[charlie66]

Is there anyone here that would know how to check if there boosted motor has the right size plenum for there combination ? I have a friend that has the same size ci motor as me , its actually a little smaller but it has a much larger plenum, and pound for pound of boost he makes a lot more power then me. So I was wondering if that was the reason. He does have a 6 cyl to my 4 and does have 2 intake valves to my one per cylinder but with smaller duration cam. He keeps telling me I should make a bigger plenum, so I just thought I would ask here what you guys think.If the plenum I have turns out to be too small I will make a new manifold.

Thanks....

[Boostedbird]

Increasing the size and reshaping of my intake's plenum was one of my winter Upgrades and I feel that it was well worth the effort. I changed my cloverleaf shaped Victor by porting it to a full Dominator shape and widened and blended the runners a couple of inches in. I swapped the 1" Edelbrock cloverleaf spacer for a HVH Supersucker 1" spacer. I didn't cc the plenum before or after, but there was a good bit of volume added. The shape of the power curve changed on the dyno sheet from the first time that it was on the dyno and this last time, plus it picked up a couple of pounds of boost. In my case I feel that the cloverleaf shape was blocking the ports and it needed more volume anyway. Probably needs more. I don't know if you want to see what I did, but here's some pics if you do.

[Tom Vaught]

Normal "Naturally Aspirated" engines (with carburetors) like plenums that are as big as possible and can still signal the boosters properly. They typically go from a .7 times the engine size to 1.0 times the engine size.

Boosted Engines with carburetors like plenums that are as big and can dissipate flow velocity quickly in the plenum and increase charge density to each runner. They do not need signal to a booster so the runners and the plenum can be sized for best runner lengths and volumes for the power anticipated. They typically go from a 1.0 times the engine size to 2.0 times the engine size. The engine will run with a smaller plenum but will choke up quicker at high air flow rates later in the rpm of the engine.

Marty Palbykin had a custom TR Intake Manifold for his 406 CID Twin Turbo Engine that was 2.0 times engine displacement and the vehicle would still do a 1.02 sixty foot time and run 206 mph and a Elapse Time of 6.96 (in 1996, many years ago).

Marty, Mary, and I came up with that intake.

Charlie and I have discussed the larger Plenum Volume deal on his 4 cylinder Intake. several times but Charlie was learning about Boost Pressure effects, not Intake Manifold Design for Boosted Engines.

You can make good power with a smaller plenum but you really need to be on your game with the cylinder to cylinder air distribution to make the best power.

My Boosted EFI Intake has a big plenum, Pictures posted in the past, "for a reason"

Tom V.

[p4msi1]

Thanks Tom,
For the technical information. You certainly have been a huge help to us.

Steve

[twooldgoats]

Originally Posted by Tom Vaught

....

You can make good power with a smaller plenum but you really need to be on your game with the cylinder to cylinder air distribution to make the best power.

...

Tom V.

So true. Even though my supercharger and mechanical fuel injection combination is crude in many respects, by checking EGT's for every cylinder and running port injectors, I can tune by cylinder and make max power at any given blower overdrive or air density level. I run smaller injectors toward the rear of the engine to compensate for those differences. I don't pay much attention to boost numbers. Too many unrelated factors can affect boost levels.

Jim

[TimeWarp]

Originally Posted by twooldgoats

I don't pay much attention to boost numbers. Too many unrelated factors can affect boost levels.

Jim

This is also very true, although I would say those factors are all related. Boost is really just a measure of restriction before entering your cylinders. Really the only thing boost numbers are good for is to evaluate what your engine, turbo(s) and intake tract are doing and whether changes you make have the desired effect. For example, by adding heads that flow better, and changing nothing else, your boost psi may go down. But that in no way means you are making less power (in and of itself). Too many people look at boost as a static thing and try to evaluate what is going on just by those numbers, when in fact it is just one piece of vital information and more is needed.

