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I have been reading (for years) about how the swirl port TBI heads will destroy TPI performance. Seems like everyone agrees that it's a mismatch of parts. While this is not something I set out to do, here is the story.
Have a friend (dave) that bought a 91 vert (305tbi/T-5). This car was originally owned by the older guy fron Horsepower TV. Not sure of his name but there was only two host. He was the one with grey hair. Dave bought the car with headers and an intake IIRC. This was actually done on HPTV.
Dave installed nitrous and ran about 13.1 @ 105. I think it ran 14.9 on the motor. Very good times for a stock 305 tbi! Then he decided to modify the engine. Ported heads, long tube headers, cam and a few other things. Half way through the porting, he changed his mind.
I ended up building a MPFI 406 sbc for the vert.
....that is a whole other story though. Dave felt bad and gave me the heads. I bought the stock 305 from him also. My T/A had about 180,000 miles on it at the time.
Used the TBI shortblock in my 86 t/a for about 100,000 miles. Ran stronger than the worn out original. Then it started to have massive blowby. I pulled it apart and found some cracked rings. One of the piston ringlands was broke too (between the 2nd and oil rings). Bearings still looked brand new.
The bottom line is that my Trans Am runs very good with TBI heads. I have raced a bunch of cars and the 305 holds it own. Stock 350 TPI cars cannot keep up. 4.6l mustangs tend to lose alot. Gateway International Raceway will be open in a few months. Plan to have the nitrous setup by then. Hope some of you non-swirl port SBCs are out there. Maybe we can line em up!
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Last edited by 11sORbust; 11-25-2007 at 12:45 PM.
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Re: TPI 305 with swirl port TBI heads *Myth BUSTED!
I have ported and planed swirl ports on my L98. It has tons of low end torque. It's hard to keep the tires from spinning. Pulls hard to 4K or so, then it pretty much runs out of wind. It's fine for my purposes with an auto. If it was a stick I wouldn't be as content with it.
Re: TPI 305 with swirl port TBI heads *Myth BUSTED!
how exactly are you running such a big cam on those heads? i could be wrong but i didnt think those lt1's would handle the lift of the cam that youre running. and not to burst your bubble or anything but youre also comparing apples to oranges now. youre comparing stock 350tpi's vs a cammed 305.
also a stock LO3 your buddy had running 14.9 im not too into. unless the 5 speed makes a huge difference something in that car had to have been touched. i ran a 15.9 with a stock 305 TBI with headers, catback, gutted cat, no emissions, open element, 308 posi which that has i assume.
not trying to put you down because i too am going to be porting my 187 heads and camming my 305 and converting to tpi over winter, but i read your cam specs and unless you have special retainers or milled the guides down i dont see that working with 0.5-- lift.
Re: TPI 305 with swirl port TBI heads *Myth BUSTED!
Quote:
Originally Posted by vipershark11
how exactly are you running such a big cam on those heads? i could be wrong but i didnt think those lt1's would handle the lift of the cam that youre running. and not to burst your bubble or anything but youre also comparing apples to oranges now. youre comparing stock 350tpi's vs a cammed 305.
also a stock LO3 your buddy had running 14.9 im not too into. unless the 5 speed makes a huge difference something in that car had to have been touched. i ran a 15.9 with a stock 305 TBI with headers, catback, gutted cat, no emissions, open element, 308 posi which that has i assume.
not trying to put you down because i too am going to be porting my 187 heads and camming my 305 and converting to tpi over winter, but i read your cam specs and unless you have special retainers or milled the guides down i dont see that working with 0.5-- lift.
Yeah, it's kind of not fair.....racing a stock 350 tpi car. The 350 car I raced was not exactly stock though. He had headers, vig converter, tuning and a couple of other small mods. My car has the stock converter AND 2.73's!
Dave might not of ran 14.9 . Maybe it was 15.3 or so. I can't remember exactly. Do know it ran LOW 13's on a 100 shot. Keep in mind that a manual can perform better at the track. Take the best tq converter made and I bet your car would of dropped a few 10ths, easy. The stick has the ability to "stall" at any speed...
The retainers are stock LT1. They was just milled down
.050" for clearance. The springs are less than ideal. Yet they work because I have reduced spring pressure just enough to prevent coil bind. Then engine will rev to 6k NO PROBLEM.
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Quote:
Originally Posted by madmax
I think the argument is that swirl port heads suck in general.
..all stock heads suck, in general.
Last edited by 11sORbust; 11-25-2007 at 08:20 PM.
Reason: Automerged Doublepost
Re: TPI 305 with swirl port TBI heads *Myth BUSTED!
cool well you definately cleared that up i wasnt trying to be a **** i was just curious as to how you pulled it off. good job on the car. you should find a cammed LB9 and race him thatd be a great comparison.
Re: TPI 305 with swirl port TBI heads *Myth BUSTED!
My 310 TPI runs strong, despite having 187 casting swirl port heads on it. Pulls hard all the way up to 5,000+ RPM with the Production LT4 cam and 1.6:1 rockers that it has.
Re: TPI 305 with swirl port TBI heads *Myth BUSTED!
Quote:
Originally Posted by Fast355
My 310 TPI runs strong, despite having 187 casting swirl port heads on it. Pulls hard all the way up to 5,000+ RPM with the Production LT4 cam and 1.6:1 rockers that it has.
Re: TPI 305 with swirl port TBI heads *Myth BUSTED!
