What spark plug for hot cam or other similiar engine mods

[LT4BUD]

So you do cam, head job, headers, maybe some other mods....
thinner head gaskets..

Does the stock spark plug, or oem specified equal, still work fine? Or do you go one or two stages colder????

This question is a little bit which brand, but mostly directed toward what heat range.....or style works best...

BTW I went with Denso Iridium IT20 which is one stage colder than Denso's specified IT16 for stock. I have unconfirmed reasons to believe either I should have gone to colder range or some other style..

Help....plugs are too hard to change to go experimenting...Denso's are also big $$$

 

[Shriker]

Mine are NGK's I beleive , I think they are TR55's but cant remember now...yikes. They have worked well with my combo......

 

[wx briefer]

NGK 55's here also. No problems.

 

[Ken]

plugs are too hard to change

Man, I am sooo-o glad that I don't have that problem anymore - I can change plugs in fifteen minutes. :cool

By the way, I'm running Champions a few ranges colder than stock (I'm using 9's instead of 12's), and a closer gap because of my Electronics; Rick recommended that I go to .028 instead of the normal .035 gap. I know, I know, Smokey went the other way, but he was building total race engines that would be working hard all the time. It gets hot, and stays hot in there. Mine's still streetable.

 

[LT4BUD]

BTW I went with Denso Iridium IT20 which is one stage colder than Denso's specified IT16 for stock

I am now running Denso IT24...........time will tell, so far ok.....

BTW this is another two stages colder over the IT20's plus a smaller gap from Denso

 

[Tuna]

I'm using the factory AC Delco plugs in my Hot Cammed and LT4tified 92. They have 8000 miles on them now and are okay. Time will tell.

 

[Hib Halverson]

For an engine modified as listed above, the Denso IT20 is the way to go for an LT4 in high-performance street use. I use Densos in all my Corvettes and have been very satisfied with the performance. I would not use anything colder unless the duty cycle is frequent racing and no starts with out warm-ups. In that case use the IT22.

The IT24, three ranges colder than stock and a non-projected tip, is only for race-only applcations

 

[LT4BUD]

This is what Denso told me.....I had some additional communication, but here is my last inquiry & their response...

Hi Bud,
I think the IT24 would be the better choice over the IT27. The reason why they changed the factory pre-set is because the colder heat ranges are used in performance applications where the spark is harder to jump the gap.
Thanks,
Aaron


07/29/2004 05:18 PM


To: AARON_BROCK@denso-diam.com
cc:
Subject: Re: Iridium Spark Plug



I am thinking I was going to go to either IT24 or
IT27. Before I do I would like your input.

The car is mostly street driven, but usually they are
"long" trips at interstate speed. A few shorter trips
up to the local cruise-ins and infreqruent trip to the
drag strip..

It seems though that the IT24 & IT27 are quite
different since they are factory set at .032 vs .044
for the It 16, IT20, & IT22.

Since I appear to have problems with IT20 I was
thinking to go at least 2 stages colder..

Looking for your input ASAP

Thanks

Bud Bennett

 

[Hib Halverson]

I talk to Aaron Brock frequently. He's my contact at Denso when I need information. While Aaron is a product expert on plugs in general, he's not always up on the latest Corvette details.

For this kind of duty...

The car is mostly street driven, but usually they are
"long" trips at interstate speed. A few shorter trips
up to the local cruise-ins and infreqruent trip to the
drag strip..

I'd recommend the IT20, one range colder than stock. Anything colder than that risks fouling when you do short trips or any useage where there is starts without warm-up. If you want, you could experiment with the IT22, but again, you risk fouling during sucessive starts without warm-up.

One thing that Aaron forgot to mention is the IT24 and colder are non-projected tip plugs.

 

[LT4BUD]

Thanks for the response....

I did run the IT20's for a while and I suspected they may have been giving me some detonation and spark retard......don't really know for sure.....I am going to try some data logging with my Autotap to see how I am doing now with the IT24's..

Another rule of thumb Aaron gave me was one stage colder for every 50hp over stock...I dyno 370rwhp, so motor wise I am probably just a tad over 100hp increase from stock.....which suggests 2-3 stages colder over stock..

Usually when I start the car it gets driven for some distance......rarely would it not get well warmed and more....usually highway speed..

The car actually has CompCams 503 cam and thinner gasket raising compression maybe 0.2 to about 11.0-11.1....plus peak hp is 6450rpm....right now I limit my revs to 6700....probably will stay with this, but power-wise the motor wants to run higher revs....except still stock bottom

Not sure what to do.......go back to IT20 as you have suggested, try IT22, stay with the IT24's for a little longer

Thanks for your input....any additional comments will be appreciated..