes on a 302-306inch 5.0 from the stock size to 70-75-80-90 and It stopped making any significant power gains with the 75mm but never lost any power or tq with the 80 or 90.

Peak power and torque only? Everything I've looked at concerning sizing carbs shows significant losses at lower rpms in both hp and torque with a carb that is too large. Once the rpms get in the higher ranges is where the difference levels out to about zero.

By any chance do you have dyno sheets of your own with comparisons between different sized throttle bodies with an otherwise same setup? I can read magazine articles but I place a higher value on what someone has seen for themselves. IMO most of the car mag articles are written for companies who spend the most advertising money with the mag. This in turn leads to articles that are designed to sell products and services from the company who paid to have the "article" written on their shop.

I'm coming up with high 800's for cfm on both the stock twin bore 55mm and a single bore 80mm. Everything I can find says that this level of airflow will support high 500's fwhp n/a.

If this is a fact then it should be plenty for my 322 inch motor. The most I've made with it n/a is 438rhwp uncorrected which is probably low 500's fwhp.

I do know that going to a larger tb has made low speed, in traffic driveability and idle quality tougher to tune. More airflow with less blade angle = less precise throttle and airflow compensation inputs.

To me that rules out the stock tb as a source of restriction. I'm also thinking back to carburetor days and can remember that a 750cfm would support just about anything that could still drive on the roads. I realize that this is a pretty general statement.

Thanks for the input.

 

[weather man]

Peak power and torque only? Everything I've looked at concerning sizing carbs shows significant losses at lower rpms in both hp and torque with a carb that is too large. Once the rpms get in the higher ranges is where the difference levels out to about zero.of airflow will support high 500's fwhp n/a.


Thanks for the input.

Carbs are hard to compare to fuel injection. A to big carb will run like crap because they can't pull and vaporize the fuel properly at low rpm/part throttle. Saw this all the time on sleds and bikes.

 

[svtadam27]

Carbs are a different animal then fi.

I'm still running the factory throttle body for now Bruce, I did just buy a frpp one so hopefully it'll be here next week. If I get a chance I may dyno it at the same place I did last time and compare the differences. Might see if they'll let me change the out while the cars on the dyno. I do agree that too large of a throttle body could cause drive ability issues.

 

[BruceH]

That Holley manifold is a complete turd from what I have been reading Bruce.

I've read the same. It might of been a case of one bad part though. If I purchase from Summit or Jegs I have confidence they will take it back if it's made poorly.

Carbs are hard to compare to fuel injection. A to big carb will run like crap because they can't pull and vaporize the fuel properly at low rpm/part throttle. Saw this all the time on sleds and bikes.

Very true, airflow speed won't have an effect on fuel atomization with fuel injection. HP supported by cfm should still be similar though. All I can come up with is that 1.5cfm will support roughly 1hp n/a. If this is so then the 825cfm of the Bullitt cai should still support my motor, along with the 875cfm tb. It's one of my main concerns because there are a whole lot of "rule of thumb" things that don't always pan out.

For instance, I'd hate to change out everything else and discover that a GT500 tb and larger cai would of given the biggest gain. On the flip side I'd hate to change those components out only to lose driveability without a measureable gain in power.

Carbs are a different animal then fi.
I'm still running the factory throttle body for now Bruce, I did just buy a frpp one so hopefully it'll be here next week. If I get a chance I may dyno it at the same place I did last time and compare the differences. Might see if they'll let me change the out while the cars on the dyno. I do agree that too large of a throttle body could cause drive ability issues.

That would be useful info. They shouldn't have too much of a problem letting you swap the tb while the new tune loads.

 

[Boone]

Your dyno results definitely indicate a lack of airflow on the top end. Once my motor is broken in, I'll post my dyno results for you to see. Our motors are very similar. Also, I am still running the stock twin 55 TB on my car.

My first guess on your power loss is a lack of scavenging in the cylinders due to going from LTs to shorties. I know the intake pieces are the most simple items to swap, but I believe you will find you can't get any more fuel/air into the cylinder until you get enough of the spent gasses out.

If you want to attack the incoming air issue, I believe your most bang for your buck is available by replacing the stock intake. The comparisons I've seen show the aftermarket intakes to be worthless until the upper rpm range, which is precisely where your results begin to fall off.

 

[Pentalab]

"Equipped with Mac LT headers, high flow cats, FRPP intake with 62mm tb, and C&L racer cai it made 438/389 rwhp/tq. This was with E85.

It now has JBA equal length shorty headers, stock cats, stock tb and intake manifold with a Bullitt cai. With E85 it made 397/390. A loss of 40rwhp.

The dyno for both setups looks pretty much the same until about 5100rpm. That's when the current setup loses steam and the previous setup takes off."
....................................................................................................................

## Why did you remove all the good stuff ? I can't see the twin 62mm being too big at lower rpms. Sure, the bigger tb will pass more airflow for a given blade setting, but the correct new tune will compensate for that effect.

Do you now have the stock H in there ? Stock H has that disc with the hole in it. Looking at the dyno plots...it appears to run out of air > 5100 rpm. But I can't see tuned shorties being 41 hp down from LT's..that's a bunch. Best guess is the shorties are causing some loss..and the cai is causing the rest. The smaller tb might lose a tiny bit at the top end. It all adds up. The CAI swap would be easier than a exhaust modification.

