ZR1Pete

I put the siamesed plenum on my 350 LT5 took it to the dyno and got zero gains withen the 1% tolerance.
Lost nothing in the low end i printed one of my old dyno pulls with one of the new ones and the lines are almost on top of each other.
I even took 4 inches of runner out with no change in driveabality the car drove the same i can't tell a differance.
Still looking to crack the 450rwhp mark in a 350 c.i. LT5.

Bigger isn't better.

On to the next mod.


[Modified by ZR1Pete, 9:08 AM 1/15/2004]

USAZR1

Maybe you can explain why David Haag's LT5 went from 395rwhp to 422rwhp and torque from 340rwtq to 369twtq,,with nothing more than a Jeal siamese plenum & Van Deventer siamese injector housings. Other than a chip recal,I didn't make any other mods to the engine.
"Bigger isn't always better" might be true for your engine but let's not make that a blanket statement. Every engine responds differently to various mods.

MrCrowley

I would have to say that Davids plenum is no where near ported like Pete's original one. Pete has the produced the most power out of a 350cid to date. He went very big on his ports on the plenum, ih's, and heads. Maybe Davids ports were larger on his heads than his plenum. There are alot of reasons why his improved so much. But in Petes case the siamesed plenum, and ih's actually match his heads, but the plenum will outflow his heads. You have to remember that Pete made 436rwhp, which is a good bit more than David. And it will take a few tries to figure out what will give him more hp.

Now with that in mind I would say Pete needs more cubic inches, or more Cam to support the extra airflow. Bigger valves may also help, but that is what R+D is all about. Al is also assemblying his 415 as we speak, and he will try the siamesed plenum and ih's on his setup, and compare those to his own intake. I will be curious to see that, as a 415 is 20% more cubic inches than a 350. And with that in mind it will probably need the extra airflow.

One might think we would loose power. That isnt the case here! It remained the same which is a good thing. Even with the divider removed 2inches down into the ih's. We are in the right direction of finding the hp, we just need to uncover the blanket to get it!

Mike






[Modified by MrCrowley, 12:29 PM 1/15/2004]

BERTZR1

I don't think it's A blanket statement David Haag's plenum and IH probably
didn't flow as well as Pete's before going to the siamesed set up.Where as Pete's are maxed out already on A 350 cid lt5.


We'll keep trying.

:chevy :chevy

90 Corvette ZR-1

I always heard that on a stock displacment LT5 a siamesed plenum will not help that much, if at all. Maybe I heard wrong though.

DDSLT5

I think that the bottle neck is the valves now, not the inj. housings or plenum. I think he could make more hp with the bigger valves, but I think his torque is maxed out. Need more cubes for more torque. :seeya

ZR1Pete

Clint your right,i didn't mean to blanket the siamesed intake results i guess i should have said what the results were for my car only.

I was basing my hopes on your results and was hoping if i can at least see half of what you have gotten out of the siamesed plenum i'd be satisfied.

There's a couple of reasons i can think of why you gained close to 30rwhp and raised your peak RPM's, one is what Mr.Crowley and BertZR1 wrote and second is you have performance intake cams,i think the stock ported plenum wasn't enough for that cam.
I have stock cams.
I think the restriction i have now is at the valves and cams.
I will bet there's another 15-25 RWHP out of your old/David's ZR-1 if the heads were only extrude honed. Just send me your heads.
Clint if possible can you e-mail or post the specs of the intake cams in David's ZR-1 or who can i call to find out.

Again,the idea/decision for me to try the siamesed plenum was when i found out you made an extra 30rwhp i would've been satisfied with half that.

I might try bigger valves next, depending on finances anybody wanna donate some $$$ for R&D :D :D

A26B

I have a GREAT idea :D Why don't you just sell me that 'ol siamesed plenum. Even though it's been modified I'll still give you a couple of hundred bucks for it! Should I hold my breath? :lol: :lol:

The Lurker

First of all, stock heads only flow 265 CFM at 28" of water. To get the maximum out of our 350 you need to flow around 303 CFM at 28". Of course, this is all dependent on cam profiles so it gets a bit messy figuring it all out. The upshot of this is if your heads don't flow what you need it doesn't make 2 cents what you do upstream. also, I have said this forever here, a huge bottleneck in our system is in the injector housings. Bolt on the injector housings and you will see a 15 cfm drop on the flow bench. Porting most certainly helps but to really remove the bottleneck you have to weld up the housings in several spots and reprofile the airstream. The plenum is not a huge deal in the overall scheme of things.

MrCrowley

All that was done to the Injector housings to match his heads and plenum. Here is a pic of one before polishing. The plenum does have more volume due to the siamesing. And the IH's have the divider removed about 2 inches down, to create the velocity needed to enter each valve port. With all that in mind, I would have to say the valve and seat combination is the next issue on hand.






