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L98 TPI 350 endurance race combination

General engine tech -- Drag Racing to Circle Track

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CastIron
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L98 TPI 350 endurance race combination

Post by CastIron »

In kicking around various choices to power a 3000 pound endurance road race car, I came across some dyno tests that intrigued me as they seemed to kinda blow up some commonly held ideas on the old low RPM TPI setup. Like this 410hp 383 with a stock TPI system on it. https://youtu.be/4ofiHKfhYkc?t=555

While with smaller, "street" cams the TPI generally does it's signature nose dive before 5000 rpm, it appears that with a much larger aggressive cam like a CC 294 the intake simply acts more like a restrictor. The HP stays damn near flat all the way to 6k, with a much higher torque and HP peak than the smaller cams. Much like a head/intake/carb restricted circle track motor.

I am limited on what I can do per the rules. The rules are rather odd compared to most racing series and frankly are import oriented, so without going into depth I will just say what I can and can't do;

Note-When I say endurance this thing as to be at 9/10's or more for up to 15 hours at tracks like Road America and Daytona. Long pulls.

For my particular car I am limited on how much "stock" power I can swap into it. To give an idea, I could swap a 4.8 255hp LS in but would have no points left to do any suspension work so that is out. Basically anything from 200 to 230hp stock will work and leave me with enough room to do mods to both the engine and the car/suspension. So, I'm thinking the 210HP L98 350 out of a 1987 GTA is the ideal starting point.

Note-I could go with a 240HP L98 out of the Vette to get the AL heads, but they would require a lot of port work. And the 30 extra horsepower over the GTA mill basically adds 100 points to the swap. Aftermarket AL heads cost 100 points, so....

My thinking is since the TPI is very restricted on it's own, the TFS 195 street CNC heads on the 410hp 383 in the video are a bit of overkill. My thought is some Profilers or Brodix IK in a 180cc should be sufficient with little to no porting as they flow around 245cfm iirc. Sound about right for a 350?

The chambers will be slightly larger at 64cc versus 58 so a deck or thin head gasket may be in order to get compression back. Can run on 92 octane.

The cam is a question mark. I've seen off the shelf 288's to 294's all exhibiting the same traits and similar power figures however I am curious if something more custom would not only make more power but possibly have better mileage. As this is endurance racing fuel mileage is something one should look at. In researching this I came across a post from UDHarold from years ago where he claimed to have a cam used in various road racing series at Daytona and Sebring that put out great power and got 8.7mpg. That seems a bit too good to be true, and I doubt that stick would be ideal for a TPI, but just wanted to bring it up due to the need for some mileage. Also, I have zero concern about street manners. It's a race car that will live between 3000 and 6000rpm. Generally shift at 5500 but the extra 500 is nice to avoid a shift here and there.

I'm looking for around 360-380HP at the crank out of the TPI 350. I put the power curve numbers into a lap simulator and with 453 torque/372HP the lap times looked very good. (That is 90% of the power of the above 383.) Even with 2.73's. Essentially the same lap times as with 3.08's.

Not looking for max power here and frankly that is why I'm liking the TPI idea. The lower rpm will be much easier on the valvetrain. If it comes up a bit short at 350fwp it would likely be fine as well as this is endurance racing, not sprint.

And to spell things out a bit clearer, the TPI has to stay as changing to a different intake/carb/throttle body costs points I don't want to spend. And no, I will not turbo/supercharge it. Yes, I know the same engine with a victor jr and carb would make 100 more horsepower. Don't care. Don't need 100 more HP and want some semblance of mileage for fuel stops.

I have some Shoenfeld 180 headers that I would love to use. Hopefully they are not off base for this as they give me plenty of room and ground clearance and most people will wonder how a TPI 350 is spinning 8 grand. (95% of competitors are imports that know next to nothing about a SBC)

The shortblock has to stay essentially stock as they have started snooping piston tops for some reason. Nothing says you can't change pistons but there is no point value so you are at the mercy of tech. "Everything has to be claimed" that you changed from stock.

Basically looking for cam ideas and some detail type work that will add power to this combo.

Ok, that was longer than expected but hopefully it describes what I am looking for fairly well. If not just let me know and I can expand. I didn't explain much about the points for parts as it was too long already. Also, feel free to say if this sounds completely off base, while suggesting something else. Just remember stock HP has to be 200 to possibly 230. Or less. Note-A 305 wouldn't require a swap saving 50 points but I'm thinking that to make the desired power it might be a bit too rowdy and hard on parts.

