TBI Whipple Cam Selection

[Cadride]

When tuning TBI and EBL Flash are there any cam combinations that don’t work good together? I know some cams are specific to EFI, TBI and such and wanted to make sure that the new cam that I go with doesn’t conflict with the TBI and EBL systems; since I will probably have a custom cam made. My engine is a 355 with Whipple Supercharger and many modifications.

[EagleMark]

Split duration cam with exhaust being higher at max 224 @.050 duration and a high Lobe separation angle, ie.. less overlap. 113+

[1project2many]

SC cam should have reduced overlap anyway. Keeping both valves open with forced induction is a great way to blow fuel and air into a hot manifold and muffler. Bang!

[Cadride]

Thanks for the input. Mark I am trying to learn; can you explain to me, why you state: max 224 @.050 duration, lobe separation angle max 113 (I assume) and no split duration.

Current Cam and suggested by Comp Cams with old vortec heads
08-503-8, 224/230 @ .050, .509/.517 Lift, 112 LSA, 108 Intake Centerline

Cam Suggested by Lunati with new AFR 195 heads
Part# 20080721, 221/229 @.050 .515/.530 Lift, 112 LSA, 110 ICL
Or step up in cam
Custom Grind, 227/231 @ .050, 114 LSA, 110 ICL

All of these cams somewhat conflict with your recommendations or come close. By no means am I saying you are wrong, I think that most cam grinders don’t deal with TBI due to small market. I am hoping that I can learn and explain to them, why I may not be able to tune my engine very well with their cam.

[Cadride]

Little about my build: Redline 6000 rpm, EBL Flash computer, 355, Flat top pistons, 6" rods, 2.3 Whipple @ 10psi boost, AFR Eliminator 195 heads 76cc combustion, Static 9:1 CR, with current cam Dynamic 7:1 CR, Dynamic under boost 11.7:1 CR, Edelbrock Performer intake, Roller cam and rockers, 750 cfm 454 TBI bored to 54mm ports, Longtube headers 2 1/2 duals. In a 1994 C1500, 2wd, EXT, 4600lbs, 4l60E, 2500 stall, 3:73 gears. I also will need to be able to pass emissions.

On the dyno last year the engine only made 315 rwhp, but pulled 425 rwtq. This could be cause of many reasons: 9:54 CR, Vortec Heads, Cam didn't work with TBI computer, bad tune. Didn't have EBL installed and there were issues on dyno requiring to pull before engine was tuned.

[EagleMark]

The 113 lobe separation was minimum and duration were maximum. Reason I recommended this was idle and RPM power range ie no overlap issues at idle low RPM.

Both the cams you have and chose have an operating range from 1800 RPM up... at least you have a 2500 RPM stall convertor. so both I could tune to a TBI and it would drive good because of the converter, without it would suck off idle/dead zone...

Now you have to wait for 1project2many who is an actual engine builder to tell you how they will react to boost?

[EagleMark]

The 113 lobe separation was minimum and duration were maximum. Reason I recommended this was idle and RPM power range ie no overlap issues at idle low RPM.

Both the cams you have and chose have an operating range from 1800 RPM up... at least you have a 2500 RPM stall convertor. so both I could tune to a TBI and it would drive good because of the converter, without it would suck off idle/dead zone...

Now you have to wait for 1project2many who is an actual engine builder to tell you how they will react to boost?

[Cadride]

Nice to have tuner and engine builder on the thread

Thanks for the info Mark. The cam that is in it right now idled out pretty nice, but you are right about the dead spot. If you were planning for the hesitation off the line it wasn't horrible, but if you stomped it from a light you wouldn't go anywhere; that was also with a stock converter. The tuner that I was working with got the hesitation down, but never got rid of it. Sounds like, probably wouldn't be able to.

1project2many what cam would you suggest not being stuck to one that I posted or do you have a cam grinder that you would recommend?


I had one person recommend that with a TBI you shouldn't run over 210 duration; saying that is one of the reasons that my power dropped off quickly after 5000. I don't know what his expertise are to say he is right or wrong.

[1project2many]

Now you have to wait for 1project2many who is an actual engine builder to tell you how they will react to boost?

Waitaminute... Don't go getting me into trouble. I can give free advice on the internet but I'm no pro builder.

The stock TBI intake and the expensive Edelbrock version for Vortec heads are both very similar. Small bores, small ports, a very small plenum, and plenty of heat. Cam recommendations for the TBI usually work with this because the intake has a way of starving the ports at higher rpm. Trying to increase overlap only causes a bunch of reversion into the already small plenum which makes the mixture hard to burn at low rpm and gains very little on top.

I'm not sure which Performer intake you've got. Switching to a single plane carb intake for the Vortec heads and using a carb to TBI adapter on top helps top end flow considerably. It can get challenging when you start trying to make the low end driveable and consistent especially if you're using a computer that doesn't have any intake air temp measuring or compensation but this combination usually yields more power in the mid and upper rpm ranges. Using a cam with a *small* amount of overlap can help with low speed driveability by warming fuel/air right at the ports warm and can even help emissions slightly due to some EGR action but the difference between "just right" and "too much" is small.

The supercharger boost is tied to engine speed so the question is, where are you making boost? Can the SC cover a wide rpm range? For a relatively stock truck you're better off trying to produce peak power at low to mid rpm. Raising the power peak usually means a bunch of other changes... gear ratio, looser converter, fat exhaust, etcetera. 4600# truck on 3.73 gears isn't going to be a lightning bolt without a *bunch* of power to back it up. How far are you going in your search for more power? Or better yet, what are you looking for from the truck?

