Stock Crank\2.95 blower\PSI?

[brad87gt]

I just installed my t-trim a few days ago and was wondering if anyone else is running a 2.95 blower pulley and a stock crank pulley that comes in the kit. I am only seeing about 9-10 psi at 6000 rpm on my 306. It has stock Victor Jr. heads a ported Systemax II and a 70 mm t-body. I was expecting at least 12 -14. Is 9-10 normal for this pulley combo or do i have another problem like belt tension or something? The belt seems very tight though. Please let me know your boost levels with these pulleys.

[regattacoupe]

whats your elevation? powerpipe? maf size? I would think that 9-10 sounds low.

[MeJay Racing]

Sounds low to me also. Every combo is different but I would think you should be at least 12#s.

[s-trimmed302]

Brad,

Thats the exact same pulley combo that I ran first off with my S-Trim and I only saw around 9-10#...I was expecting about 13 with that combo but it just wasn't gonna happen..The Combo I run now, 8" Crank and 2.95 Blower, most people say that they would see around 18# but I only see 12-13..Go figure....Every combo Flows differently..

Jeff

[regattacoupe]

What cam are you running?

[s-trimmed302]

Brent,

Im running a Custom Grind from Ed Curtis..With my old cam I use to see about the same boost #s..

Jeff

[frdfandc]

Sounds to me like you have belt slippage. When my first engine was running, I was seeing 10 lbs of boost at 4300 rpm. Here was the combo and the failure.

Stock engine with b-303 cam and 1.7 rr's. 70mm T-body, s-trim with 8 inch crank and 3.15 blower pulley and power pipe.

The main reason I was only seeing 10 lbs of boost at 4300 is that the valve springs were shot in the stock heads, only allowing the car to rev to 4500 rpm. If the valve springs were good, I would have seen around 14-15 psi with stock stuff.

[brad87gt]

i have a pro-m 80 and an f-303 cam. I am at about 1500 ft. I want to run an 8 inch crank also but i was wondering who makes an 8 inch crank with a stock acc. pulley instead of the underdrive? Once i install the 8 inch crank pulley i will get a larger blower pulley if it produces to much boost for my stock block. In the spring time though a cog drive will be in place on an r-302 317incher that is being built. I would think it was a little low also but the guys at vortech said the 2.95 pulley is meant for 12-13 on a typically modified engine after telling the guys at vortech my head and intake combo they said it was normal at 9-10 psi.

[s-trimmed302]

Darin,

I dont have belt slippage at all..With an 8" Crank pulley and 2.95 blower pulley and a Semi tight belt I dont see any be,t slippage..I do have my Belt pretty tight and its not slipping.No belt dust at all..

Jeff

[frdfandc]

Usually belt slippage occurs at high rpms - 5000 and above. Its hard to watch the boost guage and drive at the same time. Have you had the car on a dyno at all? If not, you might be able to find a reason for low boost with that combo on a dyno.

[Racer LX]

We've run into that kind of thing before with the T-trim, had a stock crank pulley and a 10 rib 2.95 and still only saw about 10#'s of boost. Was told because the T-trim just plain moves a larger volume of air it's 'harder to turn' that blower at higher revs, and your belts and tension have to be really good with no slippage to make boost. I can see the logic there, though I'm not sure if that's 100% the reason our boost was low. In the end, an 8" crank pulley solved our trouble. With a 2.95" blower pulley we made 15#s of boost on a stock block 302 H/C/I motor.

What kind of belt are you using? Is it brand new, or older and already has gone through it's belt stretching phase of life? Do you see belt dust anywhere under the hood? Doesn't sound like you've dynoed with it yet, but if you see 'waves' in the power line at the top of the revs (like maybe 5000 rpm and up), that's what belt slippage can look like on a dyno graph. You can bead blast your pulleys for additional grip if you slipping, or maybe try a Reichart pulley? Just throwing out some ideas.

Hope this helps,
Jim

[MeJay Racing]

Sounds to me like you have belt slippage. When my first engine was running, I was seeing 10 lbs of boost at 4300 rpm. Here was the combo and the failure.

Stock engine with b-303 cam and 1.7 rr's. 70mm T-body, s-trim with 8 inch crank and 3.15 blower pulley and power pipe.

The main reason I was only seeing 10 lbs of boost at 4300 is that the valve springs were shot in the stock heads, only allowing the car to rev to 4500 rpm. If the valve springs were good, I would have seen around 14-15 psi with stock stuff.

Interesting as this weekend I was seeing 15#s on a totally stock 180k+ mile long block. Didn't even change the rockers. Only changes were 30# injectors, pro-m 77 and full exhaust. But it pulled all the way to my 5500 shift point. The only problem with going higher was the lack of a good ignition and blowing out the spark. This was with a 72 tooth crank pulley and a 29 tooth blower pulley. Not arguing. Just comparing combos. For what it's worth it did go 12.76 @ 109.55 @ a mile high (ABQ, NM).
Mike

[s-trimmed302]

Darin,

Yes I have had the Car on the Dyno and had it tuned also May 3rd or last year..I was then running a Stock 6.87 Crank pulley, and a 2.75" Blower pulley..Made around 11-12# of boost and I couldnt tighten the belt tight enough to keep it from slipping above 5500 rpms..This past winter, I made some modifications like a Custom Cam swap including Stiffer Valve springs, 1 3/4" Headers (from 1 5/8"), Custom 3" Exhaust with X pipe, 8" Crank pulley,2.95 Blower pulley, and Ditched my FMU..Im not sure where Im at now with these new Mods but it feels ALOT better than it did right after I got the car tuned...After I swapped to the Renegade BLower pulley Configuration, all Belt slip is gone..You dont have to Tighten the belt Nearly as tight with the 8" crank as I did with the smaller 6.87 Crank pulley....

Jim,

My belt is a Brand new Goodyear Gatorback 56.5"er..Its probably seen about 2000-2500 miles now..My belt is not Slipping and There is no belt dust under the hood anywhere..I know exactly what your talking about, about the Waves in the Dyno sheet caused by the Belt slipping..Had this done on the Dyno last year because the belt was slipping...BTW, my Blower pulley is bead blasted for extra belt traction! :)

[brad87gt]

where can i get an crank pulley with an 8'' 8 rib blower pulley and a stock size accessory pulley, not an underdrive? I see no dust under my hood at all either and i recently taken a passenger along to watch the boost guage and it appeared that their was no slippage just 9.5 psi from about 5500 to 6100 rpm. I would like to produce about 15 psi. I do not want an underdrive accessory pulley though, every 8'' blower/acc. puleey has been underdrive though? Does anyone make them without the underdrive?

[MoDo]

with my big heads, cam, and 331 i see 14 lbs with a stock (6.87") crank pulley and a reichard racing 2.95" pulley


if the belt is tight you might want to look at the bypass, i have seen them leak before


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