Thanks
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Re: L98 TPI 350 endurance race combination

Post by CastIron »

Forgot to add that it will be run with Holley HP, not the stock ecu.

Injectors are free points so if they need to be replaced with larger ones that is not a problem.
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Re: L98 TPI 350 endurance race combination

Post by BILL-C »

CHAMP car?
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Re: L98 TPI 350 endurance race combination

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BILL-C wrote: Sun May 02, 2021 9:11 amCHAMP car?
Yep. Engine will go in an 80's Monte or a 70's F body. Have also considered a C3 but they are not great for tall drivers with a coupe body.

There are a couple C4's running in Champcar that I assume are L98's that are fairly quick. They don't have any points to play with for engine mods however.

btw-In the first post the heads on the 383 were AFR 195 cnc street heads. Don't know where TFS came from.
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Re: L98 TPI 350 endurance race combination

Post by j-c-c »

Is a 4/7 swap penalized or detectable?
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Re: L98 TPI 350 endurance race combination

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j-c-c wrote: Sun May 02, 2021 11:12 pm Is a 4/7 swap penalized or detectable?
4/7 swap is fine.

Does it help with the tpi's somewhat restrictive plenum?
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Re: L98 TPI 350 endurance race combination

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CastIron wrote: Sun May 02, 2021 10:43 am
BILL-C wrote: Sun May 02, 2021 9:11 amCHAMP car?
Yep. Engine will go in an 80's Monte or a 70's F body. Have also considered a C3 but they are not great for tall drivers with a coupe body.

There are a couple C4's running in Champcar that I assume are L98's that are fairly quick. They don't have any points to play with for engine mods however.

btw-In the first post the heads on the 383 were AFR 195 cnc street heads. Don't know where TFS came from.
I would spend my points on the best road race oil pan i could buy, an accusump, and the best brake parts that are allowed before i invested points into making more power.
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Re: L98 TPI 350 endurance race combination

Post by CastIron »

BILL-C wrote: Mon May 03, 2021 12:51 pm
CastIron wrote: Sun May 02, 2021 10:43 am
BILL-C wrote: Sun May 02, 2021 9:11 amCHAMP car?
Yep. Engine will go in an 80's Monte or a 70's F body. Have also considered a C3 but they are not great for tall drivers with a coupe body.

There are a couple C4's running in Champcar that I assume are L98's that are fairly quick. They don't have any points to play with for engine mods however.

btw-In the first post the heads on the 383 were AFR 195 cnc street heads. Don't know where TFS came from.
I would spend my points on the best road race oil pan i could buy, an accusump, and the best brake parts that are allowed before i invested points into making more power.
Brakes are free points. Pan and accusump is 35 total as I recall.

This engine build/swap is all about conserving points so they can be spent on the suspension. I'm starting with a 150 point car.

The TPI idea gives awesome off the corner torque with sufficient HP while hopefully returning some mileage by allowing 2 series gears.

To run a 3000 pound car against 1900-2100 pound cars with 200hp means I need more than a stock L98. Pretty simple math there. And the races are being run not far from a sprint race pace over 7-8 and 14 hours. There are plenty of fast and reliable car in the series now. It's not like it was five years ago and not like Lemons at all. Closer to AER and WRL.

There are cars running low 2:10's at Daytona (road course) and 2:40's at Road America running the bend which adds 7-9 seconds. For comparison in 1970 the Trans Am cars at Road America the pole was 2:31. A 210HP Monte isn't going to come close.
Last edited by CastIron on Mon May 03, 2021 1:58 pm, edited 1 time in total.
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Re: L98 TPI 350 endurance race combination

Post by nhrastocker »

From 1988 thru 1992, there was a 1LE Camaro option with the L98 that was built for endurance road racing. It was also part of the old IROC series too. The 1LE package even had a fuel tank with dual pickups for preventing any fuel starvation through cornering.

https://www.hemmings.com/stories/2014/0 ... camaro-1le
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Re: L98 TPI 350 endurance race combination

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nhrastocker wrote: Mon May 03, 2021 1:56 pm From 1988 thru 1992, there was a 1LE Camaro option with the L98 that was built for endurance road racing. It was also part of the old IROC series too. The 1LE package even had a fuel tank with dual pickups for preventing any fuel starvation through cornering.

https://www.hemmings.com/stories/2014/0 ... camaro-1le
A stock 3rd gen 1LE would get blown off the track today. Cool cars for their time.

