87 intake manifold & plenum swap.
- Thread starter matt921
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I was wondering how the cylinder distribution is with these modified uppers. Are the back 2 cylinders still lean like with the stock upper, or is it completely different? Was going to run power plate with mine. I'll post pics of my modified upper soon. Does the standard power plate help it or has anyone sent a modified upper to RJC to see how it flows?
As far as a chip, will start off with my current chip, but will do some kind of upgrade. Looking at maybe the SD2 or maybe even the Dynamic EFI setup? Anyone here running it?
As far as a chip, will start off with my current chip, but will do some kind of upgrade. Looking at maybe the SD2 or maybe even the Dynamic EFI setup? Anyone here running it?
The volume of air into the intake is not changed by a properly modified upper plenum, so the RJC Power Plate should work the same.
At least that is my opinion, but I certainly have no numbers through the intake runners to back that up. I would yield to anyone who
does have runner flow numbers with flow at pressure through the intake - a tricky flow setup! It would require major fixturing
to flow this and prove anything. Just IMHO. The only flow that I know of that has been done was just the modified plenum vs.
the stock plenum on an otherwise stock 87 intake.
People claim an increase in boost psi after the powerplate, so wouldnt that mean it restricts air flow at least slightly, although may be still benefical since air distribution would be more even which is the purpose of the powerplate correct?
I was just wondering that since there is more than one configuration of powerplate depending on the intake or upper you're using(Hemco, etc), that maybe since these stock uppers are modified, that the power plate for the stock upper isn't the right one anymore. Probably better than not running one at all, but not optimized for our application now.
I was under the impression that the front two cylinders were the ones that went lean not the rear 2?
Nope, back two cyls are leaner. Airflow hits the back wall of stock upper and straight down into back 2. With the way we are modifying the stock uppers, it's probably worse, which is why I brought it up.
Also, I misspoke, there is no PP for the Hemco. There are for the Precision upper, BGC intake, KB, stock, etc.
Also, I misspoke, there is no PP for the Hemco. There are for the Precision upper, BGC intake, KB, stock, etc.
My guess would be that the Power Plate would be different, but I don't know and there is not enough of the
modified plenums out there to make RJC interested in developing one for this application, so it probably
will be one of those unanswered questions that we run into?
I emailed Jason yesterday and asked him about it. He said pretty much what was said here that there isn't a big enough market to justify spending at least 40-50 hrs of r&d to make a PP for us. He wouldn't even guess if the PP for stock uppers would help or hurt. The flow info is on his website, I believe. I know I saw it somewhere within the last week or so.
Chuck,
I sent an 87 intake, a stock 87 upper plenum and a modded upper plenum that I had done, to RJC and he flowed them on
his flow stand and found that the flow between the stock upper and the modded upper plenum were the same. He did not
do the flow for me through the intake runners and that why I can't comment on it. It sure would be nice to know and
I am sure he could do it, but .................
Mine is modded like Matt921's. I can't post the pics of mine because they're too big. If someone wants to resize them and post them for me, pm me an email address. I can't resize them on my phone to post them.
It would be nice to know how it flows from runner to runner.
It would be nice to know how it flows from runner to runner.
there is a thread on the the air flow using the power plates and a stock intake and plenum ...... It makes for a great read Myself and richard clark and flowed about a dozen different style intakes and plenums with various combos..
If you guys want to see how those modified plenums flow send one to me and i will flow it on a stock 86/87 lower and get some numbers...
I'm betting that it makes the rear two cylinders leaner and a stock plenum... But if oyu have alky injection it will feed more alcohol to the rear cylinders then to the front due to the alcohol droplets are carried by the air .... Thats what the thread is talking about in the link prost above by brent.
If you guys want to see how those modified plenums flow send one to me and i will flow it on a stock 86/87 lower and get some numbers...
I'm betting that it makes the rear two cylinders leaner and a stock plenum... But if oyu have alky injection it will feed more alcohol to the rear cylinders then to the front due to the alcohol droplets are carried by the air .... Thats what the thread is talking about in the link prost above by brent.
I've never had any issues with my modified plenum or with the leaning 5 and 6 cylinders out. But what I'm wondering is what kind of power can I put to my setup. Anyone have track times running an 87 intake and modified plenum swap? I daily drive mine and I would love to bring it to the track but before I do so I'm still working on getting it 100% healthy. Also I get about 16mpg city and 18-19 highway which is pretty awesome 
mattpere410
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- Sep 23, 2022
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Can you send me these pics?