 

[RED09GT]

It's too bad no one makes an intake manifold that slots between the stocker and the FRPP. I think you are at the limit of the ram tuning of the stock manifold but there may be some power hiding in a few of the production compromises in the intake design. A few people tried porting out the throttle body entrance and radiusing the transition into the plenum on the stocker early on but no one tried it on anything more than a stock displacement motor.
I did it with mine but I basically have a stock motor with a turbo, so everything is pretty much out of the window anyways.

 

[BruceH]

"Equipped with Mac LT headers, high flow cats, FRPP intake with 62mm tb, and C&L racer cai it made 438/389 rwhp/tq. This was with E85.

It now has JBA equal length shorty headers, stock cats, stock tb and intake manifold with a Bullitt cai. With E85 it made 397/390. A loss of 40rwhp.

The dyno for both setups looks pretty much the same until about 5100rpm. That's when the current setup loses steam and the previous setup takes off."
....................................................................................................................

## Why did you remove all the good stuff ? I can't see the twin 62mm being too big at lower rpms. Sure, the bigger tb will pass more airflow for a given blade setting, but the correct new tune will compensate for that effect.

Do you now have the stock H in there ? Stock H has that disc with the hole in it. Looking at the dyno plots...it appears to run out of air > 5100 rpm. But I can't see tuned shorties being 41 hp down from LT's..that's a bunch. Best guess is the shorties are causing some loss..and the cai is causing the rest. The smaller tb might lose a tiny bit at the top end. It all adds up. The CAI swap would be easier than a exhaust modification.

FWIW I've made 699rwhp with the stock cats. That was with a .030 over 4.6 and Procharger at 19psi fueled by E85 but the point is that it was made with stock cats.

A few years ago I swapped the stock cats for a Magnaflow high flow x-pipe. Changed nothing else and hp was exactly the same. This was with a n/a 4.6. IMO the x-pipe sounded horrible so I went back to the factory h pipe.

I'm not sure where the loss is coming from. It's probably a combo of all the changes. I know that Mac LT's are good for some power with a 4.6 so I'd imagine that not having them with a 5.3 isn't helping.

I took the other parts off when I went with a DOB setup. When the DOB came off I had already sold the previous parts. Got a great deal on the JBA equal length shorties.

What really gets me is how my logged airflow just peaks at the same time as the hp. Either air coming in is being limited or air coming out is being limited or it's a combination of both.

It's too bad no one makes an intake manifold that slots between the stocker and the FRPP. I think you are at the limit of the ram tuning of the stock manifold but there may be some power hiding in a few of the production compromises in the intake design. A few people tried porting out the throttle body entrance and radiusing the transition into the plenum on the stocker early on but no one tried it on anything more than a stock displacement motor.
I did it with mine but I basically have a stock motor with a turbo, so everything is pretty much out of the window anyways.

This is why I'm thinking about the Holley intake. It would be nice to know what to expect from it performance wise though.

 

[eighty6gt]

Bruce, you're a lucky guy to be able to try all of this cool stuff. I bet the car drives great as-is.

Were it me I'd change as little as possible, and it would cost a fortune. I think the Holley intake and a GT500 throttle body would be the cheapest option, then dyno from there and do a direct comparison, and if it's awful, get Holley/? to buy the intake back.

I'm in agreement with the other guy that the throttle body isn't much of a factor when it comes to ram tuning or cylinder filling.

 

[lito]

I've never seen anyone losing anything due to a bigger throttle, most of the time also haven't seen any gains either but no loses.

 

[eighty6gt]

I bought a $600 throttle body from VMP! It sure looks nice, I feel like a harley guy.

 

[lito]

Your setup is different, yours is working with lower pressure and CFMs drop.

But still, you are probably quite close now compared with what you had before.

Using too much leather and chains these days?

 

[eighty6gt]

lol, yeah, that's where all the $$ is going so I can't buy my fuel system and get the car finished!

 

[BruceH]

The high flow cats h pipe wasn't in stock. I've changed the order to an off road pipe. I'll start there. Still thinking about the Holley intake manifold but not sure why.

FWIW I've ran the 62mm FRPP tb with the FRPP intake manifold, C&L racer cai and didn't have any issues. I did have issues with a GT500 tb, stock intake manifold, and JLT 3 cai. What would happen is the motor would go into failsafe every now and then. It was always when I was letting off the throttle during normal driving with light throttle.

The same tb worked just fine with a different setup. I think it had something to do with the combo of intake components and air metering at normal driving, low rpm airflows. Maybe there was just enough air post maf during the transition from light throttle to closed tb to confuse the ecu? I really don't know but that specific combo is the only one to give me any type of troubles I couldn't figure out.

Anyway, once the orh comes I'll go to the same dyno as the previous runs were made and report sae corrected numbers.

I've also started to snap up good deals on DOB parts when they pop up, just in case, lol.

 

[Boone]

Just can't leave well enough alone can you Bruce. You were my motivation to stay NA and be patient with my 5.3 setup. Now here you go again... and I can't wait to see what comes of it. Thanks for sharing all the things you try. I respect your objectivity.