First dyno pull on the blown LT1 MGB

[Jim Stabe]

I have been chasing low rpm fuel trim imbalance between the two banks of cylinders but finally got the fuel trim problem solved - the brand new Bosch O2 sensors were reading off and the problem was resolved with the installation of two AC Delco sensors. The dyno guy got all the driveability and cold start tuning done and was making the first power pull. At 3800 rpm the blower was already at 7 lbs boost and made over 300 hp at the rear wheels. He estimates if he had kept going it would have been in the area of 450-475 hp and 12+ lbs boost - not a healthy situation with cast pistons and 11:1 compression. I'm picking the car up at lunch today and I'm interested in seeing what it feels like when it get on it at ~2500 rpm and then get out of it around 3500 rpm on the freeway. I'm shooting for 6-7 lbs of boost at 6000 rpm and 400-425 RWHP so a larger pulley is definitely a must. I'm trying to keep it conservative to extend the life of the engine, clutch and rear end.

 

[rmsg0040]

nice!

 

[holdover]

nice ride. sure do have enough HP/weight.

my toy ride is a '84 RX7 with a built 302/5 speed with C4 front and rear end and ZO6 wheels. The 302 is making a bit over 325HP, Crane cam/ better heads , next step is twin turbos. until I put the C4 F & R with the big tires and brakes it was dangerous, couldn't stop or turn.

 

[GCncsuHD]

Very nice! Love the MG's, I used to have a Midget myself.


Curious why you went with a built, higher compression LT-1 and FI, vs a cam/head/tuned LS that would be in the same neighborhood of power for a lot less $?

Either way, that thing will be a handful, very cool!

 

[Zeke]

That's a ridiculous amount of HP for an MG. Have fun!

 

[upndown]

You've been on that one for quite awhile Jim, Nice to see the fab work all done and its heart beating.

 

[4AudiQ]

Sub'ed.

 

[jayoldschool]

Just take the blower off. Still more power than you need, and the LT1 will last forever.

 

[Jim Stabe]

Very nice! Love the MG's, I used to have a Midget myself.


Curious why you went with a built, higher compression LT-1 and FI, vs a cam/head/tuned LS that would be in the same neighborhood of power for a lot less $?

Either way, that thing will be a handful, very cool!

It started out to be a cam/heads/tuned engine but then my good friend offered me the blower kit for a price I couldn't refuse. Of course he offered it to me after the engine was built. The kit is designed for a late C4 Corvette LT1/LT4 that had 10.4/10.8 compression. With the bigger cam I have it should be OK as long as I keep the boost at 6-7 lbs. I gave a good friend who had the same blower on a '96 LT4 Corvette and he drove it 50,000 hard miles.

I was driving it home from the dyno shop on the freeway at about 70 mph, put it in 5th and gave it about 1/2 throttle - maybe a touch more. It went from 70 to 90 quicker than I have felt in a very, very long time. It got up to just over 4 lbs of boost and really set me back in the seat. RPM went from 2500 to about 3200 rpm. I asked the dyno guy, Greg, what the torque was when it made the 300 RWHP and he said it was right at 360 ft lbs - at 3800 rpm! He also said he made another run on the dyno to 4500 rpm but didn't fully load it up and it made 10 lbs of boost. I definitely need to get that supercharger dialed back a few notches.

Boost really is addictive, I can remember when I had the turbocharged Olds 215 in the car and I had to dial the boost down from 15 lbs to 11-12 lbs, it seemed like the car suddenly weighed 1000 lbs more. Can't wait to get free rein to get on it through the gears to 6000 rpm.

 

[Jim Stabe]

Just take the blower off. Still more power than you need, and the LT1 will last forever.

Where's the fun in that??

 

[JonnyMac]

Changing supercharger pulley sizes is a very easy and effective way of altering boost characteristics..
Nice project too...

 

[Playwme]

I'm trying to keep it conservative to extend the life of the engine, clutch and rear end.

And rear tyres?

On second thought, they're going to be screwed no matter what. Very cool project.

 

[retfr8flyr]

One piece of advice, when you get into boost the RPM's will climb so fast it's almost impossible to get out of it by 3500 rpm. Since it hasn't even been tuned at the higher RPM's you are really risking blowing something from detonation and a stock bottom end. I know it's not what you want to hear but I would really recommend not getting into boost at all, until you get the larger pulley on it and get it tuned for that boost level.

