430-435 CHP now.....What can I do to get 500-510 CHP?

[XfireZ51]

Originally Posted by Vette73

So basically when I sent out my plenum and I/Hs I should have been aware of Siamese porting? I'm guessing this should have been done when I originally had my porting done?

Or, is this modification have to be done in stages, and to get the most out of it, should the secondaries be relieved?

Juuuuuust a little confused....

There's no "silver bullet" to this. You could make the case that u should have had the heads ported and cams installed too. I think most of us have "upgraded" power on a step by step basis. I know I have. It helps if u r the kind that likes to constantly tweak things.

[Vette73]

Originally Posted by XfireZ51

There's no "silver bullet" to this. You could make the case that u should have had the heads ported and cams installed too. I think most of us have "upgraded" power on a step by step basis. I know I have. It helps if u r the kind that likes to constantly tweak things.

Good point ....As far as pulling the heads for porting I know I could not have done that....If I go that route I would have someone do all the work...

[Paul Workman]

Point of fact, Pete's motor does not have siamesed plenum or IH and is making north of 474 rwhp, back maybe 5 years ago. (Has bigger cams now). But, on the other hand, the GEN-II LT5 has siamesed runners, a single injector per cylinder, and made close to 550 hp at the FW. (I guess one could conclude that removing the secondary port throttles appears to have some advantage, being it is supported by the latter design. I know I'd never return to the SPTs - even if I could.)

There is some serious engineering that goes into intake dimensions architecture, and being that such parts for the LT5 are not so abundant as to experiment with, for ME I'd rather do the math and/or follow the successes of others that be on the "bleeding edge" of a hot rodder.

[Top Toy]

Dom - considering the porting and other mods you've already completed, my best guess is you'd pick up another 10-15 RWHP with siamesing. My plenum and injector housings are completely siamesed all the way down to the heads.

Vette 73 - as Dom pointed out, many of us have made a sport out of continually tweaking our cars to get more out of them and benefit from each other's experiences. Siamesing may be the last thing many people do but it was the first thing I did to my otherwise stock engine and I could not have been happier with the results.

[LGAFF]

alot of factors in individual results; cam timing, etc. My 90 made 441 rwhp @ 7100 373 ftlbs @5300 with siamesed runners and ported heads, but the torque seemed alittle low and they were large ports. Given, the car was never professionally tuned....cams are smaller, now I have ported 93 runners on the car ported to 36MM+, would be curious to see the difference; last year ran 12.1@121MPH with an 800RPM launch and a tach that was way off...




My large plenum test resulted in a 20hp loss.



large plenum:
http://www.zr1.net/forum/showthread....hlight=siamese

[tpepmeie]

Originally Posted by Paul Workman

But, on the other hand, the GEN-II LT5 has siamesed runners, a single injector per cylinder, and made close to 550 hp at the FW.

One has to be very careful drawing a comparison to the Gen-III engine, which indeed did feature a single intake runner per cylinder. That manifold and intake port were designed from the outset as a single hole--it is not as wide side-to-side as two separate holes with a divider in between.

When one makes our design injector housings "Siamese", you are dramatically changing the cross-section area of the manifold runner. And it doesn't necessarily flow more than a properly ported 2-hole design. I have airflow data showing a ported 2-hole design approx. 36mm each outflowing a maxed out fully siamesed housing.

I am a believer in keeping the correct port velocity through the whole intake tract. Not everyone subscribes to that--a lot of "bigger is better" out there. That's ok, different courses for different horses, or however that saying goes.

[LGAFF]

Wanna flow test a bigass plenum?

[Johnny5]

Originally Posted by Paul Workman

You make an excellent point! As Miarc's web sit shows, you can get to "whatever" hp level you want a bit at a time as budget allows.

Maybe the best "bang for the buck" is porting the top-end: the plenum, the IH's, and port matching the heads (and a tune afterward, of course) and headers. You'll get 90+% of the performance increase one would expect after also doing the heads, for a fraction of the $$$. AND...ALL of it can be done w/o removing the motor. The next step in the evolution is porting the heads (at least). Because to do so is a "quantum leap" $$$$ wise, this point is characterized as "PHASE-I".

At this level the performance is transformed. My trap went from 113 mph to 118 mph without loosing a bit of dirveability or reliability in the process. And, honestly, if it were not for a burnt valve (probably due to the bad injector) I may have stayed at that level. But, since the motor had to come out to fix the valve, etc., I opted to finish my porting.

And, that said, although I picked up ~ 35 hp at the wheels for the effort (and $$), it wasn't the 'kick in the butt' I got from "PHASE-I"

Speed cost $$. So, get your wallet out for the next step.

The next "PHASE" (call it PHASE - II) i.e., porting the heads, involves removing the motor, the porting itself, re-phasing the cams, reinstalling the motor and then a live dyno tune...at a minimum.

At that point you'd be at your "510" goal. However, for far less than the incremental cost to port the heads, NOW would be the ideal time to install cams too! Cams more or less double the wheel hp you would expect from porting the heads alone. And, if the TB has not been opened to 63mm by now, doing so completes what all but the most intrepid modders would call PHASE II. Rear wheel (Dynojet) HP at this point will be around 450 SAE (where it matters). But, for bragging rights - dividing 450 by .82 to .85 will give you a nice chp number look at and show your friends.

As far as costs go, obviously the more of the work you can do yourself, the less out of pocket expense will be - not to mention the experience gained in the process!

In my mind, the next two phases (NA) are bore (sleeves, to be exact), and maybe off-set grinding the crank. The last phase is adding closed deck sleeves and a crank, tho the closed deck option could be done any time the motor is out for whatever reason, $$$ provided, of course.

Those boys that have done "the whole 9 yards" (427 or 441s) can attest to the raw snap of the neck one gets from going all the way. But, it ain't for those with thin wallets, fer sher!!

Ok, I don't really follow. My understanding is that porting the heads is porting the heads, its only called port matching if you ported the plenum and IHs. Aren't you just making the air holes larger on the heads? Why are some people saying you can port with motor in and do a full porting with the heads out??

[Vette73]

Originally Posted by Johnny5

Ok, I don't really follow. My understanding is that porting the heads is porting the heads, its only called port matching if you ported the plenum and IHs. Aren't you just making the air holes larger on the heads? Why are some people saying you can port with motor in and do a full porting with the heads out??

What's up Johnny?

Yeah I hear Ya......With my backyard mechanic skills I'm a little confused also about portong with motor in and porting with motor out...

From what I inderstand is to port the more " important " part of the head, the motor has to come out....With that I say, with the motor in and doing whatever porting you can, how much horsepower and breathability will I pick up? 20-25 RWHP?

Hey, maybe that's good enough without having to pull the motor, am I right?

I think I see Evolutions point about pulling the motor because you have access to the cams at that point.......

End result is- how much are you willing to spend to get more useable power? That's the question....

Or, you can just pick up a C5 Z06 with a head and cam package, and if your lucky enough a supercharger and be done with it...Lol..

Peace ...

[We Gone]

My understanding of why pull the motor to do the heads is in a nut shell, Its a lot easier to remove the heads and everything that has to come off. Upon reinstall parts it makes timing the cams much easier. The plus is you can do a better job cleaning the engine and engine bay.