This is a 3rd Gen L98 motor with 355CI. My goal is 400RWHP. DynoSim says I can make over 500 flywheel horsepower which will do it with the XFI 218. Real world I'm not so sure and the reason for the post. I already have the XFI218 cam but will sell it if I can do better. I would install the XFI cam 1 degree advanced. I will be using custom 1 3/4" shorty headers with cones etc.

Here are the parameters. Must pass California smog. I want all the power to be in by 6000rpm. I want a decent idle and was thinking low 220's at the most on intake duration. I'm building up a 4 bolt long block to replace what is in the car now so I can do what needs to be done.

So is it posible to reach the 400RWHP. By the way the intake is a very highly modified TPI. Effective runner length is about 12 inches. Intake manifold has been extruded honed and similiar units have flowed 276cfm.

 

You're talking about some very specific needs the cam has to meet. You're discussing how you will degree the cam, the custom exhaust you're using and the duration figures. You've even extrude honed your intake and you know your runner's effective length.

I couldn't make a more compelling case for a custom cam if I tried.

 

Just wondering if any of the custom cam grinders on this board want to take it on. I have emailed in the past with no responses. I have all the head flow information and I hope all the info that is needed. Thought I would give it another try. Maybe the XFI cam is good enough. Thanks in advance.

 

If you go with an XFI cam go with the 280 (230/236 .576/.571 113 LSA), there is a guy on TGO that passed smog with it in CA.

 

400hp is 500 at the crank…

Technically or actually? You can get lots of things past the actual test if you can get them to not look for the EO number, but technically you need to have EO numbers to be legal, and I doubt that you’ll find a healthy cam with one or your custom headers will have one.

That kills it right there. You’re not going to make 500bhp out of something before 6000rpm…, more likely you’ll have to rev it pretty close to 7000rpm to make that kind of hp out of 355cid.

12”??? The stock TPI setup is something along the lines of 25” total runner length and most carb manifolds are around 10”.

If the whole intake assembly flows 27xCFM/runner and you’re running similar flowing heads, yes, it is possible, but you’d have to rev it much higher then you’re considering.

 

California smog requires that the vehicle can hold 25mph and 60mph with no more than +/- 1mph at 50% load (I think those are the numbers, but you get the idea) that means that the cam has to be relatively mild with a 6 spd, with a stalled auto you may be able to get by with a little more "lump" but I am not a smog cam expert, and I have never tried to spec a cam to meet those parameters, I am having Bret Bauer do it for me. The 218 XFI cam was my "off the shelf" choice.

 

I have the receipt for SLP headers I bought in 1991. I have used it before to pass. The custom headers look the same from the outside. So technically for smog. Heck my custom cold air intake is illegal but no one has ever said a thing.

You are right about about 500 at the crank and that is why I want to know if it is doable. I don't plan on reving the motor past 6200 so as you say that might kill the deal. However on Dynosim which is not the real world it does show it to be doable. That is why I'm asking for opinions from the experts on the boards here who are very knowledgeable.

I do not have the stock TPI system by any means. I wish I knew how to post the pictures. The plenum is opened up more than anything I have seen. 1/3 of the SLP runners have been converted to plenum. The other 2/3's have been fully siamesed to the intake manifold. So in effect the plenum is extended to the intake. Effectually that takes away the runners. That leaves the heads and intake manifold for the runner length and the 12" that I came up with.

The Dart Pro 1 200cc heads have been flow checked to 276cfm at .600 lift and 264cfm at .500 lift before a little extra work. 2.050 intake valve. The head porter said after he was done that I could add an additonal 5cfm from .300 lift and up. Far as DynoSim is concerned I have stuck with the lower numbers. Exhaust with a pipe is 222cfm at .600, 216cfm at .500 and 193cfm at .400 lift.

I'll try to contact Bret again. I may have goofed the first time around. Thanks everyone.

 

You are limited to hp and rpm by the bigtube runners(slp, tpis, accel). Others have gotten close to 400rwhp on the thirdgen.org website, but only with much larger motors(400 cubes and up).

I don't know anything about dynosim, but it is way off on it's numbers. The stock and bigtube runners have a total runner length of 25 inches as mentioned, not 12.

Sorry to bust your bubble. If it weren't for the CA smog test and visual test you had to pass, you could hit your goal. The only smog-legal intake which will give you more rpm is the superram, but it is rpm limited on a 355 to about 6200 rpm, and that is with the intake fully ported and hogged out. My power peak on a 383 with the superram was 5500-5800.