Really neat project by the way. I am sure you will have lots of fun with it.

 

[bmxdad]

What are you tuning with?

Boost is addictive for sure

 

[ADSR]

looks like a blast!

 

[Jim Stabe]

One piece of advice, when you get into boost the RPM's will climb so fast it's almost impossible to get out of it by 3500 rpm. Since it hasn't even been tuned at the higher RPM's you are really risking blowing something from detonation and a stock bottom end. I know it's not what you want to hear but I would really recommend not getting into boost at all, until you get the larger pulley on it and get it tuned for that boost level.

Really neat project by the way. I am sure you will have lots of fun with it.

I hear you. I only did it once and only about 1/2 throttle in 5th gear so it didn't climb so fast I couldn't deal with it. I just had to feel the boost after waiting all this time.

What are you tuning with?

Boost is addictive for sure

I'm not doing the tuning, I'm having a dyno shop do it. I think they are using TunerCat but I'm not sure.

 

[JT-3]

That's a ridiculous amount of HP for an MG. Have fun!

Agreed. Too much juice, reminds me of my Honda s2000.

 

[CoopVA]

More pictures needed...


Sent from my iPad using Tapatalk

 

[skyking]

My sebring is pushing 415 hp and that is too much power........it is naturally aspirated and I can burn the tires off at nearly any speed.
The fun in cars like this is going quick , not fast .

 

[darwyn]

I'm trying to keep it conservative

I absolutely love this build, but that was some funny stuff right there!

 

[charleyw]

Nice! I remember seeing this car in one of the older "Engine Swap" books years ago. Pre-width mods of course. IIRC it had an aluminum 215 v8. I think I still have the book somewhere.
You have skills!

 

[Jim Stabe]

More pictures needed...


Sent from my iPad using Tapatalk

Open the links in my signature. There is now a part 4 that has a link at the top of all the 1st 3 parts

Nice! I remember seeing this car in one of the older "Engine Swap" books years ago. Pre-width mods of course. IIRC it had an aluminum 215 v8. I think I still have the book somewhere.
You have skills!

I just showed that article to a friend last week - hair was much darker then (1975). The pictures show a naturally aspirated Buick 215 that soon got replaced with a turbocharged Olds 215. There is a picture of the Olds in the part 1 link in my sig.

 

[38Chevy454]

Neat project and a lot of fun.

I had a much lower boosted vehicle, a 92 Chevy dually with a Whipple blown 454. even that was addicting!

 

[edsauto]

Do you not have a blow-off valve. I am helping a friend with a paxton and we are working our way up to 10 psi boost as soon as possible.

I would think you want to keep the pulley size and add a adjustable blow off.

Dan......

 

[PCO6]

I just showed that article to a friend last week - hair was much darker then (1975). The pictures show a naturally aspirated Buick 215 that soon got replaced with a turbocharged Olds 215. There is a picture of the Olds in the part 1 link in my sig.

The Buick 215 was a popular swap. As I'm sure you well know that engine was the foundation for the Rover V8 and was also used in the MGB/GT V8 and other British cars. It was a good engine.

Great job on your MGB.

 

[Jim Stabe]

Do you not have a blow-off valve. I am helping a friend with a paxton and we are working our way up to 10 psi boost as soon as possible.

I would think you want to keep the pulley size and add a adjustable blow off.

Dan......

Problem with a blowoff valve on a fuel injected engine is that it blows off air that has already been metered by the MAF and that will screw up the mixture calculations in the computer.

 

[colin39]

Jim ive always said the mg roadster needed something more, just always thought more hp, however 11 inches in width makes it a hole better looking car. Ive loved reading all 3 installments

 

[Jim Stabe]

Jim ive always said the mg roadster needed something more, just always thought more hp, however 11 inches in width makes it a hole better looking car. Ive loved reading all 3 installments

There is a 4th installment. Look at the top of any of the three and you will see links to all the others.

 

[retfr8flyr]

Problem with a blowoff valve on a fuel injected engine is that it blows off air that has already been metered by the MAF and that will screw up the mixture calculations in the computer.

You get around that by having a blow through instead of a draw through system and you put the blow off valve before the MAF sensor. The neat setup with a centrifugal is a waste gate, like on a turbo. The waste gate on a centrifugal blower allows a smaller pulley, for quicker boost buildup, and still keeps the boost at desired levels. You can run a pulley for 20 psi and have the waste gate set for like 12 psi. The blower will start making boost sooner but will not go over 12 lbs.