[Cadride]

Thanks much for the info and it makes a lot of sense, granted the TBI is probably one of the worst engines to start from as far as the performance it started with. I would love to do single plane but with having to pass emissions I am stuck with a EGR manifold. (I am planning on moving to CO and have not had to deal with emissions yet). Last year I had vortec heads with a GM vortec to 4 barrel intake. I made an adapter plate to mount the SC and made sure everything was opened up as much as possible. The air is pulled from the windshield cowl plenum not engine bay. The exhaust setup is Hooker longtube headers, 2 1/2" true duals with high flow cats, and X muffler, the converter is a Vigilante 2500 stall. The Supercharger is a Whipple and makes boost almost immediately, last years setup it did drop about 2 psi over the full rpm range though.

Here is a pic of my setup with the Vortec heads.
IMG_7310_zps5d0d5b14.jpg
2012-07-30134412_zpsd0c20204.jpg


Now I am changing to AFR 195 heads and a Edelbrock Performer 3701 intake. I am in the process of having the bottom end made now with .5 lower CR and beefed up the bottom end to take the power. I don't plan on racing this truck other than some friendly battles, like you said this is a tank. The end goal is a truck with street drivability, and reliability (as long as hard parts don't break) with as much power as I can make for the fun factor. This is a build that has gone way farther than ever planned and become quite addictive. I am up for suggestions on additional things to look at on my setup, with out spending a lot more or just starting over. With the way the power dropped off on the dyno and looking at Comp Cams dyno sheet off their website I think I can do better cam wise.

[Cadride]

Is this the correct formula for figuring cam overlap (INT Duration @ .050 + EXT Duration @ .050)/2-LSA*2 ?

[1project2many]

The formulas for overlap really fall apart when you start looking at lifter acceleration rates, split profile cams, and asymmetric cam lobes. They might give you a general idea but they're not good for getting the true details. A cam with less acceleration and a gentle transition around the base circle is going to hold the valve open longer below .050" lift than an aggressive cam even though the .050" duration is the same. You're better off using advertised duration, especially if they tell you what lift (.002", .004", etc) it's measured at.

Once upon a time you could download free software from Comp Cams that might help here. It's a version of Desktop Dyno locked to their camshafts and it's tied into software that recommends cams. It's ok although the HP estimates are as optimistic as the real desktop dyno. But what it could do is help you visualize how the shape of the lobe affects overlap. It could also allow you to play with Comp's cams to get some idea of which ones fit what you want from the engine.

I've got a pile of work to do right now. I'll get to the other stuff later.

[Cadride]

The stock TBI intake and the expensive Edelbrock version for Vortec heads are both very similar. Small bores, small ports, a very small plenum, and plenty of heat. Cam recommendations for the TBI usually work with this because the intake has a way of starving the ports at higher rpm. Trying to increase overlap only causes a bunch of reversion into the already small plenum which makes the mixture hard to burn at low rpm and gains very little on top.

I'm not sure which Performer intake you've got. Switching to a single plane carb intake for the Vortec heads and using a carb to TBI adapter on top helps top end flow considerably. It can get challenging when you start trying to make the low end driveable and consistent especially if you're using a computer that doesn't have any intake air temp measuring or compensation but this combination usually yields more power in the mid and upper rpm ranges. Using a cam with a *small* amount of overlap can help with low speed driveability by warming fuel/air right at the ports warm and can even help emissions slightly due to some EGR action but the difference between "just right" and "too much" is small.

The supercharger boost is tied to engine speed so the question is, where are you making boost? Can the SC cover a wide rpm range? For a relatively stock truck you're better off trying to produce peak power at low to mid rpm. Raising the power peak usually means a bunch of other changes... gear ratio, looser converter, fat exhaust, etcetera. 4600# truck on 3.73 gears isn't going to be a lightning bolt without a *bunch* of power to back it up. How far are you going in your search for more power? Or better yet, what are you looking for from the truck?

Couple of updates:
I now plan on putting an IAT sensor after the SC that will be tied in to the EBL.

At the local swap meet today I picked up a Weiald G Team single plane intake with EGR. Got the intake bolted on with SC today and I will have to make some changes to my mounts but the overall height from my GM Vortec intake and the G Team intake are almost identical. Do you think that I am making a mistake by putting on a single plane intake in my setup; I was pretty hesitate to buy it?? I am hoping that the SC will offset any bottom end loss in power, with my last set up I hit over 350 RWTQ at 3000 rpm and 425 RWTQ at 3400 rpm.

[Fast355]

You will not lose anything with a Single Plane, ONLY GAIN!

[Cadride]

Slowly getting me engine together should get short block back from machine shop next week, I did get feedback from Comp Cams, and Crane Cams; which both of them said to stick with my current cam, as I wouldn't see much of a performance gain from changing out cams. Comp did say they could make some upgrades if I didn't have emissions. This cam was suggested to me by a Cam designer which sounds like it could be an upgrade I am just worried about the dynamic CR since I make full boost around 3500 rpm.

· Duration @ .050 (Int/Exh): 216/228
· Lobe Lift (Int/Exh): .340"/.340"
· Gross Valve Lift w/1.6 (Int/Exh): .544/.544
· LSA 114
· Intake closing @.006" is 62 ABC
· Intake closing @.050" is 38 ABC
· Static CR 9:1, Dynamic CR 8.24, Dynamic w/boost CR 13.85:1
· Cranking Pressure 165 psi

What are your thoughts?