The only real simulation program that I have seen that can let you change variables on a TPI motor is engine analyzer.

You have too many restrictions against you.

 

Here is a link to my plenum and runner modifications. The plenum is bored to accept my Holley 58mm throttle body. Just click on the links at the 1st, 2nd and 3rd posts to see what I'm talking about. You can see how I have enlarged the plenum volumn. I'm currently at 330RWHP and 370RWTQ with stock Trickflow heads and a very lazy ZZ9 cam and 9.9:1 compression. 212 on the intake and 224 on the exhaust. Just asking for 70 more RWHP.

http://www.thirdgen.org/techboard/tp...ml#post2216114

 

def. not positive about this or even sure if it would help but what about a modded lt1 intake? They flow well enough to handle a 400hp motor.

 

The problem with the LT1 manifold is it is not smog leagle. I have been able to pass smog with my modified TPI. I will get the manifold checked for flow when I do the motor swap out. If it needs more CFM I'll have it Extrude Honed one more time to open it up some more. Looking for around 275 cfm or a little higher to at least match the heads.

 

I spent a little time digging around thirdgen, looking at dyno graphs and pictures you posted there.... When you said “highly modified TPI. Effective runner length is about 12 inches” I was picturing something totally different, not to be a PITA, but you just have a siameesed TPI, which people have been doing for years and years. When it comes down to it you’ve ended up with something that still sort of acts like a TPI (even the siameesed runners will to some extent act as individual runners, just nowhere near as strong a signal/tuning effect), keeping the problems with the TPI intake and not really gaining much.

You still will be restricted to the worst choke point in the assembly, which is probably in the base somewhere, you will have the drag created by the long runners and especially all the turns the air has to make to go from section to section and you have the crappy intake to head entrance angle that will always restrict flow. Without extrude honing the final deal completely assembled I’d be shocked if you don’t have port to port inconsistencies and there is no way that the whole assembly flows anywhere near what even the worst part of it does. If you want accurate flow numbers you’d have to have it tested with the whole assembly bolted together from the TB to the heads, and then I wouldn’t be surprised if your actual cfm flow isn’t in the range of 20% under what the worst is for any of the individual parts.

Usually siameesed intakes gain a little WRT to peak hp, loose some wrt torque and don’t really significantly extend power band past where it would be with similar non cut parts, so in most cases the cars actually run slower unless other changes are made at the same time.

Don’t get me wrong… you’re making some nice numbers with it now, but I’m not sure that they’re anything that you couldn’t have done with similar parts or with an SR with a lot less cutting and grinding.

The point of all this is that you’re not going to make the power you’re wanting with that intake (at least not without sinking a lot more time and money into it) and not at all in the power band that you’re hoping to make it in.

Now if it was me, I’d start looking for other options. One thing that this setup really has going for it is that it is nowhere near stock looking and you’ve managed to shoehorn it through emissions anyway without proper paperwork. That being the case I would seriously consider what it would take to get a short runner like an MR or LT1 intake or even a HSR or converted single plane through. Maybe you can sell the MR/LT1 as a later model conversion, run the EGR externally like the LT1’s and vortec engines did. We’ve done all sorts of stuff to pass what used to be a rather stringent visual inspection, one of my favorites was fake bosses for emissions doohikies (like the EGR) that in real life go nowhere, just look right… Maybe late model ‘vette engine covers are a way to make all sorts of odd stuff look stock. Single plane EFI setups can be made to look stock with a big TBI style air cleaner on them…

 

Can't you just buy an inspection sticker in CA?

 

I think the SLP runners are smog legal, but the higher rpm tpi intakes are not. The only way I see him hitting 400rwhp is by going with a carb-legal single plane carbed intake(if there is one?) with injector bungs, throttle body and a fake egr valve as listed above.

The only other way is more cubes, meaning 400+ inches. Your making 340rwhp now, but the intake system is already maxed out. Unless you can put an LT1 intake with egr on the back on the car and convince them it was a complete motor swap? I don't know the rules on CA motor swaps.

There is also the First intake which looks just like the stock tpi but is larger, but I don't know if it is smog legal for CA.

 

Heh, I just boxed up a First setup for shipping 5 min ago…

I’ll be hard pressed to believe that any long tube setup reasonably close to the stock TPI layout will feed 500bhp…

There are no single plane CARB legal manifolds, which is why I suggested either trying to slide the LT1 in as an upgrade year wise or to hide a carb conversion manifold under a big air cleaner like it was a TBI…