[charlie66]

Originally Posted by Boostedbird

Increasing the size and reshaping of my intake's plenum was one of my winter Upgrades and I feel that it was well worth the effort. I changed my cloverleaf shaped Victor by porting it to a full Dominator shape and widened and blended the runners a couple of inches in. I swapped the 1" Edelbrock cloverleaf spacer for a HVH Supersucker 1" spacer. I didn't cc the plenum before or after, but there was a good bit of volume added. The shape of the power curve changed on the dyno sheet from the first time that it was on the dyno and this last time, plus it picked up a couple of pounds of boost. In my case I feel that the cloverleaf shape was blocking the ports and it needed more volume anyway. Probably needs more. I don't know if you want to see what I did, but here's some pics if you do.

Looks good. So you were thinking some what the same thing..

One of the benefits I was thinking
/hoping for was maybe with the extra area in the plenum, that it might lower the intake temp's and add some extra hp...

[Tom McQueen]

I recently switched cylinder heads. So I will need a sheet metal manifold because there are no 'off the shelve' intakes available. Only custom. Talking to someone about the intake and the data in this thread gives me some things to think about.

Keep it going.

[charlie66]

Is there a way we could see some pictures of Martys TR intake?

[Boostedbird]

Originally Posted by charlie66

Looks good. So you were thinking some what the same thing..

One of the benefits I was thinking
/hoping for was maybe with the extra area in the plenum, that it might lower the intake temp's and add some extra hp...

Charlie, I believe that you are right in your thinking. Things like intercoolers, air filters, long runs of piping, small plenums, and tight bends all add restriction to flow, wich stacks the air up and heats it as its compressed. As I was doing my intake I focused on putting as large a radius from the throttle blades to the intake runners as I could get with nothing in the way to give the air time to turn into the ports. Having the 4150 carb on a Dominator intake helped with this. Also made the plenum as wide and large as i could. I'm going to add atleast another 1/4" phenolic spacer under the HVH. Now I can look through the bores of the spacer down through the runners and see into the head ports.I also believe that I seen a little more boost not from restrictions on the intake side, but added volume on the exhaust side. I bought the larger a/r turbine housing to get the whole thing to breath better, but haven't started testing backpressure yet. Just my thinking on it.

[ponjohn]

Shouldn't thee plenum size be equal to or larger than the cubic inch being used?

[Boostedbird]

Tom V. Said 100%-200% as big as the ci on a boosted application.

[charlie66]

Originally Posted by Boostedbird

Charlie, I believe that you are right in your thinking. Things like intercoolers, air filters, long runs of piping, small plenums, and tight bends all add restriction to flow, wich stacks the air up and heats it as its compressed. As I was doing my intake I focused on putting as large a radius from the throttle blades to the intake runners as I could get with nothing in the way to give the air time to turn into the ports. Having the 4150 carb on a Dominator intake helped with this. Also made the plenum as wide and large as i could. I'm going to add atleast another 1/4" phenolic spacer under the HVH. Now I can look through the bores of the spacer down through the runners and see into the head ports.I also believe that I seen a little more boost not from restrictions on the intake side, but added volume on the exhaust side. I bought the larger a/r turbine housing to get the whole thing to breath better, but haven't started testing backpressure yet. Just my thinking on it.

Everything you did im sure helped. Did you check back pressure before you changed the A/R? I now have less exhaust pressure then compressor pressure with the new turbo. Have to say that Precision turbos are really well designed .. Cant wait to get it back on the dyno. I think 30 psi is making the same as the old one at 35 .. Cant prove it , but it feels like it..
What ever happened with your converter? I would have them just tighten it till you cant anymore. haha.

My friends manifold is 1.0 times larger and it works really well. How would I figure what the ratio of my plenum is now to my 198 ci? Does anyone know how to figure this?

