Inliners International Forums General Discussion Engines No Additional Power After Carb and Intake Swap

Just got done putting on the new offy intake and holley 390cfm 4 barrel on my 250 and something seems wrong because I can't tell hardly any difference between my single barrel and my four barrel's performance. I'm pretty sure it's running rich because there's a bit of smoke coming out of the tailpipe. What jet sizes do you guys suggest for the primaries and for the secondaries? Would it running rich affect the performance this adversely?

You are running the stock type exhaust manifold & that is a big restriction, you have the intake breathing good, but now you need to open up the exhaust.

Plus the stock camshaft is anemic that holds back the engine as well.

It's all in the complete package,not one thing will make a huge difference when bolting onto a stock engine.


MBHD

Well does the 2.5" manifold count as an upgrade? Or would I need to fabricate some crazy header concoction for the turbo setup?

I understand that each part relies on each other but it seems like it would increase a LITTLE bit... I mean I remember reading some results from somewhere on here and it said the offy and 390 would give an extra 15hp so it seems like I would feel that.

But I do know that it is rich so how would I adjust that? Just get a kit and try and try and try? Or do you guys have a suggestion for a jet size?

The 2.5" manifold is an upgrade but not as good as a split manifold like Langdons http://stoveboltengineco.com/index.php/c...product=1395980

Or some headers will boost up the power.

But for a blow through turbo a 2.5" stock type manifold will be the easyist & a low dollar manifold to bolt on.

You will see an increase in power, but it will not be a day & night difference in just a intake & carb swap on a stock engine.

You would need to install a 2.5" ex. manifold, run 2.5" exhaust system & a cam swap to see a good difference in power.

Do you have a line on a 2.5" exhaust manifold yet?

MBHD

Well I asked Tom if he had any and IIRC, he said it would be $50 and shipping. I was really interested in it and almost bought it but tom never responded to one of my questions and then we both kinda forgot about it. But I just got this week's pay and can probably have more than enough by next week's pay. I just need to strike up the details with him.

I'm just curious as to why the headers would give better performance with the turbo setup. I mean isn't the 2.5" manifold the same thing I would do with the headers but already one piece? I mean if I got headers, all I would do is just run pipes together and make a flange off of them... So how would it be any different?

I lied. The swap actually managed to shave my 0-60 off 1.6 seconds... Now it's only 11.8 :-(... Aw well. I leaned it out some by raising the idle through the screw and leaning the idle screws so now it runs better but still seems a tad slow.

Changing your idle mixture will not improve your 0-60 times. Keep tuning.

I have since sold that 2.5" truck manifold.

To tune the 390 carb, the running mixture at cruise can be leaned up by changing the main jets to a smaller size. Many time after doing that the WOT mixture will be lean. This is corrected by opening up the PVCR holes with micro sized drill bits. Figure out the size of existing PVCR and then open it to the nize bit in the set. Do not just drill away with any bigger bit! This is something that is hard to reverse after doing.
What this does is lean up the mixture with jets but yet supply extra fuel thru the PVCR circuit to make up for the smaller jets.

Snowman,
since you are still normally aspirated, that is how I am speaking to you about modding your engine now,normally aspirated.

You can make decent power w/a stock 2.5" truck manifold for your turbo set-up.
You would make more power w/a SPA manifold or a tubular turbo manifold,all of which will cost more $$$.

Since I am still thinking you are on somewhat of a budget minded turbo build I am suggesting low dollar build parts.
To make the turbo mount more straight bolt on, I would suggest a SPA turbo manifold, but will cost you , as an example: http://cgi.ebay.com/ebaymotors/Spa-Turbo...sQ5fAccessories

So I must have thought you are talking about normally aspirated parts, that's why I answered the way I did.

I have said it before, you can make a lot of power w/a log type turbo manifold,you will make more all out power w/a equal length tubular turbo exhaust manifold

It all depends on how much money you want to spend & how fast do you want to go?

MBHD

I'm not saying that it was the idle mix that helped the 0-60 times. Just the intake and carb swap as a whole.

How are you checking your 0-60 MPH times?

I use a Belltronics FX2 meter, seems pretty accurate.

http://www.beltronics.com/manuals/gx2manualrev1.pdf


MBHD

Just a rudimentary way. Friend with a stopwatch who watches my speedo. It wasn't for a precise measurement. Just a general idea of how fast I'm going

You won't gain any power if the engine didn't need anymore air fuel. With out changing your driving style or internal engine parts, the original carb supplied all the engine required. I doubt adding headers will make much difference either. You need to change the engine as a whole, cam and air flow are the main two. You can add a carb twice as big if you want, but if the engine doesn't need it, its a wasted effert.

By definition, any engine originally equipped with a 1 or 2 bbl. was designed to run at 3.0" Hg. vacuum WOT, which means it's not getting enough air.
Not even factory race engines get all the engine needs, because the threshold for accurate venturi metering is higher than the point of zero pumping loss.

>> I leaned it out some by raising the idle through the screw and leaning the idle screws<<

raising the idle through the screw? What does that mean?

Did you set the float levels?
Did you adjust the mixture screws for highest vacuum?
Did you adjust the mixture screws for lean roll or what method did you use to adjust them?

there's that voodoo again!