Quote:
Originally Posted by 11sORbust
Van, huh? COOL!
Yep, all 5,300 lbs of it with its 3.08 gears. I think the swirl port headed 305 does a GOOD job moving around the weight, despite the lack of proper mechanical advantage of lower gears.
For the poster doubting the 14.9, I have personally run a 15.1 from a stock automatic L03 car with nothing more than stickier tires, subframe connectors, and L.C.R.s. My brother and I got it down to a 14.35 @ 96 mph, on the STOCK longblock, prior to reducing the cars weight and opening up the long block. The 14.35 @ 96 mph run was made with the following mods.
L03 + L69 Dual snorkel air cleaner (Truck Lid & Filter), Long Tube Headers, 2 1/2" into single 3.5" exhaust, Late Model TBI PCM with Tuning, S10 stalled 4L60E trans, 3.42 gears, Drag Radial Tires, Lower Control Arm Relocation, Subframe connectors. Car handled and ran like a dream.
Re: TPI 305 with swirl port TBI heads *Myth BUSTED!
Quote:
Originally Posted by Fast355
For the poster doubting the 14.9, I have personally run a 15.1 from a stock automatic L03 car with nothing more than stickier tires, subframe connectors, and L.C.R.s. My brother and I got it down to a 14.35 @ 96 mph, on the STOCK longblock, prior to reducing the cars weight and opening up the long block. The 14.35 @ 96 mph run was made with the following mods.
L03 + L69 Dual snorkel air cleaner (Truck Lid & Filter), Long Tube Headers, 2 1/2" into single 3.5" exhaust, Late Model TBI PCM with Tuning, S10 stalled 4L60E trans, 3.42 gears, Drag Radial Tires, Lower Control Arm Relocation, Subframe connectors. Car handled and ran like a dream.
I still think you're a magician. The 14.35 I can believe, but 15.1 from tires, SFCs, and LCRs (I'm guessing that means LCA relocation brackets?) is VERY difficult to believe. 90% of the TBI board that has cams, headers, exhaust, etc are running half a second slower than you are with your stock ride. There's something more than those three mods you're not telling us.
Re: TPI 305 with swirl port TBI heads *Myth BUSTED!
In the other thread, you mentioned 220 rwhp and (?) 280 rw ftlbs. At what engine rpm were these numbers reached? Your engine makes a good comparison to Dewey316's 305 (started with stock TBI heads; then swapped in ported 416s). I don't recall what cam he used though, and I don't know how optimally tuned his/your combos were.
I also agree with the comment on stock heads, for heads older than 1996+ Vortec-type heads.
Re: TPI 305 with swirl port TBI heads *Myth BUSTED!
Quote:
Originally Posted by Kevin91Z
I still think you're a magician. The 14.35 I can believe, but 15.1 from tires, SFCs, and LCRs (I'm guessing that means LCA relocation brackets?) is VERY difficult to believe. 90% of the TBI board that has cams, headers, exhaust, etc are running half a second slower than you are with your stock ride. There's something more than those three mods you're not telling us.
Nope, that is basically it. The only other change was minor in the performance department, but were very benificial after more mods. The 700r4 had pucked and I put a 60E into it using the TBI truck PCM. The gear ratios in the 4L60E are identical to the 700r4, and I was running a very stock GM 305 Van tune.
Re: TPI 305 with swirl port TBI heads *Myth BUSTED!
Quote:
Originally Posted by Kevin91Z
I still think you're a magician. The 14.35 I can believe, but 15.1 from tires, SFCs, and LCRs (I'm guessing that means LCA relocation brackets?) is VERY difficult to believe. 90% of the TBI board that has cams, headers, exhaust, etc are running half a second slower than you are with your stock ride. There's something more than those three mods you're not telling us.
...then explain a heavy TBI vert running 15.3-15.0, only had aftermarket intake and exhaust.
Re: TPI 305 with swirl port TBI heads *Myth BUSTED!
Quote:
Originally Posted by kdrolt
I also agree with the comment on stock heads, for heads older than 1996+ Vortec-type heads.
..that is why I used the qualifier "generally". Vortecs RULE!
Quote:
In the other thread, you mentioned 220 rwhp and (?) 280 rw ftlbs. At what engine rpm were these numbers reached? Your engine makes a good comparison to Dewey316's 305 (started with stock TBI heads; then swapped in ported 416s). I don't recall what cam he used though, and I don't know how optimally tuned his/your combos were.
My tune is not perfect. Cannot recall where the peaks was at, rpm wise. I do know the dyno correction factor was set to SAE. Many magazines and "tuners" will use STD. The standard numbers with less graph smoothing would be about 232hp/297tq. I can post the dyno sheet if you like...
Re: TPI 305 with swirl port TBI heads *Myth BUSTED!
Quote:
Originally Posted by 11sORbust
...then explain a heavy TBI vert running 15.3-15.0, only had aftermarket intake and exhaust.
I want to clarify this perfectly . I was the owner of that car . I ran 14.9 on street tires . The mods at the time were : Edelbrock shorty headers and cat-back . Edelbrock Pro Flow air cleaner , and a 3:27 9 bolt posi . Also had injector spacer . With 150 shot of nitrous I ran a 13.2 @ 105 . Still on street tires . Went to the track with drag radials and blew out the clutch . Never made it back . My brother now owns the car and it has a 406 MPFI . He has never taken it to the track .
Last edited by 91RedRagtop; 06-22-2008 at 03:14 PM.
Reason: adding
