4 bolt housing AR size

[forcefed3.8's]

I am switching to a 4 bolt 7675 with my new set up. The engine is a 274" on center Stage 2 with 9.5:1 compression. I am running a 224 roller ( might be changing) and fully ported GN1's. Most likely I will go BB. Looking for opinions on the .81 or .96 AR exhaust housing.

 

[forcefed3.8's]

no opinions?

 

[Reggie West]

I would go with the .96 housing. It does depend what you are using the car for. You did not state what stall converter you are using but I would go with a 3800 stall speed non lock Art Carr or PTC. From what I have seen Dusty is really good at getting the stall speeds just right.

The .96 housing will need the higher stall speed to get moving down low but will flow well on the top end. The cool thing with a BB turbo is they build boost right at the stall speed of the converter.

Whomever you are buying the turbo from, check and see if they have a housing somewhere in between .81 and .96. I don't know if they do, but it never hurts to ask.

 

[Alky V6]

i would go with the .96 housing. It does depend what you are using the car for. You did not state what stall converter you are using but i would go with a 3800 stall speed non lock art carr or ptc. From what i have seen dusty is really good at getting the stall speeds just right.

The .96 housing will need the higher stall speed to get moving down low but will flow well on the top end. The cool thing with a bb turbo is they build boost right at the stall speed of the converter.

Whomever you are buying the turbo from, check and see if they have a housing somewhere in between .81 and .96. I don't know if they do, but it never hurts to ask.

x2

 

[forcefed3.8's]

I have an 18 blade PTC. The turbo will be from Precision. I think they only have .81 and .96.

 

[TurboBob]

I ran a .81 on my 274" engine. I think it was a good fit.

Bob

 

[forcefed3.8's]

The car is a street car, but I lived with a 76HPQ .85AR on a 245" engine with a 0 pump Vigilante.

 

[Alky V6]

My kid fought me on my suggestion of going with a larger a/r when he was ready to order his turbo. He ended up ordering the larger a/r and installing it. He was never happy with it even though the dyno numbers were respectable. He ordered the smaller housing to try it. He was convinced the smaller housing would be best. He installed it and we dynoed it. He lost power and spoolup was rediculously quick. Without any input from me, he put the larger a/r housing back on the car.
You're running a lot of cubes and good heads. Let the engine breathe.

 

[forcefed3.8's]

What turbo, how much power, how much boost?
At the moment, I won't be maxing it out. I am building the shortblock to handle whatever I can throw at it. I have alot of building up to do to the car to be able to handle the power. I would like to have the car go easy low 9's.

 

[Reggie West]

When you get to bigger turbos and a car that can run 9s you end up having to make some sacrifices. Either you have a street car that is very responsive down low and will be more power than you can ever fully use or you have a strip car primarily, that will flow on the top end and do the job no sweat. You can drive it on the street but it will be a little slow off of a light and come on lime gangbusters once it gets moving.

On the drag strip there are 2 rules. Leave under full power, cross the finish line under full power. A .81 housing may not let you do that, a .96 will. The 224 cam will make max power around 4400 rpms. You are effectively moving max torque upnthe rpm range from stock, which is why you want a higher stall speed converter to don the same. It's about the right combination between the housing on the turbo and the converter.

 

[bison]

If you're looking for 8 sec power I'd run the .96. If you only want low 9 sec power the .81 would be fine. I doubt it will matter much till you are over 850hp

 

[GNXTACY]

If you're looking for 8 sec power I'd run the .96. If you only want low 9 sec power the .81 would be fine. I doubt it will matter much till you are over 850hp

Bison at 3400lbs how much power do you think is needed (rwhp) to run low 9's?

 

[bison]

Bison at 3400lbs how much power do you think is needed (rwhp) to run low 9's?

720 to run 9.40. 800 to run 9.00. I was talking flywheel in my prior post.

 

[Alky V6]

720 to run 9.40. 800 to run 9.00. I was talking flywheel in my prior post.

That's an average hp figure for the run, right?

 

[bison]

That's an average hp figure for the run, right?

It's a rough number. The engines typically stay within a few hundred rpm of peak power through most of the run if the combo is right. If not the mph will still be there if the converter slip isnt bad but the e.t. Will be off. Especially through the 330'

 

[Robert Wilson]

I have a similar combo and I am using the .96 AR journal bearing 76GTS. Dynoed 743 RWHP with pump gas and alcohol.

 

[slimtastic]

i dont see alot of difference between a .81 and a .96. id bet either will make hp within 2% of eachother

 

[bison]

The 224 cam will make max power around 4400 rpms. You are effectively moving max torque upnthe rpm range from stock, which is why you want a higher stall speed converter to don the same. It's about the right combination between the housing on the turbo and the converter.

i have to disagree with this. Based on what Ive seen even versions of the 224 cam with even less intake duration peaked over 5300. Usually around 5400-5500 even when a lot of backpressure was present. On a 9.0:1 274 ci with a tangential housing and gtq ex wheel it peaked around 5600-5700 and didn't drop off much till over 6100. With a converter that flashed to 5500 the car was a bullet and not hard to gear since it stayed very close to peak power even 500 rpm over the peak rpm. This is when run with hyd lifters too. With solid lifters there is probably a couple hundred more rpm there. If you have enough power to run 140+ you aren't peaking at 4400.

 

[GNDriven]

Is there a difference in the rating of the precision standard style exhaust housing and the garret style? Like the 4276? I see these being advertised starting at 1.00 and going up. I think the most popular being the 1.28. This might be the difference between divided and undivided. .

Anyway I got a 1.3 A/R divided with the large 5" inlet compressor cover. Do you think I am going to be a pig off the light? My specs are very similar to thread author.

 

[SuperCPA]

Subscribing because I am in a similar boat with my 249 TA engine. I am looking in to replacing the older tech journal PT76GTS .81 with the newer 7675 CEA BB as well. Like you, I also have the 224/224 solid roller and a PTC stalled by Dusty. How much better is the spool up by comparison of these two with the same A/R?