Newer cars are coming into the series with more power. A 2007 Altima SER with 260 factory HP is one of the current fastest cars. Tunes are free, as is exhaust after the header/manifold, so I am sure it is putting out far beyond it's rated 260.
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Re: L98 TPI 350 endurance race combination

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CastIron wrote: Mon May 03, 2021 2:01 pm
nhrastocker wrote: Mon May 03, 2021 1:56 pm From 1988 thru 1992, there was a 1LE Camaro option with the L98 that was built for endurance road racing. It was also part of the old IROC series too. The 1LE package even had a fuel tank with dual pickups for preventing any fuel starvation through cornering.

https://www.hemmings.com/stories/2014/0 ... camaro-1le
A stock 3rd gen 1LE would get blown off the track today. Cool cars for their time.

Newer cars are coming into the series with more power. A 2007 Altima SER with 260 factory HP is one of the current fastest cars. Tunes are free, as is exhaust after the header/manifold, so I am sure it is putting out far beyond it's rated 260.
My reference was about the car itself, equipped with suspension, etc... Of course the OEM engine could not keep up with the current available high performance cars.
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Re: L98 TPI 350 endurance race combination

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nhrastocker wrote: Mon May 03, 2021 4:20 pm
CastIron wrote: Mon May 03, 2021 2:01 pm
nhrastocker wrote: Mon May 03, 2021 1:56 pm From 1988 thru 1992, there was a 1LE Camaro option with the L98 that was built for endurance road racing. It was also part of the old IROC series too. The 1LE package even had a fuel tank with dual pickups for preventing any fuel starvation through cornering.

https://www.hemmings.com/stories/2014/0 ... camaro-1le
A stock 3rd gen 1LE would get blown off the track today. Cool cars for their time.

Newer cars are coming into the series with more power. A 2007 Altima SER with 260 factory HP is one of the current fastest cars. Tunes are free, as is exhaust after the header/manifold, so I am sure it is putting out far beyond it's rated 260.
My reference was about the car itself, equipped with suspension, etc... Of course the OEM engine could not keep up with the current available high performance cars.
There are some 3rd gen F bodies running but they are hampered by the small fuel tanks. They handle well with some minor changes but adding power just makes the fuel issue worse.

Fuel tanks are either stock or allowed +2 gallons if changed to a fuel cell, which puts the 3rd gen at 17.5 gallons iirc. The Altima I mentioned has 22 gallons.

Choosing a car is as much about the size of the fuel tank as anything else a lot of the time.
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Re: L98 TPI 350 endurance race combination

Post by BLSTIC »

I'd look at pulling all the fuel economy tricks you can. Including/especially running the latest model injectors you can find. Toyota was running Denso UC injectors Denso the 00's and their tapered 12-hole injectors were good for notable response, economy and emissions gains on the ev1/ev6 equipped jeep engines. I imagine their later larger 4 cylinder injectors would be perfect for a 350-400hp on a V8.

Maybe look into port texturing too
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Re: L98 TPI 350 endurance race combination

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BLSTIC wrote: Mon May 03, 2021 11:45 pm I'd look at pulling all the fuel economy tricks you can. Including/especially running the latest model injectors you can find. Toyota was running Denso UC injectors Denso the 00's and their tapered 12-hole injectors were good for notable response, economy and emissions gains on the ev1/ev6 equipped jeep engines. I imagine their later larger 4 cylinder injectors would be perfect for a 350-400hp on a V8.

Maybe look into port texturing too
Good stuff. I'll look into it.

Thanks.
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Re: L98 TPI 350 endurance race combination

Post by n2omike »

It's going to be HARD to run with modern Japanese sedans... especially with their all aluminum DOHC engines, advanced suspensions and light weight... and that's without even considering fuel mileage and 'family car' fuel tanks. I would think a Honda Accord, Acura equivalent or similar offerings from Nissan/Infinity would be the hot ticket. I had a Nissan Maxima at one time, and that thing was nice... I can imagine it with the stick shift!
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