[Modified by MrCrowley, 6:07 PM 1/15/2004]

sultan

dear sir are you comaparing a dunn head LT5 to non Dunn heads like pre 1993 , cos i read some were that if the LT5 93 and later heads it has the best packige for the 350CI
:cheers:

GTB/ZR-1

Put that on a big-inch motor and I believe the results may be a little different ;)
Nice looking piece, who & how much?(edit: I just realized that's MrCrowley's work) :thumbs:


[Modified by GTB/ZR-1, 11:19 PM 1/15/2004]

USAZR1

Mike,the LT5 is my former wasn't all that radical. Guess that's why the hp & tq increases with the new plenum & injector housings were so surprising. Before the new parts,the top end (heads,injector housings,and plenum) were ExtrudeHoned,the throttle body was a Van Deventer 63mm,and the cams were Jeal 422's. Headers were 2" Jeal. I dynoed the car at BG on a hot,humid day and its numbers then were 395rwhp and 335rwtq. Those numbers were a disappointment because it had dynoed earlier that year at 392rqhp/340rwtq with the old top end. However,the A/F ratio never climbed above 11.1 so it was obvious a serious leaning out would really help. After I sold the car to David,he had Corey Henderson do some chip recalibration and the new numbers read 422rwhp and 370rwtq. If it had been someone other than Corey,I probably would have been pretty skeptical of the results.
Bottom line: the only change was the Jeal siamese plenum built for a small displacement LT5 and a pair of Greg Van Deventer siamese injector housings.
Before those parts were added,the A/F ratios were right around 12.8 so the engine was in a good state of tune beforehand. OK,if the siamese injector housings & plenum didn't add the power & torque,,what did?
I have no reasons to fudge the numbers. If they were a waste of time & money,I would say so as those parts were not cheap and would hate to see someone else make the same mistakes.

David Haag

I believe cams are what Pete needs to get to the next level. If you beef up the valves you might as well go all the way. Thats alot of money. I myself have decided to go to a 402 stroker. Corey is gonna build it and we will use stock valves with very aggresive porting and big cams. Pete, I might be selling my jeal intakes if you are interested. Your setup will benefit the most with these bigger intake cams. I will keep you and everyone else posted to when I am ready or should I say when Corey is ready.

The Lurker

We found generally, even for the big inch motors, taking the bifucation down into the injector housing is more detrimental than any benefit derrived. There is a loss of low end without any appreciable increase in top end. Keeping the bifucation there at the top allows you to maintain power at the lower levels and that reflects in the overall upper end power as you don't have to make that up as the power increases. Basically, you hit max power sooner keeping more power underneath the curve.

An option here is to remove most of the metal and "D" port the runner with a thin piece if aluminum welded and blended into the runner. This does cause a turbulance with the imbalance of air pressure but in a runner turbulance is not bad, just that it is not a balanced turbalance. This may cause a tumble into the cumbustion chamber and the debate over tumble versus swirl is still not answered.

That just my opinion, I could be wrong. Whatever floats your boat is the right answer.

BTW Mr. Crowley, very nice work. Two thumbs up.

MrCrowley

Thanks! I am eagerly waiting for Al's(415) results too. I am pretty sure he will dyno twice. Once with his original plenum, and then with the siamesed setup I made for Pete. Btw........Thanks Pete for the long awaited dyno results!

ZR1Pete

I would do it all over again.
Mike,you deserve a big thank you for all the hard work you did.

Rkreigh

very interesting stuff. Lurker, do you know if Bill has been able to dyno the new intake??? I'm very interested in seeing if these will make production and be available. with some good cams/heads, I believe this intake will really pick up the top end power.

even though it's a big expense, if you have a 4" bore motor and especially a stroker, I think the bigger valves are worth it. my little 390 makes 505 rwhp with the 239 cams and the bigger valves, and I agree that changing the intake "may" not help, but I would like to try it.

the Billy K intake looks pretty radical and I sure would like to see how it does. it has a very straight shot from an oversize plenum which should really flow well in comparison to the kink in the stock injector housing.

thanks for any thoughts.

David Haag

A good comparison for Rons car would be Bob Halls. His LPE 385 made 513rwhp with a siamesed plenum and big valves. So we have a 8rwhp gain. Corey H just did a ported a plenum and inj housings on a stock lt5 with jeal headers and a corsa exhaust no cats. The car made 400rwhp. Its a yellow Z license ZR1FUN.

The Lurker

Yeah, I think that was Cory's first shot. He called me and talked about it. I told him not to be afraid to let loose and make those things work. He did a great job.