blowthrough carb and cam

[1967JMG]

Sorry if this is a reoccurring kind of thing on here. It's just there is such a wealth of info on the topic all over the place, i thought i would see if i could get some good info on it in one thread.

I want to build my 200 to add an m90 in the future, possibly way in the future...
my thought is 8.9:1 compression 274-110 cam, AL head and intake.

So, i've seen alot of people are using demon carbs, holley 390's, etc... What would be the best carb to use on this set up till I can add the supercharger? And which one would be easiest to adapt to the blow through design? I want to run 7 boost.

Next, How would that set up run before the charger? The C/R will be a little low for the 274-110 cam. How would a 264-110 or 112 work with 8.9:1 and 7 boost? would those cams be too small? I dont want to go too overboard, This is still my daily driver...

JMG

 

[rbohm]

8) the holley 390 is a good carb to run even with a supercharger on these little sixes.

 

[Broncitis]

I'm not sure about the carb for this application, but I can shed some light on the cam and C/R, make no doubt about it my loyalty to mike, but for a cam for this application I recomend a custom ground cam, I would love to see someone run the grind I have from bullet cams, its posted under check this out under al head page 1, check out the timing events, I thought they were crazy until I fired this thing up, I would love to see it in a stang, I think 13's would be easy. Now back to the C/R, if you zero deck the block and the al head runs true to 56cc's as mine did, you will have 8.9-1 with dished pistons and be able to run premium gas with 7 to 8 psi. To obtain this you will need to run an 8.75 dampner pulley with about a 3.4 blower pulley, an oval port m90 may take a 3.2 or 3.3 pulley to get to 7 lbs. One side note, even though I spun rod bearing #6, the cast pistons and rings were in perfect shape with boost, PM me if you want to talk further.

 

[Broncitis]

One more thing, over the counter, the 264/274- 112 will work best in my ponion, the M90 profile will be different than a turbo, no exhaust restriction. A turbo is more efficient than the m90, but stop light to stop light, both without stall converters, you figure it out, I won't open that can. One of the reasons the guys with these hot 2.3 and 2.5 motors run turbos, is a positive dispacement blower causes to much parasitic loss with the small dispacement, thats why I think the m90 was made for the 250 and I'm starting to build one even though I have nothing to put it in at the moment, build it and a car will come,its my lie, let me tell it.

 

[Anlushac11]

Get a turbo cam. The engine doesnt care if its draw through or blow through. It just knows there is pressure in the intake tract.

You would build the engine the same if it is a draw through or a blow through setup.

I would go with a Holley carb just for ease of finding parts, and you will need to switch to solid floats and a boost referenced fuel pump.

Or you could go with what someone else here is trying and add a Ford 350CFM CFI setup or a GM's TBI fuel injection. Then you dont have floats or power valves. You would need a fuel injection computer system similar to Megasquirt to control it all.

 

[Broncitis]

Are you suggesting a turbo cam for the M90.

 

[Broncitis]

Also if you read about the M90 you will learn that draw through is highly discouraged by the manufacturer.

 

[1967JMG]

I kind of understand about the turbo cam. I know CI says that the 274-112 is a great cam if one is planning on going turbo.
The thing is, I would be adding the supercharger, M90, at a later date. And like I said, this is my daily driver, so, I need a cam that will help me function as such, but still allow room to expand on. With having only 8.9:1 C/R for possibly months before installing the M90, i think it would be a bear to drive with a 274-112 cam. That is why I was looking at the 274-110 that way i could maintain some of the bottom end power. Although if I went with the 264/274-112, isn't that cam rated for the same RPM range as the 274-110? Though, I guess still having the 264 on the intake side would still help keep the bottom end before adding the boost, correct? and the 274 exh and 112 LC would help with the top end...?

That brings me to this, and please correct me on this if I'm wrong. As far as the dual pattern cams, I'm still not sure if I completely understand the full benefits of them. I would think that the exhaust is only going to put out as much as it can intake. So would having more exhaust duration make up for the size difference in the intake and exhaust valves? I would imagine that doing that would give more power because the motor would be able to breath out more of that air it is sucking in... right?

 

[1967JMG]

Anyway, still as far as carbs go, I know holley is probably the easiest to get parts for. What parts of the carb would I have to change to make it ready for a blowthrough application? Can I buy a carb already made for blowthrough applications and not have boost going through it for a little while without suffering from any problems?

 

[Broncitis]

http://img166.imageshack.us/i/1000026rj6.jpg/

 

[Broncitis]

Well I finally figured it out how to post that cam profile, all I can say is I have this cam in the 200 in the bronco and it runs great with multiport fuel injection without the blower, I have no idea the difference would be with a carb with its timing events, all I know is with boost, this cam runs beyond my expectations of what I ever thought I would have for power, then again I believe the AL head is ideal for multiport injection, if I can do it, anybody can, once you learn your system, it gets easier and easier, but it was very difficult for me in the beginning, because I'm an electronics idiot.

 

[1967JMG]

what is the cfm of your set up? My concern when it comes to this is that i want to find something also that would be good for an NA set up that can be converted. Say I had a 650 cfm set up, if an M90 can increase the VE to as much as 120% thats really 780 cfm. How much is too much? if there is such a thing...

 

[1967JMG]

oh, has anybody on here ever experimented with the holley pro-jection set ups?

 

[Broncitis]

The set up claims about 670 cfm through the GM TBI converted to TB, in my opinion this is the easiest, cheapest, most plentiful TB or TBI you can have if you wish, injectors, IAC, and TPS all included, especially if you are smart enough to do a megasquirt set up to run it, I feel it can handle all you can blow through it for a 200 if you upgrade the injectors for boost.

 

[Anlushac11]

Just a thought...

You can also adapt the head for direct port injection and use the GM TBI unit as your throttle body and sensor pack.

IIRC there are two main GM TBI's. The smaller one is about 480cfm IIRC and came off V6's and small V8's.

The other is around 670cfm and came on GM 454 V8 trucks.

 

[65ShelbyClone]

Anyway, still as far as carbs go, I know holley is probably the easiest to get parts for. What parts of the carb would I have to change to make it ready for a blowthrough application? Can I buy a carb already made for blowthrough applications and not have boost going through it for a little while without suffering from any problems?

There are a number of walkthroughs online like for modifying Holley carbs to be used with blowthrough turbos and blowers. This is a popular one:
http://www.hangar18fabrication.com/blowthru.html

what is the cfm of your set up? My concern when it comes to this is that i want to find something also that would be good for an NA set up that can be converted. Say I had a 650 cfm set up, if an M90 can increase the VE to as much as 120% thats really 780 cfm. How much is too much? if there is such a thing...

Carb size is not determined the same way for blowthrough setups as they are for NA/drawthough. As a blowthrough, even a 750cfm carb can feed over 1500hp. I don't think a 390cfm Holley would have any trouble fueling a 400bhp engine.

One more thing, forced induction does not increase an engine's volumetric efficiency. Mass air flow, yes, but if you have an engine with 75% VE and supercharge it, it will still have an actual VE of 75%. The only difference is that the intake air density increased.