[Tom McQueen]

Originally Posted by charlie66

Everything you did im sure helped. Did you check back pressure before you changed the A/R? I now have less exhaust pressure then compressor pressure with the new turbo. Have to say that Precision turbos are really well designed .. Cant wait to get it back on the dyno. I think 30 psi is making the same as the old one at 35 .. Cant prove it , but it feels like it..
What ever happened with your converter? I would have them just tighten it till you cant anymore. haha.

My friends manifold is 1.0 times larger and it works really well. How would I figure what the ratio of my plenum is now to my 198 ci? Does anyone know how to figure this?

Quick and dirty. Measure the length, width and height of the plenum. Subtract the width of the intake material. Multiply LxWxH. This gives ci.

Take the plenum ci and divide it by the ci of the engine. = ratio.

example

Plenum = 6"x7"x4" = 168ci
168ci / 198ci = .85

[Boostedbird]

Charlie, I haven't messed with the turbine housings yet. It still has the 1.23a/r housing on it. The 1.60a/r housing is sitting on the shelf. I'm gonna measure the pressure with the 1.23, then switch and measure again.
I talked to PTC and Lane said that he would take it to the track and get a couple of runs in to see what it'll do before we change it. So I'm gonna try to get to the track next weekend if I can. I've only got the perches about halfway fixed and I want to put some driveshaft loops in there.

[charlie66]

Checking the old housing first is a good idea. Im curious to know what it is. You're not at any real high pressure now so I would think you're good.
If you don't mind me saying , I don't agree with what Lane said. You already know you're slipping by the dyno mph compared to what it really should be at. I would just tighten it up. Why go there and race the car to find out what you already know.... lol

What ever you do that car is going to be really fast.......I think you're doing a great job ironing out all the bugs...

[Boostedbird]

Thank you Charlie! I did go to the track and made two passes tonight. At 3,620lb race weight it went 6.30 at 110mph on 6psi with a wheels up 1.45 60ft. Converter felt real lose. I'm gonna tighten it up. Wold only build 4 psi on the leave, but probably because I was only on 6psi.

[Jack Gifford]

Originally Posted by twooldgoats

... I run smaller injectors toward the rear of the engine to compensate for those differences...

As I did with the blown hemi, since the magneto at the rear ruled out moving the blower back any more (and the hemi rear intake ports are WAY back). But doing that simply acknowledges the need for better air distribution- via a larger plenum or whatever. Off-hand, I think my port nozzle range was as much as #16 rear to #22 front. This could roughly translate to [maybe] a 25% air (and thus power) "deficiency" in the rear cylinders. That's why the blower manifold for my four-cylinder will be almost five times the engine's displacement (with the blower centered on the ports- a special center-outlet billet 14-71).

[charlie66]

Originally Posted by Boostedbird

Thank you Charlie! I did go to the track and made two passes tonight. At 3,620lb race weight it went 6.30 at 110mph on 6psi with a wheels up 1.45 60ft. Converter felt real lose. I'm gonna tighten it up. Wold only build 4 psi on the leave, but probably because I was only on 6psi.

Not bad first time out. That's probably a 10.00 to 9.90 1/4 mile pass. So you made 610 hp at 8.5 and you made this pass on 6psi ? Most likely that was with less then 600 to the wheels that gives me a good idea what mine will run , my car weighs 3400 and made 616. So I guess I should be in the 9's then. Thanks for posting that...

So if all you did was put a spacer on and port the sort turn at the top of the runners then maybe I can try this before I try making a new manifold just to see if I get similar results . A lot less work , hmm worth a shot I think. Thanks again...

[charlie66]

Originally Posted by Tom McQueen

Quick and dirty. Measure the length, width and height of the plenum. Subtract the width of the intake material. Multiply LxWxH. This gives ci.

Take the plenum ci and divide it by the ci of the engine. = ratio.

example

Plenum = 6"x7"x4" = 168ci
168ci / 198ci = .85

Thanks . Ill try figuring this out tomorrow....