 

[skyking]

Some of you guys are smart as hell. I continue to be impressed with soooo many of you.


It seems that the "gas " guys have such better attitudes than the "diesel" crowd. They always end up in a pissin match because they all think they invented the wrench.I guess if I had to work on those stinkin nasty things ...I would be pissed also.

Just my observation !

 

[600SL]

Excellent thread. I love this. Cool but be carful.

 

[CoopVA]

Open the links in my signature. There is now a part 4 that has a link at the top of all the 1st 3 parts







I just showed that article to a friend last week - hair was much darker then (1975). The pictures show a naturally aspirated Buick 215 that soon got replaced with a turbocharged Olds 215. There is a picture of the Olds in the part 1 link in my sig.

Oh, I don't see the signatures on tap a talk app I'm using. I will check it out.

I've got a soft spot from MG-Bs... My dad taught me how to drive in one and made me take my drivers test in it. It was a blast!


Sent from my iPad using Tapatalk

 

[jwhcars]

Great build ! I have a friend that took a Karman Gia body and widened it. He then reskined a Porsche boxster with it. It is also one bad *** machine.

 

[Daedalus]

At 3800 rpm the blower was already at 7 lbs boost and made over 300 hp at the rear wheels. He estimates if he had kept going it would have been in the area of 450-475 hp and 12+ lbs boost - not a healthy situation with cast pistons and 11:1 compression. I'm picking the car up at lunch today and I'm interested in seeing what it feels like when it get on it at ~2500 rpm and then get out of it around 3500 rpm on the freeway. I'm shooting for 6-7 lbs of boost at 6000 rpm and 400-425 RWHP so a larger pulley is definitely a must. I'm trying to keep it conservative to extend the life of the engine, clutch and rear end.

A dyno can measure torque and RPMs; HP is a calculated value.

HP = [Torque]x[RPMs]/5252

300HP @ 3800 RPMs means that the car was already making 414 ft-lbs of torque during the run

400HP @ 6000 RPMs means you'll only be making 350 ft-lbs of torque. Not a small # by any means, and granted, this is at the rear wheels, but it sounds like you might risk a powertrain failure by boring the engine and supercharger to death.

Strongly recommend Corky Bell's Supercharged! book if you haven't already read it.

Looks like a very fun project, all in all. I have been looking for a Super Seven type of car for a couple of years now.

 

[Jim Stabe]

Got the larger pulley installed on the blower and dynoed it today, 450 rwhp at 4800 rpm and 543 rwtq at 4000 rpm. Boost at peak hp is about 6 lbs rising to 8 psi at 6000 rpm. If the 15% rule is true that is 517 fwhp and 625 fwtq. It makes over 400 rwtq from 2700 rpm to 5400 rpm. The car really accelerates!

 

[retfr8flyr]

Good numbers, that thing should be a rocket and really fun to drive.

 

[Jim Stabe]

Good numbers, that thing should be a rocket and really fun to drive.

I'll have to get more full throttle seat time before it gets to be really fun. Right now it's fun like a really scary roller coaster is fun

 

[American]

I'm shooting for 6-7 lbs of boost at 6000 rpm and 400-425 RWHP so a larger pulley is definitely a must. I'm trying to keep it conservative to extend the life of the engine, clutch and rear end.

I'm sorry but 'conservative' and 'blown LT1 MGB' shouldn't be uttered in the same post.

...and I love every bit of it!

 

[emeraldcoupe]

Got the larger pulley installed on the blower and dynoed it today, 450 rwhp at 4800 rpm and 543 rwtq at 4000 rpm. Boost at peak hp is about 6 lbs rising to 8 psi at 6000 rpm. If the 15% rule is true that is 517 fwhp and 625 fwtq. It makes over 400 rwtq from 2700 rpm to 5400 rpm. The car really accelerates!

awesome. gotta be a wicked sick ride!

 

[Wingnut65]

Awesome build, Jim. That is just an amazing amount of work you have done to bring this dream to life. Every engineering detail you have had to overcome is like engineering an brand new concept car. Wow!

And the tools that you build that you casually mention - the Ring Roller, the English Wheel! We'd love to see build details of the tools as well.

Beautiful car! Thanks for documenting the build process so well!